@article{wells_aguilos_huang_gao_hou_huang_liao_lin_zhao_qiu_et al._2023, title={Attributing interannual variability of net ecosystem exchange to modeled ecological processes in forested wetlands of contrasting stand age}, volume={9}, ISSN={["1572-9761"]}, DOI={10.1007/s10980-023-01768}, journal={LANDSCAPE ECOLOGY}, author={Wells, Jon M. and Aguilos, Maricar and Huang, Xin and Gao, Yuan and Hou, Enqing and Huang, Wenjuan and Liao, Cuijuan and Lin, Lin and Zhao, Ruiying and Qiu, Han and et al.}, year={2023}, month={Sep} }
 @article{wells_aguilos_huang_gao_hou_huang_liao_lin_zhao_qiu_et al._2023, title={Attributing interannual variability of net ecosystem exchange to modeled ecological processes in forested wetlands of contrasting stand age}, volume={38}, ISSN={0921-2973 1572-9761}, url={http://dx.doi.org/10.1007/s10980-023-01768-x}, DOI={10.1007/s10980-023-01768-x}, number={12}, journal={Landscape Ecology}, publisher={Springer Science and Business Media LLC}, author={Wells, Jon M. and Aguilos, Maricar and Huang, Xin and Gao, Yuan and Hou, Enqing and Huang, Wenjuan and Liao, Cuijuan and Lin, Lin and Zhao, Ruiying and Qiu, Han and et al.}, year={2023}, month={Sep}, pages={3985–3998} }
 @article{fischer_katul_noormets_poznikova_domec_orsag_zalud_trnka_king_2023, title={Merging flux-variance with surface renewal methods in the roughness sublayer and the atmospheric surface layer}, volume={342}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2023.109692}, abstractNote={Two micrometeorological methods utilizing high-frequency sampled air temperature were tested against eddy covariance (EC) sensible heat flux (H) measurements at three sites representing agricultural, agro-forestry, and forestry systems. The two methods cover conventional and newly proposed forms of the flux-variance (FV) and surface renewal (SR) schemes of differing complexities. The sites represent measurements in surface, roughness, and roughness to surface transitional layers. Regression analyzes against EC show that the most reliable FV and SR forms estimate H with slopes within ±10% from unity and coefficient of determination R2>0.9 across all the three sites. The best performance of both FV and SR was found at the agricultural site with measurements well within the surface layer, while the worst was found for the tall forest with measurements within the roughness sublayer where its thickness needed to be additionally estimated. The main variable driving H in FV is the temperature variance, whereas in SR, it is the geometry of ramp-like structures. Since these structures are also responsible for most of the temperature variance, a novel FV-SR approach emerging from combining the methods is proposed and evaluated against EC measurements and conventional FV and SR schemes. The proposed FV-SR approach requiring only a single fast response thermocouple is potentially independent of calibration and ameliorates some of the theoretical objections that arise when combining ramp statistics with similarity arguments. The combination of methods also provides new insights into the contribution of coherent structures to the temperature variance and its dependence on atmospheric stratification. Other potential utility of the new method is to include it in multi-tool assessments of surface energy fluxes, since a convergence or divergence of the results has a high diagnostic value.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Fischer, Milan and Katul, Gabriel and Noormets, Asko and Poznikova, Gabriela and Domec, Jean-Christophe and Orsag, Matej and Zalud, Zdenek and Trnka, Miroslav and King, John S.}, year={2023}, month={Nov} }
 @article{mcnicol_fluet-chouinard_ouyang_knox_zhang_aalto_bansal_chang_chen_delwiche_et al._2023, title={Upscaling Wetland Methane Emissions From the FLUXNET-CH4 Eddy Covariance Network (UpCH4 v1.0): Model Development, Network Assessment, and Budget Comparison}, volume={4}, ISSN={["2576-604X"]}, DOI={10.1029/2023AV000956}, abstractNote={Abstract}, number={5}, journal={AGU ADVANCES}, author={McNicol, Gavin and Fluet-Chouinard, Etienne and Ouyang, Zutao and Knox, Sara and Zhang, Zhen and Aalto, Tuula and Bansal, Sheel and Chang, Kuang-Yu and Chen, Min and Delwiche, Kyle and et al.}, year={2023}, month={Oct} }
 @article{miao_noormets_gavazzi_mitra_domec_sun_mcnulty_king_2022, title={Beyond carbon flux partitioning: Carbon allocation and nonstructural carbon dynamics inferred from continuous fluxes}, ISSN={["1939-5582"]}, DOI={10.1002/eap.2655}, abstractNote={Abstract}, journal={ECOLOGICAL APPLICATIONS}, author={Miao, Guofang and Noormets, Asko and Gavazzi, Michael and Mitra, Bhaskar and Domec, Jean-Christophe and Sun, Ge and McNulty, Steve and King, John S.}, year={2022}, month={Jul} }
 @article{lin_noormets_king_marshall_akers_cucinella_fox_laviner_martin_mcnulty_et al._2022, title={Spatial variability in tree-ring carbon isotope discrimination in response to local drought across the entire loblolly pine natural range}, volume={42}, ISSN={["1758-4469"]}, DOI={10.1093/treephys/tpab097}, abstractNote={Abstract}, number={1}, journal={TREE PHYSIOLOGY}, author={Lin, Wen and Noormets, Asko and King, John S. and Marshall, John and Akers, Madison and Cucinella, Josh and Fox, Thomas R. and Laviner, Marshall A. and Martin, Timothy A. and Mcnulty, Steve and et al.}, year={2022}, month={Jan}, pages={44–58} }
 @article{lin_domec_ward_marshall_king_laviner_fox_west_sun_mcnulty_et al._2022, title={Using delta C-13 and delta O-18 to analyze loblolly pine (Pinus taeda L.) response to experimental drought and fertilization (vol 39, pg 1984, 2019)}, volume={42}, ISSN={["1758-4469"]}, DOI={10.1093/treephys/tpab162}, number={4}, journal={TREE PHYSIOLOGY}, author={Lin, Wen and Domec, Jean-Christophe and Ward, Eric J. and Marshall, John and King, John S. and Laviner, Marshall A. and Fox, Thomas R. and West, Jason B. and Sun, Ge and McNulty, Steve and et al.}, year={2022}, month={Apr}, pages={703–703} }
 @article{domec_king_carmichael_overby_wortemann_smith_miao_noormets_johnson_2021, title={Aquaporins, and not changes in root structure, provide new insights into physiological responses to drought, flooding, and salinity}, volume={72}, ISSN={["1460-2431"]}, DOI={10.1093/jxb/erab100}, abstractNote={Abstract}, number={12}, journal={JOURNAL OF EXPERIMENTAL BOTANY}, author={Domec, Jean-Christophe and King, John S. and Carmichael, Mary J. and Overby, Anna Treado and Wortemann, Remi and Smith, William K. and Miao, Guofang and Noormets, Asko and Johnson, Daniel M.}, year={2021}, month={May}, pages={4489–4501} }
 @article{aguilos_sun_noormets_domec_mcnulty_gavazzi_prajapati_minick_mitra_king_2021, title={Ecosystem Productivity and Evapotranspiration Are Tightly Coupled in Loblolly Pine (Pinus taeda L.) Plantations along the Coastal Plain of the Southeastern U.S.}, volume={12}, ISSN={1999-4907}, url={http://dx.doi.org/10.3390/f12081123}, DOI={10.3390/f12081123}, abstractNote={Forest water use efficiency (WUE), the ratio of gross primary productivity (GPP) to evapotranspiration (ET), is an important variable to understand the coupling between water and carbon cycles, and to assess resource use, ecosystem resilience, and commodity production. Here, we determined WUE for managed loblolly pine plantations over the course of a rotation on the coastal plain of North Carolina in the eastern U.S. We found that the forest annual GPP, ET, and WUE increased until age ten, which stabilized thereafter. WUE varied annually (2–44%), being higher at young plantation (YP, 3.12 ± 1.20 g C kg−1 H2O d−1) compared to a mature plantation (MP, 2.92 ± 0.45 g C kg−1 H2O d−1), with no distinct seasonal patterns. Stand age was strongly correlated with ET (R2 = 0.71) and GPP (R2 = 0.64). ET and GPP were tightly coupled (R2 = 0.86). Radiation and air temperature significantly affected GPP and ET (R2 = 0.71 − R2 = 0.82) at a monthly scale, but not WUE. Drought affected WUE (R2 = 0.35) more than ET (R2 = 0.25) or GPP (R2 = 0.07). A drought enhanced GPP in MP (19%) and YP (11%), but reduced ET 7% and 19% in MP and YP, respectively, resulting in a higher WUE (27–32%). Minor seasonal and interannual variation in forest WUE of MP (age > 10) suggested that forest functioning became stable as stands matured. We conclude that carbon and water cycles in loblolly pine plantations are tightly coupled, with different characteristics in different ages and hydrologic regimes. A stable WUE suggests that the pine ecosystem productivity can be readily predicted from ET and vice versa. The tradeoffs between water and carbon cycling should be recognized in forest management to achieve multiple ecosystem services (i.e., water supply and carbon sequestration).}, number={8}, journal={Forests}, publisher={MDPI AG}, author={Aguilos, Maricar and Sun, Ge and Noormets, Asko and Domec, Jean-Christophe and McNulty, Steven and Gavazzi, Michael and Prajapati, Prajaya and Minick, Kevan J. and Mitra, Bhaskar and King, John}, year={2021}, month={Aug}, pages={1123} }
 @article{aguilos_sun_noormets_domec_mcnulty_gavazzi_minick_mitra_prajapati_yang_et al._2021, title={Effects of land-use change and drought on decadal evapotranspiration and water balance of natural and managed forested wetlands along the southeastern US lower coastal plain}, volume={303}, ISSN={["1873-2240"]}, url={https://doi.org/10.1016/j.agrformet.2021.108381}, DOI={10.1016/j.agrformet.2021.108381}, abstractNote={Forested wetlands are important in regulating regional hydrology and climate. However, long-term studies on the hydrologic impacts of converting natural forested wetlands to pine plantations are rare for the southern US. From 2005-2018, we quantified water cycling in two post-harvest and newly-planted loblolly pine (Pinus taeda) plantations (YP2–7, 2–7 yrs old; YP2–8, 2–8 yrs old), a rotation-age loblolly pine plantation (MP, 15–28 yrs old), and a natural bottomland hardwood forest (BHF, > 100 yrs old) along the lower coastal plain of North Carolina. We quantified the differences in inter-annual and seasonal water balance and trends of evapotranspiration (ET) using eddy covariance over 37 site-years and assessed key climatic and biological drivers of ET. We found that the rotation-age plantation (MP) had higher annual ET (933 ± 63 mm) than the younger plantations (776 ± 74 mm for YP2–7 and 638 ± 190 mm for YP2–8), and the BHF (743 ± 172 mm), owing to differences in stand age, canopy cover, and micrometeorology. Chronosequence analysis of the pine sites showed that ET increased with stand age up to 10 years, then gradually stabilized for the remainder of the rotation of 28 – 30 years. YP2–8 was sensitive to water availability, decreasing ET by 30 – 43 % during the extreme 2007 – 2008 drought, but reductions in ET at MP were only 8 – 11 %. Comparing to BHF, ditching with management enhanced drainage at YP2–7 and YP2–8, while drainage was lower at the mature pine site. This study provides insight into land use-hydrology-climate interactions that have important implications for forested wetland management in a time of rapidly changing environmental conditions of the LCP of the southern US.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Aguilos, Maricar and Sun, Ge and Noormets, Asko and Domec, Jean-Christophe and McNulty, Steve and Gavazzi, Michael and Minick, Kevan and Mitra, Bhaskar and Prajapati, Prajaya and Yang, Yun and et al.}, year={2021}, month={Jun} }
 @article{noormets_bracho_ward_seiler_strahm_lin_mcelligott_domec_gonzalez-benecke_jokela_et al._2021, title={Heterotrophic Respiration and the Divergence of Productivity and Carbon Sequestration}, volume={48}, ISSN={["1944-8007"]}, DOI={10.1029/2020GL092366}, abstractNote={Abstract}, number={7}, journal={GEOPHYSICAL RESEARCH LETTERS}, author={Noormets, Asko and Bracho, Rosvel and Ward, Eric and Seiler, John and Strahm, Brian and Lin, Wen and McElligott, Kristin and Domec, Jean-Christophe and Gonzalez-Benecke, Carlos and Jokela, Eric J. and et al.}, year={2021}, month={Apr} }
 @article{aguilos_brown_minick_fischer_ile_hardesty_kerrigan_noormets_king_2021, title={Millennial-Scale Carbon Storage in Natural Pine Forests of the North Carolina Lower Coastal Plain: Effects of Artificial Drainage in a Time of Rapid Sea Level Rise}, volume={10}, ISSN={2073-445X}, url={http://dx.doi.org/10.3390/land10121294}, DOI={10.3390/land10121294}, abstractNote={Coastal forested wetlands provide important ecosystem services along the southeastern region of the United States, but are threatened by anthropogenic and natural disturbances. Here, we examined the species composition, mortality, aboveground biomass, and carbon content of vegetation and soils in natural pine forests of the lower coastal plain in eastern North Carolina, USA. We compared a forest clearly in decline (termed “ghost forest”) adjacent to a roadside canal that had been installed as drainage for a road next to an adjacent forest subject to “natural” hydrology, unaltered by human modification (termed “healthy forest”). We also assessed how soil organic carbon (SOC) accumulation changed over time using 14C radiocarbon dating of wood sampled at different depths within the peat profile. Our results showed that the ghost forest had a higher tree density at 687 trees ha−1, and was dominated by swamp bays (Persea palustric), compared to the healthy forest, which had 265 trees ha−1 dominated by pond pine (Pinus serotina Michx). Overstory tree mortality of the ghost forest was nearly ten times greater than the healthy forest (p < 0.05), which actually contributed to higher total aboveground biomass (55.9 ± 12.6 Mg C ha−1 vs. 27.9 ± 8.7 Mg ha−1 in healthy forest), as the dead standing tree biomass (snags) added to that of an encroaching woody shrub layer during ecosystem transition. Therefore, the total aboveground C content of the ghost forest, 33.98 ± 14.8 Mg C ha−1, was higher than the healthy forest, 24.7 ± 5.2 Mg C ha−1 (p < 0.05). The total SOC stock down to a 2.3 m depth in the ghost forest was 824.1 ± 46.2 Mg C ha−1, while that of the healthy forest was 749.0 ± 170.5 Mg C ha−1 (p > 0.05). Carbon dating of organic sediments indicated that, as the sample age approaches modern times (surface layer year 2015), the organic soil accumulation rate (1.11 to 1.13 mm year−1) is unable to keep pace with the estimated rate of recent sea level rise (2.1 to 2.4 mm year−1), suggesting a causative relationship with the ecosystem transition occurring at the site. Increasing hydrologic stress over recent decades appears to have been a major driver of ecosystem transition, that is, ghost forest formation and woody shrub encroachment, as indicated by the far higher overstory tree mortality adjacent to the drainage ditch, which allows the inland propagation of hydrologic/salinity forcing due to SLR and extreme storms. Our study documents C accumulation in a coastal wetland over the past two millennia, which is now threatened due to the recent increase in the rate of SLR exceeding the natural peat accumulation rate, causing an ecosystem transition with unknown consequences for the stored C; however, much of it will eventually be returned to the atmosphere. More studies are needed to determine the causes and consequences of coastal ecosystem transition to inform the modeling of future coastal wetland responses to environmental change and the estimation of regional terrestrial C stocks and flux.}, number={12}, journal={Land}, publisher={MDPI AG}, author={Aguilos, Maricar and Brown, Charlton and Minick, Kevan and Fischer, Milan and Ile, Omoyemeh J. and Hardesty, Deanna and Kerrigan, Maccoy and Noormets, Asko and King, John}, year={2021}, month={Nov}, pages={1294} }
 @article{minick_mitra_li_fischer_aguilos_prajapati_noormets_king_2021, title={Wetland microtopography alters response of potential net CO2 and CH4 production to temperature and moisture: Evidence from a laboratory experiment}, volume={402}, ISSN={["1872-6259"]}, url={https://doi.org/10.1016/j.geoderma.2021.115367}, DOI={10.1016/j.geoderma.2021.115367}, abstractNote={Coastal wetlands store significant amounts of carbon (C) belowground, which may be altered through effects of rising temperature and changing hydrology on CO2 and CH4 fluxes and related microbial activities. Wetland microtopography (hummock-hollow) also plays a critical role in mediating plant growth, microbial activity, and thus cycling of C and nutrients and may interact with rising seas to influence coastal wetland C dynamics. Recent evidence suggests that CH4 production in oxygenated surface soils of freshwater wetlands may contribute substantially to global CH4 production, but comprehensive studies linking potential CH4 production to environmental and microbial variables in temperate freshwater forested wetlands are lacking. This study investigated effects of temperature, moisture, and microtopography on potential net CO2 and CH4 production and extracellular enzyme activity (β-glucosidase, xylosidase, phenol oxidase, and peroxidase) in peat soils collected from a freshwater forested wetland in coastal North Carolina, USA. Soils were retrieved from three microsites (hummock, hollow, and subsurface peat soils (approximately 20–40 cm below surface)) and incubated at two temperatures (27 °C and 32 °C) and soil water contents (65% and 100% water holding capacity (WHC)). Hummocks had the highest cumulative potential net CO2 (13.7 ± 0.90 mg CO2-C g soil−1) and CH4 (1.8 ± 0.42 mg CH4-C g soil−1) production and enzyme activity, followed by hollows (8.7 ± 0.91 mg CO2-C g soil−1 and 0.5 ± 0.12 mg CH4-C g soil−1) and then subsurface soils (5.7 ± 0.70 mg CO2-C g soil−1 and 0.04 ± 0.019 mg CH4-C g soil−1). Fully saturated soils had lower potential net CO2 production (50–80%) and substantially higher potential net CH4 production compared to non-saturated soils (those incubated at 65% WHC). Soils incubated at 32 °C increased potential net CO2 (24–34%) and CH4 (56–404%) production under both soil moisture levels compared to those incubated at 27 °C. The Q10 values for potential net CO2 and CH4 production ranged from 1.5 to 2.3 and 3.3–8.8, respectively, and did not differ between any microsites or soil water content. Enrichment of δ13CO2-C was found in saturated soils from all microsites (−24.4 to − 29.7 ‰) compared to non-saturated soils (−31.1 to − 32.4 ‰), while δ13CH4-C ranged from −62 to −55‰ in saturated soils. Together, the CO2 and CH4 δ13C data suggest that acetoclastic methanogenesis is an important pathway for CH4 production in these wetlands. A positive relationship (Adj. R2 = 0.40) between peroxidase activity and CH4 production was also found, indicating that peroxidase activity may be important in providing fermented C substrates to acetoclastic methanogenic communities and contribute to anaerobic C mineralization. These results suggest that changes in temperature and hydrology could stimulate CO2 and CH4 emissions from surface hummock soils, and to a lesser extent from hollow soils, and provide preliminary evidence that hummocks may be a spatially important and unrecognized hotspot for CH4 production.}, journal={GEODERMA}, author={Minick, Kevan J. and Mitra, Bhaskar and Li, Xuefeng and Fischer, Milan and Aguilos, Maricar and Prajapati, Prajaya and Noormets, Asko and King, John S.}, year={2021}, month={Nov} }
 @article{li_minick_luff_noormets_miao_mitra_domec_sun_mcnulty_king_2020, title={Effects of Microtopography on Absorptive and Transport Fine Root Biomass, Necromass, Production, Mortality and Decomposition in a Coastal Freshwater Forested Wetland, Southeastern USA}, volume={23}, ISSN={["1435-0629"]}, DOI={10.1007/s10021-019-00470-x}, abstractNote={Forested wetlands are an important carbon (C) sink. Fine roots (diameter < 2 mm) dominate belowground C cycling and can be functionally defined into absorptive roots (order 1–2) and transport roots (order ≥ 3). However, effects of microtopography on the function-based fine root dynamics in forested wetlands are poorly understood. We studied fine root biomass allocation and biomass, necromass, mass loss rate, production, mortality and decomposition of absorptive and transport roots in hummocks and hollows in a coastal plain freshwater forested wetland (FFW) in the southeastern USA using dynamic-flow method. Biomass ratios of first- to second-order roots and absorptive to transport roots and the biomass and necromass of absorptive and transport roots were significantly higher in top 0–10 cm organic peat layer than in 10–20 cm muck and mineral layer, and were significantly higher in hummocks than in hollows. The mass loss rate, production, mortality and decomposition were significantly higher in hummocks than in hollows. Absorptive roots did not have a lower mass loss rate than transport roots. Microtopography significantly affected the contributions of absorptive and transport roots to the total production, mortality and decomposition. Production, mortality and decomposition of absorptive roots were higher than those of transport roots in hummocks but lower than those of transport roots in hollows. Total (hummocks plus hollows) fine root production, mortality and decomposition were 455 ± 106 g m−2 y−1, 475 ± 79 g m−2 y−1 and 392 ± 60 g m−2 y−1, respectively. Greater mortality than decomposition resulted in net fine root C input to soil. The observed microtopographic controls on fine root dynamics have great implications for soil C cycling. As sea level rises, the relative area of hollows in coastal plain FFWs will increase, causing a decrease in fine root mass loss rate, biomass, production, mortality and decomposition and it is the balance of these processes that will determine future soil C storage and cycling.}, number={6}, journal={ECOSYSTEMS}, author={Li, Xuefeng and Minick, Kevan J. and Luff, Jordan and Noormets, Asko and Miao, Guofang and Mitra, Bhaskar and Domec, Jean-Christophe and Sun, Ge and McNulty, Steven and King, John S.}, year={2020}, month={Sep}, pages={1294–1308} }
 @article{aguilos_mitra_noormets_minick_prajapati_gavazzi_sun_mcnulty_li_domec_et al._2020, title={Long-term carbon flux and balance in managed and natural coastal forested wetlands of the Southeastern USA}, volume={288}, ISSN={["1873-2240"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85085132484&partnerID=MN8TOARS}, DOI={10.1016/j.agrformet.2020.108022}, abstractNote={Wetlands store large carbon (C) stocks and play important roles in biogeochemical C cycling. However, the effects of environmental and anthropogenic pressures on C dynamics in lower coastal plain forested wetlands in the southern U.S. are not well understood. We established four eddy flux stations in two post-harvest and newly-planted loblolly pine plantations (YP2–6, 2–6 yrs old; YP2–8, 2–8 yrs old), a rotation-aged loblolly pine plantations (MP, 15–27 yrs old), and a mixed bottomland hardwood forest (BHF, >100 yrs old) in the lower coastal plain of North Carolina, USA. We analyzed the gross primary productivity (GPP), ecosystem respiration (RE) and net ecosystem exchange (NEE) for age-related trends, interannual variability in response to climate forcing, and management-related disturbances from 2005 – 2017. For the first few years after being harvested, pine plantations were net C sources (NEE = 1133 and 897 g C m–2 yr–1 in YP2–6 and YP2–8, respectively). The MP was a strong C sink (–369 to –1131 g C m–2 yr–1) over the entire study period. In contrast, BHF was a C source (NEE = 87 g C m–2 yr–1 to 759 g C m–2 yr–1) in most years, although in the first year it did show a net C uptake (NEE = –368 g C m–2 yr–1). The source activity of BHF may have been related to increasing overstory tree mortality and diameter growth suppression. Decreases in relative extractable water in pine plantations enhanced GPP and RE. Pine plantations regained status as C sinks 5–8 years after harvest and recovered C equivalent to post-harvest losses at 8–14 years. Thus, coastal pine plantations have a net C uptake for only about half the 25-year rotation period, suggesting that they have decreased climate mitigation potential in comparison to protecting primary forests. However, primary forests in this area may be vulnerable to ecosystem transition, and subsequent C loss, due to the changing environmental conditions at the land-ocean interface.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, publisher={Elsevier BV}, author={Aguilos, Maricar and Mitra, Bhaskar and Noormets, Asko and Minick, Kevan and Prajapati, Prajaya and Gavazzi, Michael and Sun, Ge and McNulty, Steve and Li, Xuefeng and Domec, Jean-Christophe and et al.}, year={2020}, month={Jul} }
 @article{hannun_wolfe_kawa_hanisco_newman_alfieri_barrick_clark_digangi_diskin_et al._2020, title={Spatial heterogeneity in CO2, CH4, and energy fluxes: insights from airborne eddy covariance measurements over the Mid-Atlantic region}, volume={15}, ISSN={["1748-9326"]}, DOI={10.1088/1748-9326/ab7391}, abstractNote={Abstract}, number={3}, journal={ENVIRONMENTAL RESEARCH LETTERS}, author={Hannun, Reem A. and Wolfe, Glenn M. and Kawa, S. Randy and Hanisco, Thomas F. and Newman, Paul A. and Alfieri, Joseph G. and Barrick, John and Clark, Kenneth L. and DiGangi, Joshua P. and Diskin, Glenn S. and et al.}, year={2020}, month={Mar} }
 @article{mitra_minick_miao_domec_prajapati_mcnulty_sun_king_noormets_2020, title={Spectral evidence for substrate availability rather than environmental control of methane emissions from a coastal forested wetland}, volume={291}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2020.108062}, abstractNote={Knowledge of the dynamics of methane (CH4) fluxes across coastal freshwater forested wetlands, such as those found in the southeastern US remains limited. In the current study, we look at the spectral properties of ecosystem net CH4 exchange (NEECH4) time series, and its cospectral behavior with key environmental conditions (temperature (Ts5), water table (WTD) and atmospheric pressure (Pa)) and physiological fluxes (photosynthesis (GPP), transpiration (LE), sap flux (Js)) using data from a natural bottomland hardwood swamp in eastern North Carolina. NEECH4 fluxes were measured over five years (2012 – 2016) that included both wet and dry years. During the growing season, strong cospectral peaks at diurnal scale were detected between CH4 efflux and GPP, LE and Js. This suggests that the well understood diurnal cycles in the latter processes may affect CH4 production through substrate availability (GPP) and transport (sap flow and LE). The causality between different time series was established by the magnitude and consistency of phase shifts. The causal effect of Ts5 and Pa were ruled out because despite cospectral peaks with CH4, their phase relationships were inconsistent. The effect of fluctuations in WTD on CH4 efflux at synoptic scale lacked clear indications of causality, possibly due to time lags and hysteresis. The stronger cospectral peak with ecosystem scale LE rather than Js suggested that the evaporative component of LE contributed equally with plant transpiration. Hence, we conclude that while the emission of dissolved gases through plants likely takes place, it may not contribute to higher CH4 emissions as has been proposed by aerenchymatous gas transport in sedge wetlands. These findings can inform future model development by (i) highlighting the coupling between vegetation processes and CH4 emissions, and (ii) identifying specific and non-overlapping timescales for different driving factors.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Mitra, Bhaskar and Minick, Kevan and Miao, Guofang and Domec, Jean-Christophe and Prajapati, Prajaya and McNulty, Steve G. and Sun, Ge and King, John S. and Noormets, Asko}, year={2020}, month={Sep} }
 @article{mitra_miao_minick_mcnulty_sun_gavazzi_king_noormets_2019, title={Disentangling the Effects of Temperature, Moisture, and Substrate Availability on Soil CO2 Efflux}, volume={124}, ISSN={["2169-8961"]}, DOI={10.1029/2019JG005148}, abstractNote={Abstract}, number={7}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES}, author={Mitra, Bhaskar and Miao, Guofang and Minick, Kevan and McNulty, Steve G. and Sun, Ge and Gavazzi, Michael and King, John S. and Noormets, Asko}, year={2019}, month={Jul}, pages={2060–2075} }
 @article{minick_kelley_miao_li_noormets_mitra_king_2019, title={Microtopography Alters Hydrology, Phenol Oxidase Activity and Nutrient Availability in Organic Soils of a Coastal Freshwater Forested Wetland}, volume={39}, ISSN={["1943-6246"]}, DOI={10.1007/s13157-018-1107-5}, number={2}, journal={WETLANDS}, author={Minick, Kevan J. and Kelley, Alexia M. and Miao, Guofang and Li, Xuefeng and Noormets, Asko and Mitra, Bhaskar and King, John S.}, year={2019}, month={Apr}, pages={263–273} }
 @article{minick_mitra_noormets_king_2019, title={Saltwater reduces potential CO2 and CH4 production in peat soils from a coastal freshwater forested wetland}, volume={16}, ISSN={["1726-4189"]}, DOI={10.5194/bg-16-4671-2019}, abstractNote={Abstract. A major concern for coastal freshwater wetland function
and health is the effects of saltwater intrusion on greenhouse gas
production from peat soils. Coastal freshwater forested wetlands are likely
to experience increased hydroperiod with rising sea level, as well as
saltwater intrusion. These potential changes to wetland hydrology may also
alter forested wetland structure and lead to a transition from forest to
shrub/marsh wetland ecosystems. Loss of forested wetlands is already evident
by dying trees and dead standing trees (“ghost” forests) along the
Atlantic coast of the US, which will result in significant alterations to
plant carbon (C) inputs, particularly that of coarse woody debris, to soils.
We investigated the effects of salinity and wood C inputs on soils collected
from a coastal freshwater forested wetland in North Carolina, USA, and
incubated in the laboratory with either freshwater or saltwater (2.5 or 5.0 ppt) and with or without the additions of wood. Saltwater additions at 2.5 and 5.0 ppt reduced CO2 production by 41 % and 37 %, respectively,
compared to freshwater. Methane production was reduced by 98 % (wood-free
incubations) and by 75 %–87 % (wood-amended incubations) in saltwater
treatments compared to the freshwater plus wood treatment. Additions of wood
also resulted in lower CH4 production from the freshwater treatment and
higher CH4 production from saltwater treatments compared to wood-free
incubations. The δ13CH4-C isotopic signature suggested
that, in wood-free incubations, CH4 produced from the freshwater
treatment originated primarily from the acetoclastic pathway, while CH4
produced from the saltwater treatments originated primarily from the
hydrogenotrophic pathway. These results suggest that saltwater intrusion
into coastal freshwater forested wetlands will reduce CH4 production,
but long-term changes in C dynamics will likely depend on how changes in
wetland vegetation and microbial function influence C cycling in peat soils.
                    }, number={23}, journal={BIOGEOSCIENCES}, author={Minick, Kevan J. and Mitra, Bhaskar and Noormets, Asko and King, John S.}, year={2019}, month={Dec}, pages={4671–4686} }
 @article{lin_domec_ward_marshall_kin_laviner_fox_west_sun_mcnulty_et al._2019, title={Using delta C-13 and delta O-18 to analyze loblolly pine (Pinus taeda L.) response to experimental drought and fertilization}, volume={39}, ISSN={["1758-4469"]}, DOI={10.1093/treephys/tpz096}, abstractNote={Abstract}, number={12}, journal={TREE PHYSIOLOGY}, author={Lin, Wen and Domec, Jean-Christophe and Ward, Eric J. and Marshall, John and Kin, John S. and Laviner, Marshall A. and Fox, Thomas R. and West, Jason B. and Sun, Ge and McNulty, Steve and et al.}, year={2019}, month={Dec}, pages={1984–1994} }
 @article{minick_mitra_li_noormets_king_2019, title={Water Table Drawdown Alters Soil and Microbial Carbon Pool Size and Isotope Composition in Coastal Freshwater Forested Wetlands}, volume={2}, ISSN={["2624-893X"]}, DOI={10.3389/ffgc.2019.00007}, abstractNote={Loss of coastal wetlands is occurring at an increasingly rapid rate due to drainage of these wetlands for alternative land-uses, which also threatens carbon (C) storage in these C-rich ecosystems. Wetland drainage results in water table drawdown and increased peat aeration, which enhances decomposition of previously stabilized peat and changes stable C isotope profiles with soil depth. The effect of water table drawdown on the pool size and δ13C signature of plant C, soil organic C (SOC) and microbial biomass C (MBC) across a range of organic and mineral soils has not previously been reported in coastal freshwater forested wetlands. To this end, litter, roots, and soils were collected from organic and mineral soil horizons in two coastal freshwater forested wetlands in North Carolina with different hydrological regimes: 1) a natural bottomland hardwood forest (natural); and 2) a ditched and drained, intensively-managed wetland for loblolly pine silviculture (managed). We found that hydrology and soil horizon, and to a lesser degree micro-topography, was important in shaping observed differences in size and 13C signature of soil and microbial pools between the natural and managed wetland. The natural wetland had higher SOC and MBC concentrations in the litter, surface organic, and mineral horizons compared to the managed wetland. In the managed wetland, 13C of SOC was enriched across most of the soil profile (Oa and mineral soil horizons) compared to the natural wetland, suggesting enhanced decomposition and incorporation of microbially-derived inputs to soils. Root C concentration decreased with soil depth, while root 13C signature became enriched with soil depth. In the litter and Oe horizon of the natural wetland, MBC was higher and 13C of MBC and SOC was enriched in hummocks compared to hollows. The 13C of MBC and SOC tended to be enriched in upper soil horizons and depleted in lower soil horizons, particularly in the managed wetland. We conclude that drainage of these coastal wetlands has enhanced the breakdown of previously stabilized C and has the potential to alter regional C storage, feedbacks to climate warming, and ecosystem responses to changing environmental conditions.}, journal={FRONTIERS IN FORESTS AND GLOBAL CHANGE}, author={Minick, Kevan J. and Mitra, Bhaskar and Li, Xuefeng and Noormets, Asko and King, John S.}, year={2019}, month={Apr} }
 @article{panda_amatya_jackson_sun_noormets_2018, title={Automated Geospatial Models of Varying Complexities for Pine Forest Evapotranspiration Estimation with Advanced Data Mining}, volume={10}, ISSN={["2073-4441"]}, DOI={10.3390/w10111687}, abstractNote={The study goal was to develop automated user-friendly remote-sensing based evapotranspiration (ET) estimation tools: (i) artificial neural network (ANN) based models, (ii) ArcGIS-based automated geospatial model, and (iii) executable software to predict pine forest daily ET flux on a pixel- or plot average-scale. Study site has had long-term eddy-flux towers for ET measurements since 2006. Cloud-free Landsat images of 2006−2014 were processed using advanced data mining to obtain Principal Component bands to correlate with ET data. The regression model’s r2 was 0.58. The backpropagation neural network (BPNN) and radial basis function network (RBFN) models provided a testing/validation average absolute error of 0.18 and 0.15 Wm−2 and average accuracy of 81% and 85%, respectively. ANN models though robust, require special ANN software and skill to operate; therefore, automated geospatial model (toolbox) was developed on ArcGIS ModelBuilder as user-friendly alternative. ET flux map developed with model tool provided consistent ET patterns for landuses. The software was developed for lay-users for ET estimation.}, number={11}, journal={WATER}, author={Panda, Sudhanshu and Amatya, Devendra M. and Jackson, Rhett and Sun, Ge and Noormets, Asko}, year={2018}, month={Nov} }
 @article{bracho_vogel_will_noormets_samuelson_jokela_gonzalez-benecke_gezan_markewitz_seiler_et al._2018, title={Carbon accumulation in loblolly pine plantations is increased by fertilization across a soil moisture availability gradient}, volume={424}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2018.04.029}, abstractNote={Silvicultural practices, particularly fertilization, may counteract or accentuate the effects of climate change on carbon cycling in planted pine ecosystems, but few studies have empirically assessed the potential effects. In the southeastern United States, we established a factorial throughfall reduction (D) × fertilization (F) experiment in 2012 in four loblolly pine (Pinus taeda L.) plantations encompassing the climatic range of the species in Florida (FL), Georgia (GA), Oklahoma (OK), and Virginia (VA). Net primary productivity (NPP) was estimated from tree inventories for four consecutive years, and net ecosystem productivity (NEP) as NPP minus heterotrophic respiration (RH). Soil respiration (RS) was measured biweekly-monthly for at least one year at each site and simultaneous measurements of RS & RH were taken five to eight times through the year for at least one year during the experiment. Reducing throughfall by 30% decreased available soil water at the surface and for the 0–90 cm soil profile. Fertilization increased NPP at all sites and D decreased NPP (to a lesser extent) at the GA and OK sites. The F + D treatment did not affect NPP. Mean annual NPP under F ranged from 10.01 ± 0.21 MgC·ha−1·yr−1 at VA (mean ± SE) to 17.20 ± 0.50 MgC·ha−1·yr−1 at FL, while the lowest levels were under the D treatment, ranging from 8.63 ± 0.21 MgC·ha−1·yr−1 at VA to 14.97 ± 0.50 MgC·ha−1·yr−1 at FL. RS and RH were, in general, decreased by F and D with differential responses among sites, leading to NEP increases under F. Throughfall reduction increased NEP at FL and VA due to a negative effect on RH and no effect on NPP. Mean annual NEP ranged from 1.63 ± 0.59 MgC·ha−1·yr−1 in the control at OK to 8.18 ± 0.82 MgC·ha−1·yr−1 under F + D at GA. These results suggest that fertilization will increase NEP under a wide range of climatic conditions including reduced precipitation, but either NPP or RH could be the primary driver because F can increase stand growth, as well as suppress RS and RH. Moreover, D and F never significantly interacted for an annual C flux, potentially simplifying estimates of how fertilization and drought will affect C cycling in these ecosystems.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Bracho, Rosvel and Vogel, Jason G. and Will, Rodney E. and Noormets, Asko and Samuelson, Lisa J. and Jokela, Eric J. and Gonzalez-Benecke, Carlos A. and Gezan, Salvador A. and Markewitz, Daniel and Seiler, John R. and et al.}, year={2018}, month={Sep}, pages={39–52} }
 @article{liu_sun_mitra_noormets_gavazzi_domec_hallema_li_fang_king_et al._2018, title={Drought and thinning have limited impacts on evapotranspiration in a managed pine plantation on the southeastern United States coastal plain}, volume={262}, ISSN={0168-1923}, url={http://dx.doi.org/10.1016/j.agrformet.2018.06.025}, DOI={10.1016/j.agrformet.2018.06.025}, abstractNote={Managed and natural coastal plain forests in the humid southeastern United States exchange large amounts of water and energy with the atmosphere through the evapotranspiration (ET) process. ET plays an important role in controlling regional hydrology, climate, and ecosystem productivity. However, long-term studies on the impacts of forest management and climatic variability on forest ET are rare, and our understanding of both external and internal drivers on seasonal and interannual ET variability is incomplete. Using techniques centered on an eddy covariance method, the present study measured year-round ET flux and associated hydrometeorological variables in a drained loblolly pine (Pinus taeda L.) plantation on the lower coastal plain of North Carolina, U.S. We found that annual ET was relatively stable (1076 ± 104 mm) in comparison to precipitation (P) (1168 ± 216 mm) during the 10-year study period when the site experienced extreme climate (2007–2008) and forest thinning (2009). At the seasonal time scale, mean ET/P varied between 0.41 and 1.51, with a mean value of 1.12 ± 0.23 and 0.72 ± 0.16 for the growing and dormant seasons, respectively. The extreme drought during 2007–2008 (mean annual P, 854 mm) only resulted in a slight decrease (∼8%) in annual ET owing to the shallow groundwater common to the study area. Although changes in leaf area index and canopy structure were large after the stand was 50% thinned in the fall of 2009, mean annual ET was similar and averaged 1055 mm and 1104 mm before (2005, 2006 and 2009) and after (2010–2015) thinning, respectively. Data suggested that annual ET recovered within two years of the thinning as a result of rapid canopy closure and growth of understory. Further analysis indicated that available energy was the key driver of ET: approximately 69% and 61% of the monthly variations in ET were explained by net radiation during the dormant and growing seasons, respectively. Overall, we concluded that drought and forest thinning had limited impacts on seasonal and annual ET in this energy limited forest ecosystem with shallow groundwater. The results from this study help to better understand regional ecohydrological processes and projecting potential effects of forest management and extreme climate on water and carbon cycles.}, journal={Agricultural and Forest Meteorology}, publisher={Elsevier BV}, author={Liu, Xiaodong and Sun, Ge and Mitra, Bhaskar and Noormets, Asko and Gavazzi, Michael J. and Domec, Jean-Christophe and Hallema, Dennis W. and Li, Jiyue and Fang, Yuan and King, John S. and et al.}, year={2018}, month={Nov}, pages={14–23} }
 @article{besnard_carvalhais_arain_black_bruin_buchmann_cescatti_chen_clevers_desai_et al._2018, title={Quantifying the effect of forest age in annual net forest carbon balance}, volume={13}, ISSN={["1748-9326"]}, DOI={10.1088/1748-9326/aaeaeb}, abstractNote={Forests dominate carbon (C) exchanges between the terrestrial biosphere and the atmosphere on land. In the long term, the net carbon flux between forests and the atmosphere has been significantly impacted by changes in forest cover area and structure due to ecological disturbances and management activities. Current empirical approaches for estimating net ecosystem productivity (NEP) rarely consider forest age as a predictor, which represents variation in physiological processes that can respond differently to environmental drivers, and regrowth following disturbance. Here, we conduct an observational synthesis to empirically determine to what extent climate, soil properties, nitrogen deposition, forest age and management influence the spatial and interannual variability of forest NEP across 126 forest eddy-covariance flux sites worldwide. The empirical models explained up to 62% and 71% of spatio-temporal and across-site variability of annual NEP, respectively. An investigation of model structures revealed that forest age was a dominant factor of NEP spatio-temporal variability in both space and time at the global scale as compared to abiotic factors, such as nutrient availability, soil characteristics and climate. These findings emphasize the importance of forest age in quantifying spatio-temporal variation in NEP using empirical approaches.}, number={12}, journal={ENVIRONMENTAL RESEARCH LETTERS}, author={Besnard, Simon and Carvalhais, Nuno and Arain, M. Altaf and Black, Andrew and Bruin, Sytze and Buchmann, Nina and Cescatti, Alessandro and Chen, Jiquan and Clevers, Jan G. P. W. and Desai, Ankur R. and et al.}, year={2018}, month={Dec} }
 @article{zhang_li_sun_miao_noormets_emanuel_king_2018, title={Understanding coastal wetland hydrology with a new regional-scale, process-based hydrological model}, volume={32}, ISSN={["1099-1085"]}, url={http://dx.doi.org/10.1002/hyp.13247}, DOI={10.1002/hyp.13247}, abstractNote={Abstract}, number={20}, journal={HYDROLOGICAL PROCESSES}, author={Zhang, Yu and Li, Wenhong and Sun, Ge and Miao, Guofang and Noormets, Asko and Emanuel, Ryan and King, John S.}, year={2018}, month={Sep}, pages={3158–3173} }
 @article{colombo_celesti_bianchi_campbell_cogliati_cook_corp_damm_domec_guanter_et al._2018, title={Variability of sun-induced chlorophyll fluorescence according to stand age-related processes in a managed loblolly pine forest}, volume={24}, ISSN={["1365-2486"]}, DOI={10.1111/gcb.14097}, abstractNote={Abstract}, number={7}, journal={GLOBAL CHANGE BIOLOGY}, author={Colombo, Roberto and Celesti, Marco and Bianchi, Remo and Campbell, Petya K. E. and Cogliati, Sergio and Cook, Bruce D. and Corp, Lawrence A. and Damm, Alexander and Domec, Jean-Christophe and Guanter, Luis and et al.}, year={2018}, month={Jul}, pages={2980–2996} }
 @article{lin_noormets_king_sun_mcnulty_domec_2017, title={An extractive removal step optimized for a high-throughput alpha-cellulose extraction method for delta C-13 and delta O-18 stable isotope ratio analysis in conifer tree rings}, volume={37}, ISSN={["1758-4469"]}, DOI={10.1093/treephys/tpw084}, abstractNote={Stable isotope ratios (δ13C and δ18O) of tree-ring α-cellulose are important tools in paleoclimatology, ecology, plant physiology and genetics. The Multiple Sample Isolation System for Solids (MSISS) was a major advance in the tree-ring α-cellulose extraction methods, offering greater throughput and reduced labor input compared to traditional alternatives. However, the usability of the method for resinous conifer species may be limited by the need to remove extractives from some conifer species in a separate pretreatment step. Here we test the necessity of pretreatment for α-cellulose extraction in loblolly pine (Pinus taeda L.), and the efficiency of a modified acetone-based ambient-temperature step for the removal of extractives (i) in loblolly pine from five geographic locations representing its natural range in the southeastern USA, and (ii) on five other common coniferous species (black spruce (Picea mariana Mill.), Fraser fir (Abies fraseri (Pursh) Poir.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), Norway spruce (Picea abies (L.) Karst) and ponderosa pine (Pinus ponderosa D.)) with contrasting extractive profiles. The differences of δ13C values between the new and traditional pretreatment methods were within the precision of the isotope ratio mass spectrometry method used (±0.2‰), and the differences between δ18O values were not statistically significant. Although some unanticipated results were observed in Fraser fir, the new ambient-temperature technique was deemed as effective as the more labor-consuming and toxic traditional pretreatment protocol. The proposed technique requires a separate acetone-inert multiport system similar to MSISS, and the execution of both pretreatment and main extraction steps allows for simultaneous treatment of up to several hundred microsamples from resinous softwood, while the need of additional labor input remains minimal.}, number={1}, journal={TREE PHYSIOLOGY}, author={Lin, Wen and Noormets, Asko and King, John S. and Sun, Ge and McNulty, Steve and Domec, Jean-Christophe}, year={2017}, month={Jan}, pages={142–150} }
 @article{yang_anderson_gao_hain_semmens_kustas_noormets_wynne_thomas_sun_2017, title={Daily Landsat-scale evapotranspiration estimation over a forested landscape in North Carolina, USA, using multi-satellite data fusion}, volume={21}, ISSN={["1607-7938"]}, DOI={10.5194/hess-21-1017-2017}, abstractNote={Abstract. As a primary flux in the global water cycle, evapotranspiration (ET) connects hydrologic and biological processes and is directly affected by water and land management, land use change and climate variability. Satellite remote sensing provides an effective means for diagnosing ET patterns over heterogeneous landscapes; however, limitations on the spatial and temporal resolution of satellite data, combined with the effects of cloud contamination, constrain the amount of detail that a single satellite can provide. In this study, we describe an application of a multi-sensor ET data fusion system over a mixed forested/agricultural landscape in North Carolina, USA, during the growing season of 2013. The fusion system ingests ET estimates from the Two-Source Energy Balance Model (TSEB) applied to thermal infrared remote sensing retrievals of land surface temperature from multiple satellite platforms: hourly geostationary satellite data at 4 km resolution, daily 1 km imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) and biweekly Landsat thermal data sharpened to 30 m. These multiple ET data streams are combined using the Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM) to estimate daily ET at 30 m resolution to investigate seasonal water use behavior at the level of individual forest stands and land cover patches. A new method, also exploiting the STARFM algorithm, is used to fill gaps in the Landsat ET retrievals due to cloud cover and/or the scan-line corrector (SLC) failure on Landsat 7. The retrieved daily ET time series agree well with observations at two AmeriFlux eddy covariance flux tower sites in a managed pine plantation within the modeling domain: US-NC2 located in a mid-rotation (20-year-old) loblolly pine stand and US-NC3 located in a recently clear-cut and replanted field site. Root mean square errors (RMSEs) for NC2 and NC3 were 0.99 and 1.02 mm day−1, respectively, with mean absolute errors of approximately 29 % at the daily time step, 12 % at the monthly time step and 0.7 % over the full study period at the two flux tower sites. Analyses of water use patterns over the plantation indicate increasing seasonal ET with stand age for young to mid-rotation stands up to 20 years, but little dependence on age for older stands. An accounting of consumptive water use by major land cover classes representative of the modeling domain is presented, as well as relative partitioning of ET between evaporation (E) and transpiration (T) components obtained with the TSEB. The study provides new insights about the effects of management and land use change on water yield over forested landscapes.
                    }, number={2}, journal={HYDROLOGY AND EARTH SYSTEM SCIENCES}, author={Yang, Yun and Anderson, Martha C. and Gao, Feng and Hain, Christopher R. and Semmens, Kathryn A. and Kustas, William P. and Noormets, Asko and Wynne, Randolph H. and Thomas, Valerie A. and Sun, Ge}, year={2017}, month={Feb}, pages={1017–1037} }
 @article{liu_sun_mcnulty_noormets_fang_2017, title={Environmental controls on seasonal ecosystem evapotranspiration/potential evapotranspiration ratio as determined by the global eddy flux measurements}, volume={21}, ISSN={["1607-7938"]}, DOI={10.5194/hess-21-311-2017}, abstractNote={Abstract. The evapotranspiration / potential evapotranspiration (AET / PET) ratio is traditionally termed as the crop coefficient (Kc) and has been generally used as ecosystem evaporative stress index. In the current hydrology literature, Kc has been widely used as a parameter to estimate crop water demand by water managers but has not been well examined for other types of ecosystems such as forests and other perennial vegetation. Understanding the seasonal dynamics of this variable for all ecosystems is important for projecting the ecohydrological responses to climate change and accurately quantifying water use at watershed to global scales. This study aimed at deriving monthly Kc for multiple vegetation cover types and understanding its environmental controls by analyzing the accumulated global eddy flux (FLUXNET) data. We examined monthly Kc data for seven vegetation covers, including open shrubland (OS), cropland (CRO), grassland (GRA), deciduous broad leaf forest (DBF), evergreen needle leaf forest (ENF), evergreen broad leaf forest (EBF), and mixed forest (MF), across 81 sites. We found that, except for evergreen forests (EBF and ENF), Kc values had large seasonal variation across all land covers. The spatial variability of Kc was well explained by latitude, suggesting site factors are a major control on Kc. Seasonally, Kc increased significantly with precipitation in the summer months, except in EBF. Moreover, leaf area index (LAI) significantly influenced monthly Kc in all land covers, except in EBF. During the peak growing season, forests had the highest Kc values, while croplands (CRO) had the lowest. We developed a series of multivariate linear monthly regression models for Kc by land cover type and season using LAI, site latitude, and monthly precipitation as independent variables. The Kc models are useful for understanding water stress in different ecosystems under climate change and variability as well as for estimating seasonal ET for large areas with mixed land covers.
                    }, number={1}, journal={HYDROLOGY AND EARTH SYSTEM SCIENCES}, author={Liu, Chunwei and Sun, Ge and McNulty, Steven G. and Noormets, Asko and Fang, Yuan}, year={2017}, month={Jan}, pages={311–322} }
 @article{miao_noormets_domec_fuentes_trettin_sun_mcnulty_king_2017, title={Hydrology and microtopography control carbon dynamics in wetlands: Implications in partitioning ecosystem respiration in a coastal plain forested wetland}, volume={247}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2017.08.022}, abstractNote={Wetlands store a disproportionately large fraction of organic carbon relative to their areal coverage, and thus play an important role in global climate mitigation. As destabilization of these stores through land use or environmental change represents a significant climate feedback, it is important to understand the functional regulation of respiratory processes that catabolize them. In this study, we established an eddy covariance flux tower project in a coastal plain forested wetland in North Carolina, USA, and measured total ecosystem respiration (Re) over three years (2009–2011). We evaluated the magnitude and variability of three respiration components – belowground (Rs), coarse woody debris (RCWD), and aboveground plant (Ragp) respiration at the ecosystem scale, by accounting microtopographic variation for upscaling and constraining the mass balance with Re. Strong hydrologic control was detected for Rs and RCWD, whereas Ragp and Re were relatively insensitive to water table fluctuations. In a relatively dry year (2010), this forested wetland respired a total of about 2000 g CO2-C m-2 y-1 annually, 51% as Rs, 37% as Ragp, and 12% as RCWD. During non-flooded periods Rs contributed up to 57% of Re and during flooded periods Ragp contributed up to 69%. The contribution of Rs to Re increased by 2.4% for every cm of decrease in water level at intermediate water table level, and was nearly constant when flooded or when the water level more than 15 cm below ground. The contrasting sensitivity of different respiration components highlights the need for explicit consideration of this dynamic in ecosystem and Earth System Models.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Miao, Guofang and Noormets, Asko and Domec, Jean-Christophe and Fuentes, Montserrat and Trettin, Carl C. and Sun, Ge and McNulty, Steve G. and King, John S.}, year={2017}, month={Dec}, pages={343–355} }
 @article{domec_ashley_fischer_noormets_boone_williamson_king_2017, title={Productivity, Biomass Partitioning, and Energy Yield of Low-Input Short-Rotation American Sycamore (Platanus occidentalis L.) Grown on Marginal Land: Effects of Planting Density and Simulated Drought}, volume={10}, ISSN={["1939-1242"]}, DOI={10.1007/s12155-017-9852-5}, number={3}, journal={BIOENERGY RESEARCH}, author={Domec, Jean-Christophe and Ashley, Elissa and Fischer, Milan and Noormets, Asko and Boone, Jameson and Williamson, James C. and King, John S.}, year={2017}, month={Sep}, pages={903–914} }
 @article{ward_domec_king_sun_mcnulty_noormets_2017, title={TRACC: an open source software for processing sap flux data from thermal dissipation probes}, volume={31}, ISSN={["1432-2285"]}, DOI={10.1007/s00468-017-1556-0}, abstractNote={TRACC is an open-source software for standardizing the cleaning, conversion, and calibration of sap flux density data from thermal dissipation probes, which addresses issues of nighttime transpiration and water storage. Thermal dissipation probes (TDPs) have become a widely used method of monitoring plant water use in recent years. The use of TDPs requires calibration to a theoretical zero-flow value (∆T 0); usually based upon the assumption that at least some nighttime measurements represent zero-flow conditions. Fully automating the processing of data from TDPs is made exceedingly difficult due to errors arising from many sources. However, it is desirable to minimize variation arising from different researchers’ processing data, and thus, a common platform for processing data, including editing raw data and determination of ∆T 0, is useful and increases the transparency and replicability of TDP-based research. Here, we present the TDP data processing software TRACC (Thermal dissipation Review Assessment Cleaning and Conversion) to serve this purpose. TRACC is an open-source software written in the language R, using graphical presentation of data and on screen prompts with yes/no or simple numerical responses. It allows the user to select several important options, such as calibration coefficients and the exclusion of nights when vapor pressure deficit does not approach zero. Although it is designed for users with no coding experience, the outputs of TRACC could be easily incorporated into more complex models or software.}, number={5}, journal={TREES-STRUCTURE AND FUNCTION}, author={Ward, Eric J. and Domec, Jean-Christophe and King, John and Sun, Ge and McNulty, Steve and Noormets, Asko}, year={2017}, month={Oct}, pages={1737–1742} }
 @article{middleton_rascher_corp_huemmrich_cook_noormets_schickling_pinto_alonso_damm_et al._2017, title={The 2013 FLEX-US Airborne Campaign at the Parker Tract Loblolly Pine Plantation in North Carolina, USA}, volume={9}, ISSN={["2072-4292"]}, DOI={10.3390/rs9060612}, abstractNote={The first European Space Agency (ESA) and NASA collaboration in an airborne campaign to support ESA’s FLuorescence EXplorer (FLEX) mission was conducted in North Carolina, USA during September–October 2013 (FLEX-US 2013) at the Parker Tract Loblolly Pine (LP) Plantation (Plymouth, NC, USA). This campaign combined two unique airborne instrument packages to obtain simultaneous observations of solar-induced fluorescence (SIF), LiDAR-based canopy structural information, visible through shortwave infrared (VSWIR) reflectance spectra, and surface temperature, to advance vegetation studies of carbon cycle dynamics and ecosystem health. We obtained statistically significant results for fluorescence, canopy temperature, and tower fluxes from data collected at four times of day over two consecutive autumn days across an age class chronosequence. Both the red fluorescence (F685) and far-red fluorescence (F740) radiances had highest values at mid-day, but their fluorescence yields exhibited different diurnal responses across LP age classes. The diurnal trends for F685 varied with forest canopy temperature difference (canopy minus air), having a stronger daily amplitude change for young vs. old canopies. The Photochemical Reflectance Index (PRI) was positively correlated with this temperature variable over the diurnal cycle. Tower measurements from mature loblolly stand showed the red/far-red fluorescence ratio was linearly related to canopy light use efficiency (LUE) over the diurnal cycle, but performed even better for the combined morning/afternoon (without midday) observations. This study demonstrates the importance of diurnal observations for interpretation of fluorescence dynamics, the need for red fluorescence to understand canopy physiological processes, and the benefits of combining fluorescence, reflectance, and structure information to clarify canopy function versus structure characteristics for a coniferous forest.}, number={6}, journal={REMOTE SENSING}, author={Middleton, Elizabeth M. and Rascher, Uwe and Corp, Lawrence A. and Huemmrich, K. Fred and Cook, Bruce D. and Noormets, Asko and Schickling, Anke and Pinto, Francisco and Alonso, Luis and Damm, Alexander and et al.}, year={2017}, month={Jun} }
 @article{gamon_huemmrich_wong_ensminger_garrity_hollinger_noormets_penuelas_2016, title={A remotely sensed pigment index reveals photosynthetic phenology in evergreen conifers}, volume={113}, ISSN={["0027-8424"]}, DOI={10.1073/pnas.1606162113}, abstractNote={Significance}, number={46}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Gamon, John A. and Huemmrich, K. Fred and Wong, Christopher Y. S. and Ensminger, Ingo and Garrity, Steven and Hollinger, David Y. and Noormets, Asko and Penuelas, Josep}, year={2016}, month={Nov}, pages={13087–13092} }
 @article{yao_liang_li_liu_chen_zhang_jia_jiang_xie_munier_et al._2016, title={Assessment and simulation of global terrestrial latent heat flux by synthesis of CMIP5 climate models and surface eddy covariance observations}, volume={223}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2016.03.016}, abstractNote={The latent heat flux (LE) between the terrestrial biosphere and atmosphere is a major driver of the global hydrological cycle. In this study, we evaluated LE simulations by 45 general circulation models (GCMs) in the Coupled Model Intercomparison Project Phase 5 (CMIP5) by a comparison with eddy covariance (EC) observations from 240 globally distributed sites from 2000 to 2009. In addition, we improved global terrestrial LE estimates for different land cover types by synthesis of seven best CMIP5 models and EC observations based on a Bayesian model averaging (BMA) method. The comparison results showed substantial differences in monthly LE among all GCMs. The model CESM1-CAM5 has the best performance with the highest predictive skill and a Taylor skill score (S) from 0.51–0.75 for different land cover types. The cross-validation results illustrate that the BMA method has improved the accuracy of the CMIP5 GCM's LE simulation with a decrease in the averaged root-mean-square error (RMSE) by more than 3 W/m2 when compared to the simple model averaging (SMA) method and individual GCMs. We found an increasing trend in the BMA-based global terrestrial LE (slope of 0.018 W/m2 yr−1, p < 0.05) during the period 1970–2005. This variation may be attributed directly to the inter-annual variations in air temperature (Ta), surface incident solar radiation (Rs) and precipitation (P). However, our study highlights a large difference from previous studies in a continuous increasing trend after 1998, which may be caused by the combined effects of the variations of Rs, Ta, and P on LE for different models on these time scales. This study provides corrected-modeling evidence for an accelerated global water cycle with climate change.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Yao, Yunjun and Liang, Shunlin and Li, Xianglan and Liu, Shaomin and Chen, Jiquan and Zhang, Xiaotong and Jia, Kun and Jiang, Bo and Xie, Xianhong and Munier, Simon and et al.}, year={2016}, month={Jun}, pages={151–167} }
 @article{liu_zhuang_he_noormets_chen_gu_2016, title={Evaluating atmospheric CO2 effects on gross primary productivity and net ecosystem exchanges of terrestrial ecosystems in the conterminous United States using the AmeriFlux data and an artificial neural network approach}, volume={220}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2016.01.007}, abstractNote={Quantitative understanding of regional gross primary productivity (GPP) and net ecosystem exchanges (NEE) and their responses to environmental changes are critical to quantifying the feedbacks of ecosystems to the global climate system. Numerous studies have used the eddy flux data to upscale the eddy covariance derived carbon fluxes from stand scales to regional and global scales. However, few studies incorporated atmospheric carbon dioxide (CO2) concentrations into those extrapolations. Here, we consider the effect of atmospheric CO2 using an artificial neural network (ANN) approach to upscale the AmeriFlux tower of NEE and the derived GPP to the conterminous United States. Two ANN models incorporating remote sensing variables at an 8-day time step were developed. One included CO2 as an explanatory variable and the other did not. The models were first trained, validated using eddy flux data, and then extrapolated to the region at a 0.05o × 0.05o (latitude × longitude) resolution from 2001 to 2006. We found that both models performed well in simulating site-level carbon fluxes. The spatially-averaged annual GPP with and without considering the atmospheric CO2 were 789 and 788 g C m−2 yr−1, respectively (for NEE, the values were −112 and −109 g C m−2 yr−1, respectively). Model predictions were comparable with previous published results and MODIS GPP products. However, the difference in GPP between the two models exhibited a great spatial and seasonal variability, with an annual difference of 200 g C m−2 yr−1. Further analysis suggested that air temperature played an important role in determining the atmospheric CO2 effects on carbon fluxes. In addition, the simulation that did not consider atmospheric CO2 failed to detect ecosystem responses to droughts in part of the US in 2006. The study suggests that the spatially and temporally varied atmospheric CO2 concentrations should be factored into carbon quantification when scaling eddy flux data to a region.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Liu, Shaoqing and Zhuang, Qianlai and He, Yujie and Noormets, Asko and Chen, Jiquan and Gu, Lianhong}, year={2016}, month={Apr}, pages={38–49} }
 @article{fang_sun_caldwell_mcnulty_noormets_domec_king_zhang_zhang_lin_et al._2016, title={Monthly land cover-specific evapotranspiration models derived from global eddy flux measurements and remote sensing data}, volume={9}, ISSN={["1936-0592"]}, DOI={10.1002/eco.1629}, abstractNote={Abstract}, number={2}, journal={ECOHYDROLOGY}, author={Fang, Yuan and Sun, Ge and Caldwell, Peter and McNulty, Steven G. and Noormets, Asko and Domec, Jean-Christophe and King, John and Zhang, Zhiqiang and Zhang, Xudong and Lin, Guanghui and et al.}, year={2016}, month={Mar}, pages={248–266} }
 @article{gonzalez-benecke_teskey_martin_jokela_fox_kane_noormets_2016, title={Regional validation and improved parameterization of the 3-PG model for Pinus taeda stands}, volume={361}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2015.11.025}, abstractNote={The forest simulation model, 3-PG, has the capability to estimate the effects of climate, site and management practices on many stand attributes using easily available data. The model, once calibrated, has been widely applied as a useful tool for estimating growth of forest species in many countries. Currently, there is an increasing interest in estimating biomass and assessing the potential impact of climate change on loblolly pine (Pinus taeda L.), the most important commercial tree species in the southeastern U.S. This paper reports a new set of 3-PG parameter estimates for loblolly pine, and describe new methodologies to determine important estimates. Using data from the literature and long-term productivity studies, we parameterized 3-PG for loblolly pine stands, and developed new functions for estimating NPP allocation dynamics, biomass pools at variable starting ages, canopy cover dynamics, effects of frost on production, density-independent and density-dependent tree mortality and the fertility rating. The model was tested against data from replicated experimental measurement plots covering a wide range of stand characteristics, distributed across the southeastern U.S. and also beyond the natural range of the species, using stands in Uruguay, South America. We used the largest validation dataset for 3-PG, and the most geographically extensive within and beyond a species’ native range. Comparison of modeled to measured data showed robust agreement across the natural range in the U.S., as well as in South America, where the species is grown as an exotic. Across all tested sites, estimations of survival, basal area, height, quadratic mean diameter, bole volume and above-ground biomass agreed well with measured values, with R2 values ranging between 0.71 for bole volume, and 0.95 for survival. The levels of bias were small and generally less than 13%. LAI estimations performed well, predicting monthly values within the range of observed LAI. The results provided strong evidence that 3-PG could be applied over a wide geographical range using one set of parameters for loblolly pine. The model can also be applied to estimate the impact of climate change on stands growing across a wide range of ages and stand characteristics.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Gonzalez-Benecke, Carlos A. and Teskey, Robert O. and Martin, Timothy A. and Jokela, Eric J. and Fox, Thomas R. and Kane, Michael B. and Noormets, Asko}, year={2016}, month={Feb}, pages={237–256} }
 @article{manoli_domec_novick_oishi_noormets_marani_katul_2016, title={Soil-plant-atmosphere conditions regulating convective cloud formation above southeastern US pine plantations}, volume={22}, ISSN={["1365-2486"]}, DOI={10.1111/gcb.13221}, abstractNote={Abstract}, number={6}, journal={GLOBAL CHANGE BIOLOGY}, author={Manoli, Gabriele and Domec, Jean-Christophe and Novick, Kimberly and Oishi, Andrew Christopher and Noormets, Asko and Marani, Marco and Katul, Gabriel}, year={2016}, month={Jun}, pages={2238–2254} }
 @article{novick_ficklin_stoy_williams_bohrer_oishi_papuga_blanken_noormets_sulman_et al._2016, title={The increasing importance of atmospheric demand for ecosystem water and carbon fluxes}, volume={6}, ISSN={["1758-6798"]}, DOI={10.1038/nclimate3114}, abstractNote={During periods of hydrologic stress, vegetation productivity is limited by soil moisture supply and atmospheric water demand. This study shows that atmospheric demand has a greater effect in many biomes, with implications for climate change impacts. Soil moisture supply and atmospheric demand for water independently limit—and profoundly affect—vegetation productivity and water use during periods of hydrologic stress1,2,3,4. Disentangling the impact of these two drivers on ecosystem carbon and water cycling is difficult because they are often correlated, and experimental tools for manipulating atmospheric demand in the field are lacking. Consequently, the role of atmospheric demand is often not adequately factored into experiments or represented in models5,6,7. Here we show that atmospheric demand limits surface conductance and evapotranspiration to a greater extent than soil moisture in many biomes, including mesic forests that are of particular importance to the terrestrial carbon sink8,9. Further, using projections from ten general circulation models, we show that climate change will increase the importance of atmospheric constraints to carbon and water fluxes in all ecosystems. Consequently, atmospheric demand will become increasingly important for vegetation function, accounting for >70% of growing season limitation to surface conductance in mesic temperate forests. Our results suggest that failure to consider the limiting role of atmospheric demand in experimental designs, simulation models and land management strategies will lead to incorrect projections of ecosystem responses to future climate conditions.}, number={11}, journal={NATURE CLIMATE CHANGE}, author={Novick, Kimberly A. and Ficklin, Darren L. and Stoy, Paul C. and Williams, Christopher A. and Bohrer, Gil and Oishi, A. Christopher and Papuga, Shirley A. and Blanken, Peter D. and Noormets, Asko and Sulman, Benjamin N. and et al.}, year={2016}, month={Nov}, pages={1023–1027} }
 @article{will_fox_akers_domec_gonzalez-benecke_jokela_kane_laviner_lokuta_markewitz_et al._2015, title={A Range-Wide Experiment to Investigate Nutrient and Soil Moisture Interactions in Loblolly Pine Plantations}, volume={6}, ISSN={["1999-4907"]}, DOI={10.3390/f6062014}, abstractNote={The future climate of the southeastern USA is predicted to be warmer, drier and more variable in rainfall, which may increase drought frequency and intensity. Loblolly pine (Pinus taeda) is the most important commercial tree species in the world and is planted on ~11 million ha within its native range in the southeastern USA. A regional study was installed to evaluate effects of decreased rainfall and nutrient additions on loblolly pine plantation productivity and physiology. Four locations were established to capture the range-wide variability of soil and climate. Treatments were initiated in 2012 and consisted of a factorial combination of throughfall reduction (approximate 30% reduction) and fertilization (complete suite of nutrients). Tree and stand growth were measured at each site. Results after two growing seasons indicate a positive but variable response of fertilization on stand volume increment at all four sites and a negative effect of throughfall reduction at two sites. Data will be used to produce robust process model parameterizations useful for simulating loblolly pine growth and function under future, novel climate and management scenarios. The resulting improved models will provide support for developing management strategies to increase pine plantation productivity and carbon sequestration under a changing climate.}, number={6}, journal={FORESTS}, author={Will, Rodney E. and Fox, Thomas and Akers, Madison and Domec, Jean-Christophe and Gonzalez-Benecke, Carlos and Jokela, Eric J. and Kane, Michael and Laviner, Marshall A. and Lokuta, Geoffrey and Markewitz, Daniel and et al.}, year={2015}, month={Jun}, pages={2014–2028} }
 @article{domec_king_ward_oishi_palmroth_radecki_bell_miao_gavazzi_johnson_et al._2015, title={Conversion of natural forests to managed forest plantations decreases tree resistance to prolonged droughts}, volume={355}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2015.04.012}, abstractNote={Throughout the southern US, past forest management practices have replaced large areas of native forests with loblolly pine plantations and have resulted in changes in forest response to extreme weather conditions. However, uncertainty remains about the response of planted versus natural species to drought across the geographical range of these forests. Taking advantage of a cluster of unmanaged stands (85–130 year-old hardwoods) and managed plantations (17–20 year-old loblolly pine) in coastal and Piedmont areas of North Carolina, tree water use, cavitation resistance, whole-tree hydraulic (Ktree) and stomatal (Gs) conductances were measured in four sites covering representative forests growing in the region. We also used a hydraulic model to predict the resilience of those sites to extreme soil drying. Our objectives were to determine: (1) if Ktree and stomatal regulation in response to atmospheric and soil droughts differ between species and sites; (2) how ecosystem type, through tree water use, resistance to cavitation and rooting profiles, affects the water uptake limit that can be reached under drought; and (3) the influence of stand species composition on critical transpiration that sets a functional water uptake limit under drought conditions. The results show that across sites, water stress affected the coordination between Ktree and Gs. As soil water content dropped below 20% relative extractable water, Ktree declined faster and thus explained the decrease in Gs and in its sensitivity to vapor pressure deficit. Compared to branches, the capability of roots to resist high xylem tension has a great impact on tree-level water use and ultimately had important implications for pine plantations resistance to future summer droughts. Model simulations revealed that the decline in Ktree due to xylem cavitation aggravated the effects of soil drying on tree transpiration. The critical transpiration rate (Ecrit), which corresponds to the maximum rate at which transpiration begins to level off to prevent irreversible hydraulic failure, was higher in managed forest plantations than in their unmanaged counterparts. However, even with this higher Ecrit, the pine plantations operated very close to their critical leaf water potentials (i.e. to their permissible water potentials without total hydraulic failure), suggesting that intensively managed plantations are more drought-sensitive and can withstand less severe drought than natural forests.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Domec, Jean-Christophe and King, John S. and Ward, Eric and Oishi, A. Christopher and Palmroth, Sari and Radecki, Andrew and Bell, Dave M. and Miao, Guofang and Gavazzi, Michael and Johnson, Daniel M. and et al.}, year={2015}, month={Nov}, pages={58–71} }
 @misc{noormets_epron_domec_mcnulty_fox_sun_king_2015, title={Effects of forest management on productivity and carbon sequestration: A review and hypothesis}, volume={355}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2015.05.019}, abstractNote={With an increasing fraction of the world’s forests being intensively managed for meeting humanity’s need for wood, fiber and ecosystem services, quantitative understanding of the functional changes in these ecosystems in comparison with natural forests is needed. In particular, the role of managed forests as long-term carbon (C) sinks and for mitigating climate change require a detailed assessment of their carbon cycle on different temporal scales. In the current review we assess available data on the structure and function of the world’s forests, explore the main differences in the C exchange between managed and unmanaged stands, and explore potential physiological mechanisms behind both observed and expected changes. Two global databases that include classification for management indicate that managed forests are about 50 years younger, include 25% more coniferous stands, and have about 50% lower C stocks than unmanaged forests. The gross primary productivity (GPP) and total net primary productivity (NPP) are the similar, but relatively more of the assimilated carbon is allocated to aboveground pools in managed than in unmanaged forests, whereas allocation to fine roots and rhizosymbionts is lower. This shift in allocation patterns is promoted by increasing plant size, and by increased nutrient availability. Long-term carbon sequestration potential in soils is assessed through the ratio of heterotrophic respiration to total detritus production, which indicates that (i) the forest soils may be losing more carbon on an annual basis than they regain in detritus, and (ii) the deficit appears to be greater in managed forests. While climate change and management factors (esp. fertilization) both contribute to greater carbon accumulation potential in the soil, the harvest-related increase in decomposition affects the C budget over the entire harvest cycle. Although the findings do not preclude the use of forests for climate mitigation, maximizing merchantable productivity may have significant carbon costs for the soil pool. We conclude that optimal management strategies for maximizing multiple benefits from ecosystem services require better understanding of the dynamics of belowground allocation, carbohydrate availability, heterotrophic respiration, and carbon stabilization in the soil.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Noormets, A. and Epron, D. and Domec, J. C. and McNulty, S. G. and Fox, T. and Sun, G. and King, J. S.}, year={2015}, month={Nov}, pages={124–140} }
 @article{kang_zhang_noormets_fang_zha_zhou_sun_mcnulty_chen_2015, title={Energy partitioning and surface resistance of a poplar plantation in northern China}, volume={12}, ISSN={["1726-4189"]}, DOI={10.5194/bg-12-4245-2015}, abstractNote={Abstract. Poplar (Populus sp.) plantations have been, on the one hand, broadly used in northern China for urban greening, combating desertification, as well as for paper and wood production. On the other hand, such plantations have been questioned occasionally for their possible negative impacts on water availability due to the higher water-use nature of poplar trees compared with other tree species in water-limited dryland regions. To further understand the acclimation of poplar species to semiarid environments and to evaluate the potential impacts of these plantations on the broader context of the region's water supply, we examine the variability of bulk resistance parameters and energy partitioning in a poplar (Populus euramericana cv. "74/76") plantation located in northern China over a 4-year period, encompassing both dry and wet conditions. The partitioning of available energy to latent heat flux (LE) decreased from 0.62 to 0.53 under mediated meteorological drought by irrigation applications. A concomitant increase in sensible heat flux (H) resulted in the increase of a Bowen ratio from 0.83 to 1.57. Partial correlation analysis indicated that surface resistance (Rs) normalized by leaf area index (LAI; Rs:LAI) increased by 50 % under drought conditions and was the dominant factor controlling the Bowen ratio. Furthermore, Rs was the main factor controlling LE during the growing season, even in wet years, as indicated by the decoupling coefficient (Ω = 0.45 and 0.39 in wet and dry years, respectively). Rs was also a major regulator of the LE / LEeq ratio, which decreased from 0.81 in wet years to 0.68 in dry years. All physiological and bioclimatological metrics indicated that the water demands of the poplar plantation were greater than the amount available through precipitation, highlighting the poor match of a water-intensive species like poplar for this water-limited region.
                    }, number={14}, journal={BIOGEOSCIENCES}, author={Kang, M. and Zhang, Z. and Noormets, A. and Fang, X. and Zha, T. and Zhou, J. and Sun, G. and McNulty, S. G. and Chen, J.}, year={2015}, pages={4245–4259} }
 @article{ward_domec_laviner_fox_sun_mcnulty_king_noormets_2015, title={Fertilization intensifies drought stress: Water use and stomatal conductance of Pinus taeda in a midrotation fertilization and throughfall reduction experiment}, volume={355}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2015.04.009}, abstractNote={While mid-rotation fertilization increases productivity in many southern pine forests, it remains unclear what impact such management may have on stand water use. We examined the impact of nutrient and water availability on stem volume, leaf area, transpiration per unit ground area (EC) and canopy conductance per unit leaf area (GS) of a pine plantation during its 8th and 9th growing seasons. Treatments consisted of a factorial combination of throughfall reduction (30% reduction in throughfall versus ambient) and fertilization (a complete suite of essential nutrients) beginning in April 2012. Overall, our results indicate that despite unusually high rainfall in the study period and a lack of leaf area index (LAI) response, both EC and GS decreased in response to fertilization and throughfall reduction. Fertilization increased stem volume increment 21% in 2013. Treatment differences were greatest in the growing season of 2013, when EC was on average 19%, 13% and 29% lower in the throughfall reduction (D), fertilization (F) and combined treatment (FD) than the control (C), respectively. The responses of GS to volumetric soil water content (VWC) indicate that lower EC in F was associated with a decrease relative to C in GS at high VWC. Decreases of GS in D relative to C were associated with lower VWC, but little change in the response of GS to VWC. Decreases observed in FD resulted from a combination of these two factors. The pattern of GS responses in the different treatments suggests that structural or physiological changes underlie this fertilization response, possibly in fine root area or hydraulic conductivity. In the short term, this led to large increases in the water use efficiency of stem production, which could suggest greater resiliency to minor water stress. However, impacts on long-term sensitivity to drought remain a concern, as the EC reduction triggered by the fertilization treatment was of comparable magnitude to the 30% throughfall exclusion treatment and the greatest reductions were found in the combined treatment.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Ward, Eric J. and Domec, Jean-Christophe and Laviner, Marshall A. and Fox, Thomas R. and Sun, Ge and McNulty, Steve and King, John and Noormets, Asko}, year={2015}, month={Nov}, pages={72–82} }
 @article{noormets_nouvellon_2015, title={Introduction for special issue: Carbon, water and nutrient cycling in managed forests}, volume={355}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2015.08.022}, abstractNote={The global forest carbon (C) stock is estimated at 662 Gt of which 45% is in soil organic matter. Thus, comprehensive understanding of the effects of forest management practices on forest soil C stock and greenhouse gas (GHG) fluxes is needed for the development of effective forest-based climate change mitigation strategies. To improve this understanding, we synthesized peer-reviewed literature on forest management practices that can mitigate climate change by increasing soil C stocks and reducing GHG emissions. We further identified soil processes that affect soil GHG balance and discussed how models represent forest management effects on soil in GHG inventories and scenario analyses to address forest climate change mitigation potential.Forest management effects depend strongly on the specific practice and land type. Intensive timber harvesting with removal of harvest residues/stumps results in a reduction in soil C stock, while high stocking density and enhanced productivity by fertilization or dominance of coniferous species increase soil C stock. Nitrogen fertilization increases the soil C stock and N2O emissions while decreasing the CH4 sink. Peatland hydrology management is a major driver of the GHG emissions of the peatland forests, with lower water level corresponding to higher CO2 emissions. Furthermore, the global warming potential of all GHG emissions (CO2, CH4 and N2O) together can be ten-fold higher after clear-cutting than in peatlands with standing trees.The climate change mitigation potential of forest soils, as estimated by modelling approaches, accounts for stand biomass driven effects and climate factors that affect the decomposition rate. A future challenge is to account for the effects of soil preparation and other management that affects soil processes by changing soil temperature, soil moisture, soil nutrient balance, microbial community structure and processes, hydrology and soil oxygen concentration in the models. We recommend that soil monitoring and modelling focus on linking processes of soil C stabilization with the functioning of soil microbiota.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Noormets, A. and Nouvellon, Y.}, year={2015}, month={Nov}, pages={1–3} }
 @article{wu_ju_zhou_he_law_black_margolis_cescatti_gu_montagnani_et al._2015, title={Performance of Linear and Nonlinear Two-Leaf Light Use Efficiency Models at Different Temporal Scales}, volume={7}, ISSN={["2072-4292"]}, DOI={10.3390/rs70302238}, abstractNote={The reliable simulation of gross primary productivity (GPP) at various spatial and temporal scales is of significance to quantifying the net exchange of carbon between terrestrial ecosystems and the atmosphere. This study aimed to verify the ability of a nonlinear two-leaf model (TL-LUEn), a linear two-leaf model (TL-LUE), and a big-leaf light use efficiency model (MOD17) to simulate GPP at half-hourly, daily and 8-day scales using GPP derived from 58 eddy-covariance flux sites in Asia, Europe and North America as benchmarks. Model evaluation showed that the overall performance of TL-LUEn was slightly but not significantly better than TL-LUE at half-hourly and daily scale, while the overall performance of both TL-LUEn and TL-LUE were significantly better (p < 0.0001) than MOD17 at the two temporal scales. The improvement of TL-LUEn over TL-LUE was relatively small in comparison with the improvement of TL-LUE over MOD17. However, the differences between TL-LUEn and MOD17, and TL-LUE and MOD17 became less distinct at the 8-day scale. As for different vegetation types, TL-LUEn and TL-LUE performed better than MOD17 for all vegetation types except crops at the half-hourly scale. At the daily and 8-day scales, both TL-LUEn and TL-LUE outperformed MOD17 for forests. However, TL-LUEn had a mixed performance for the three non-forest types while TL-LUE outperformed MOD17 slightly for all these non-forest types at daily and 8-day scales. The better performance of TL-LUEn and TL-LUE for forests was mainly achieved by the correction of the underestimation/overestimation of GPP simulated by MOD17 under low/high solar radiation and sky clearness conditions. TL-LUEn is more applicable at individual sites at the half-hourly scale while TL-LUE could be regionally used at half-hourly, daily and 8-day scales. MOD17 is also an applicable option regionally at the 8-day scale.}, number={3}, journal={REMOTE SENSING}, author={Wu, Xiaocui and Ju, Weimin and Zhou, Yanlian and He, Mingzhu and Law, Beverly E. and Black, T. Andrew and Margolis, Hank A. and Cescatti, Alessandro and Gu, Lianhong and Montagnani, Leonardo and et al.}, year={2015}, month={Mar}, pages={2238–2278} }
 @article{tian_youssef_sun_chescheir_noormets_amatya_skaggs_king_mcnulty_gavazzi_et al._2015, title={Testing DRAINMOD-FOREST for predicting evapotranspiration in a mid-rotation pine plantation}, volume={355}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2015.03.028}, abstractNote={Evapotranspiration (ET) is a key component of the hydrologic cycle in terrestrial ecosystems and accurate description of ET processes is essential for developing reliable ecohydrological models. This study investigated the accuracy of ET prediction by the DRAINMOD-FOREST after its calibration/validation for predicting commonly measured hydrological variables. The model was tested by conducting an eight year simulation of drainage and shallow groundwater dynamics in a managed mid-rotation loblolly pine (Pinus taeda L.) plantation located in the coastal plain of North Carolina, USA. Modeled daily ET rates were compared to those measured in the field using the eddy covariance technique. In addition, the wavelet transform and coherence analysis were used to compare ET predictions and measurements on the time–frequency domain. Results showed that DRAINMOD-FOREST accurately predicted annual and monthly ET after a successful calibration and validation using measured drainage rates and water table depth. The model under predicted ET on an annual basis by 2%, while the Nash–Sutcliffe coefficient of model predictions on a monthly basis was 0.78. Results from wavelet transform and coherence analysis demonstrated that the model reasonably captured the high power spectra of ET at an annual scale with significantly high model-data coherency. These results suggested that the calibrated DRAINMOD-FOREST collectively captured key factors and mechanisms controlling ET dynamics in the drained pine plantation. However, the global power spectrum revealed that the model over predicted the power spectrum of ET at an annual scale, suggesting the model may have under predicted canopy conductance during non-growing seasons. In addition, this study also suggested that DRAINMOD-FOREST did not properly capture the seasonal dynamics of ET under extreme drought conditions with deeper water table depths. These results suggested further refinement to parameters, particularly vegetation related, and structures of DRAINMOD-FOREST to achieve better agreement between ET predictions and measurements in the time–frequency domain.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Tian, Shiying and Youssef, Mohamed A. and Sun, Ge and Chescheir, George M. and Noormets, Asko and Amatya, Devendra M. and Skaggs, R. Wayne and King, John S. and McNulty, Steve and Gavazzi, Michael and et al.}, year={2015}, month={Nov}, pages={37–47} }
 @article{zhang_song_sun_band_noormets_zhang_2015, title={Understanding moisture stress on light use efficiency across terrestrial ecosystems based on global flux and remote-sensing data}, volume={120}, ISSN={["2169-8961"]}, DOI={10.1002/2015jg003023}, abstractNote={Abstract}, number={10}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES}, author={Zhang, Yulong and Song, Conghe and Sun, Ge and Band, Lawrence E. and Noormets, Asko and Zhang, Quanfa}, year={2015}, month={Oct}, pages={2053–2066} }
 @article{song_niu_luo_luo_chen_yu_olejnik_wohlfahrt_kiely_noormets_et al._2014, title={Divergent apparent temperature sensitivity of terrestrial ecosystem respiration}, volume={7}, ISSN={["1752-993X"]}, DOI={10.1093/jpe/rtu014}, abstractNote={Aims Recent studies revealed convergent temperature sensitivity of ecosystem respiration (Re) within aquatic ecosystems and between terrestrial and aquatic ecosystems. We do not know yet whether various terrestrial ecosystems have consistent or divergent temperature sensitivity. Here, we synthesized 163 eddy covariance flux sites across the world and examined the global variation of the apparent activation energy (Ea), which characterizes the apparent temperature sensitivity of and its interannual variability (IAV) as well as their controlling factors. Methods We used carbon fluxes and meteorological data across FLUXNET sites to calculate mean annual temperature, temperature range, precipitation, global radiation, potential radiation, gross primary productivity and Re by averaging the daily values over the years in each site. Furthermore, we analyzed the sites with >8 years data to examine the IAV of Ea and calculated the standard deviation of Ea across years at each site to characterize IAV. Important Findings The results showed a widely global variation of Ea, with significantly lower values in the tropical and subtropical areas than in temperate and boreal areas, and significantly higher values in grasslands and wetlands than that in deciduous broadleaf forests and evergreen forests. Globally, spatial variations of Ea were explained by changes in temperature and an index of water availability with differing contribution of each explaining variable among climate zones and biomes. IAV and the corresponding coefficient of variation of Ea decreased with increasing latitude, but increased with radiation and corresponding mean annual temperature. The revealed patterns in the spatial and temporal variations of Ea and its controlling factors indicate divergent temperature sensitivity of R-e, which could help to improve our predictive understanding of R-e in response to climate change.}, number={5}, journal={JOURNAL OF PLANT ECOLOGY}, author={Song, Bing and Niu, Shuli and Luo, Ruisen and Luo, Yiqi and Chen, Jiquan and Yu, Guirui and Olejnik, Janusz and Wohlfahrt, Georg and Kiely, Gerard and Noormets, Asko and et al.}, year={2014}, month={Oct}, pages={419–428} }
 @article{xie_chen_sun_chu_noormets_ouyang_john_wan_guan_2014, title={Long-term variability and environmental control of the carbon cycle in an oak-dominated temperate forest}, volume={313}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2013.10.032}, abstractNote={Our understanding of the long-term carbon (C) cycle of temperate deciduous forests and its sensitivity to climate variability is limited due to the large temporal dynamics of C fluxes. The goal of the study was to quantify the effects of environmental variables on the C balance in a 70-year-old mixed-oak woodland forest over a 7-year period in northwest Ohio, USA. The net ecosystem exchanges (NEE) of C were measured using the eddy-covariance technique. Long-term mean NEE, ecosystem respiration (ER), and gross ecosystem productivity (GEP) were −339 ± 34, 1213 ± 84, and 1552 ± 82 g C m−2 year−1, respectively. Warming increased ER more than GEP when the available water was not limited, but decreased GEP more than ER when the available water was limited, resulting in decreasing net C fluxes under both conditions. The decreasing net C sink in summer was associated with increasing air temperature (Ta) in spring. The leaf area index (LAI), photosynthetically-active radiation (PAR), and Ta were the most important determinants of NEE for spring, summer, and winter, respectively; however, these variables failed to explain NEE for autumn. The most important determinants of ER and GEP were soil temperature (Ts) in spring, Ta and PAR in summer, and Ta in autumn. Ta was the only control of ER in winter. The annual variation in NEE was larger than that of GEP or ER. The controls of GEP on NEE were more pronounced seasonally and annually than those of ER. The annual GEP was consistently more variable than the annual ER. GEP was also seasonally and annually correlated with ER. Practical models derived from different combinations of independent variables effectively predicted 87%, 80%, and 93% of the monthly variability in NEE, ER, and GEP, respectively. We concluded that the variability in C fluxes was more responsive to increasing Ta and Ts than to variations in seasonal and annual precipitation. The study implies that a warmer climate is likely to reduce the forest productivity and C-sink capacity of oak ecosystems in the future, especially in instances when water inputs become limiting.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Xie, Jing and Chen, Jiquan and Sun, Ge and Chu, Housen and Noormets, Asko and Ouyang, Zutao and John, Ranjeet and Wan, Shiqiang and Guan, Wenbin}, year={2014}, month={Feb}, pages={319–328} }
 @article{xie_sun_chu_liu_mcnulty_noormets_john_ouyang_zha_li_et al._2014, title={Long-term variability in the water budget and its controls in an oak-dominated temperate forest}, volume={28}, ISSN={["1099-1085"]}, DOI={10.1002/hyp.10079}, abstractNote={Water availability is one of the key environmental factors that control ecosystem functions in temperate forests. Changing climate is likely to alter the ecohydrology and other ecosystem processes, which affect forest structures and functions. We constructed a multi‐year water budget (2004–2010) and quantified environmental controls on an evapotranspiration (ET) in a 70‐year‐old mixed‐oak woodland forest in northwest Ohio, USA. ET was measured using the eddy‐covariance technique along with precipitation (P), soil volumetric water content (VWC), and shallow groundwater table fluctuation. Three biophysical models were constructed and validated to calculate potential ET (PET) for developing predictive monthly ET models. We found that the annual variability in ET was relatively stable and ranged from 578 mm in 2009 to 670 mm in 2010. In contrast, ET/P was more variable and ranged from 0.60 in 2006 to 0.96 in 2010. Mean annual ET/PET_FAO was 0.64, whereas the mean annual PET_FAO/P was 1.15. Annual ET/PET_FAO was relatively stable and ranged from 0.60 in 2005 to 0.72 in 2004. Soil water storage and shallow groundwater recharge during the non‐growing season were essential in supplying ET during the growing season when ET exceeded P. Spring leaf area index (LAI), summer photosynthetically active radiation, and autumn and winter air temperatures (Ta) were the most significant controls of monthly ET. Moreover, LAI regulated ET during the whole growing season and higher temperatures increased ET even during dry periods. Our empirical modelling showed that the interaction of LAI and PET explained >90% of the variability in measured ET. Altogether, we found that increases in Ta and shifts in P distribution are likely to impact forest hydrology by altering shallow groundwater fluctuations, soil water storage, and ET and, consequently, alter the ecosystem functions of temperate forests. Copyright © 2013 John Wiley & Sons, Ltd.}, number={25}, journal={HYDROLOGICAL PROCESSES}, author={Xie, Jing and Sun, Ge and Chu, Hou-Sen and Liu, Junguo and McNulty, Steven G. and Noormets, Asko and John, Ranjeet and Ouyang, Zutao and Zha, Tianshan and Li, Haitao and et al.}, year={2014}, month={Dec}, pages={6054–6066} }
 @article{wang_xiao_ollinger_desai_chen_noormets_2014, title={Quantifying the effects of harvesting on carbon fluxes and stocks in northern temperate forests}, volume={11}, ISSN={["1726-4189"]}, DOI={10.5194/bg-11-6667-2014}, abstractNote={Abstract. Harvest disturbance has substantial impacts on forest carbon (C) fluxes and stocks. The quantification of these effects is essential for the better understanding of forest C dynamics and informing forest management in the context of global change. We used a process-based forest ecosystem model, PnET-CN, to evaluate how, and by what mechanisms, clear-cuts alter ecosystem C fluxes, aboveground C stocks (AGC), and leaf area index (LAI) in northern temperate forests. We compared C fluxes and stocks predicted by the model and observed at two chronosequences of eddy covariance flux sites for deciduous broadleaf forests (DBF) and evergreen needleleaf forests (ENF) in the Upper Midwest region of northern Wisconsin and Michigan, USA. The average normalized root mean square error (NRMSE) and the Willmott index of agreement (d) for carbon fluxes, LAI, and AGC in the two chronosequences were 20% and 0.90, respectively. Simulated gross primary productivity (GPP) increased with stand age, reaching a maximum (1200–1500 g C m−2 yr−1) at 11–30 years of age, and leveled off thereafter (900–1000 g C m−2 yr−1). Simulated ecosystem respiration (ER) for both plant functional types (PFTs) was initially as high as 700–1000 g C m−2 yr−1 in the first or second year after harvesting, decreased with age (400–800 g C m−2 yr−1) before canopy closure at 10–25 years of age, and increased to 800–900 g C m−2 yr−1 with stand development after canopy recovery. Simulated net ecosystem productivity (NEP) for both PFTs was initially negative, with net C losses of 400–700 g C m−2 yr−1 for 6–17 years after clear-cuts, reaching peak values of 400–600 g C m−2 yr−1 at 14–29 years of age, and eventually stabilizing in mature forests (> 60 years old), with a weak C sink (100–200 g C m−2 yr−1). The decline of NEP with age was caused by the relative flattening of GPP and gradual increase of ER. ENF recovered more slowly from a net C source to a net sink, and lost more C than DBF. This suggests that in general ENF may be slower to recover to full C assimilation capacity after stand-replacing harvests, arising from the slower development of photosynthesis with stand age. Our model results indicated that increased harvesting intensity would delay the recovery of NEP after clear-cuts, but this had little effect on C dynamics during late succession. Future modeling studies of disturbance effects will benefit from the incorporation of forest population dynamics (e.g., regeneration and mortality) and relationships between age-related model parameters and state variables (e.g., LAI) into the model.
                    }, number={23}, journal={BIOGEOSCIENCES}, author={Wang, W. and Xiao, J. and Ollinger, S. V. and Desai, A. R. and Chen, J. and Noormets, A.}, year={2014}, pages={6667–6682} }
 @article{zhou_zhang_sun_fang_zha_chen_noormets_guo_mcnulty_2014, title={Water-use efficiency of a poplar plantation in Northern China}, volume={19}, ISSN={["1610-7403"]}, DOI={10.1007/s10310-014-0436-3}, abstractNote={The water-use efficiency (WUE) of an ecosystem—defined as the gross ecosystem production (GEP) divided by the evapotranspiration (ET)—is an important index for understanding the coupling of water and carbon and quantifying water–carbon trade-offs in forests. An open-path eddy covariance technique and a microclimate measurement system were deployed to investigate the WUE of a poplar plantation ecosystem in the Daxing District of Beijing, China, during the growing seasons in 2006, 2007, and 2008. We found that WUE values changed diurnally, peaking in early morning and showing a minimum between 2 pm and 3 pm. This pattern was regulated by photosynthetically active radiation, saturated vapor pressure deficit, and stomatal opening and closure. WUE had inter-daily variations but no substantial seasonal variation. The WUE decreased with increasing soil water content due to the higher sensitivity of ET than GEP to increased soil moisture. Under moist soil conditions (i.e., relative extractable water content >0.4), GEP was stable and WUE was generally low. These results suggest that the poplar plantation does not effectively use the available soil water for carbon uptake, and that soil moisture is lost to the atmosphere through ET.}, number={6}, journal={JOURNAL OF FOREST RESEARCH}, author={Zhou, Jie and Zhang, Zhiqiang and Sun, Ge and Fang, Xianrui and Zha, Tonggang and Chen, Jiquan and Noormets, Asko and Guo, Junting and McNulty, Steve}, year={2014}, month={Dec}, pages={483–492} }
 @article{olson_griffis_noormets_kolka_chen_2013, title={Interannual, seasonal, and retrospective analysis of the methane and carbon dioxide budgets of a temperate peatland}, volume={118}, ISSN={["2169-8961"]}, DOI={10.1002/jgrg.20031}, abstractNote={Abstract}, number={1}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES}, author={Olson, D. M. and Griffis, T. J. and Noormets, A. and Kolka, R. and Chen, J.}, year={2013}, month={Mar}, pages={226–238} }
 @article{john_chen_noormets_xiao_xu_lu_chen_2013, title={Modelling gross primary production in semi-arid Inner Mongolia using MODIS imagery and eddy covariance data}, volume={34}, ISSN={["1366-5901"]}, DOI={10.1080/01431161.2012.746483}, abstractNote={We evaluate the modelling of carbon fluxes from eddy covariance (EC) tower observations in different water-limited land-cover/land-use (LCLU) and biome types in semi-arid Inner Mongolia, China. The vegetation photosynthesis model (VPM) and modified VPM (MVPM), driven by the enhanced vegetation index (EVI) and land-surface water index (LSWI), which were derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) surface-reflectance product (MOD09A1), were used to model and validate the temporal changes in gross primary production (GPP) from the EC towers during the 2006 and 2007 growing seasons. The annual GPP predicted by the VPM model (GPPVPM) was predicted reasonably well in 2006 and 2007 at the cropland (coefficient of determination, R 2 = 0.67 and 0.71, for 2006 and 2007, respectively) and typical steppe (R 2 = 0.80 and 0.73) sites. The predictive power of the VPM model varied in the desert steppe, which includes an irrigated poplar stand (R 2 = 0.74 and 0.68) and shrubland (R 2 = 0.31 and 0.49) sites. The comparison between GPP obtained from the eddy covariance tower (GPPtower) and GPP obtained from MVPM (GPPMVPM) (predicted GPP) showed good agreement for the typical steppe site of Xilinhaote (R 2 = 0.84 and 0.70 in 2006 and 2007, respectively) and for the Duolun steppe site (R 2 = 0.63) and cropland site (R 2 = 0.63) in 2007. The predictive power of the MVPM model decreased slightly in the desert steppe at the irrigated poplar stand (R 2 = 0.56 and 0.47 in 2006 and 2007 respectively) and the shrubland (R 2 = 0.20 and 0.41). The results of this study demonstrate the feasibility of modelling GPP from EC towers in semi-arid regions.}, number={8}, journal={INTERNATIONAL JOURNAL OF REMOTE SENSING}, author={John, Ranjeet and Chen, Jiquan and Noormets, Asko and Xiao, Xiangming and Xu, Jianye and Lu, Nan and Chen, Shiping}, year={2013}, month={Apr}, pages={2829–2857} }
 @article{zhou_zhang_sun_fang_zha_mcnulty_chen_jin_noormets_2013, title={Response of ecosystem carbon fluxes to drought events in a poplar plantation in Northern China}, volume={300}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2013.01.007}, abstractNote={Poplar plantations are widely used for timber production and ecological restoration in northern China, a region that experiences frequent droughts and water scarcity. An open-path eddy-covariance (EC) system was used to continuously measure the carbon, water, and energy fluxes in a poplar plantation during the growing season (i.e., April–October) over the period 2006–2008 in the Daxing District of Beijing, China. We examined the seasonal and inter-annual variability of gross ecosystem productivity (GEP), net ecosystem exchange (NEE), and ecosystem respiration (ER). Although annual total precipitation was the lowest in 2006, natural rainfall was amended by flood irrigation. In contrast, no supplementary water was provided during a severe drought in spring (i.e., April–June), 2007, resulting in a significant reduction in net ecosystem production (NEP = −NEE). This resulted from the combined effects of larger decrease in GEP than that in ER. Despite the drought – induced reduction in NEP, the plantation forest was a strong carbon sink accumulating 591 ± 62, 641 ± 71, and 929 ± 75 g C m−2 year−1 for 2006, 2007, and 2008, respectively. The timing of the drought significantly affected the annual GEP. Severe drought during canopy development induced a lasting reduction in carbon exchange throughout the growing season, while the severe drought at the end of growing season did not significantly reduce carbon uptake. Additionally, irrigation reduced negative drought impacts on carbon sequestration. Overall, this fast growing poplar plantation is a strong carbon sink and is sensitive to the changes in environmental conditions.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Zhou, Jie and Zhang, Zhiqiang and Sun, Ge and Fang, Xianrui and Zha, Tonggang and McNulty, Steve and Chen, Jiquan and Jin, Ying and Noormets, Asko}, year={2013}, month={Jul}, pages={33–42} }
 @article{miao_noormets_domec_trettin_mcnulty_sun_king_2013, title={The effect of water table fluctuation on soil respiration in a lower coastal plain forested wetland in the southeastern US}, volume={118}, ISSN={["2169-8961"]}, DOI={10.1002/2013jg002354}, abstractNote={Abstract}, number={4}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES}, author={Miao, Guofang and Noormets, Asko and Domec, Jean-Christophe and Trettin, Carl C. and McNulty, Steve G. and Sun, Ge and King, John S.}, year={2013}, month={Dec}, pages={1748–1762} }
 @article{domec_sun_noormets_gavazzi_treasure_cohen_swenson_mcnulty_king_2012, title={A Comparison of Three Methods to Estimate Evapotranspiration in Two Contrasting Lob lolly Pine Plantations: Age-Related Changes in Water Use and Drought Sensitivity of Evapotranspiration Components}, volume={58}, ISSN={["1938-3738"]}, DOI={10.5849/forsci.11-051}, abstractNote={Increasing variability of rainfall patterns requires detailed understanding of the pathways of water loss from ecosystems to optimize carbon uptake and management choices. In the current study we characterized the usability of three alternative methods of different rigor for quantifying stand-level evapotranspiration (ET), partitioned ET into tree transpiration (T), understory transpiration, interception, and soil evaporation (E S) and determined their sensitivity to drought, and evaluated the reliability of soil moisture measurements by taking into account deep soil moisture dynamic. The analyses were conducted in an early- and in a mid-rotation stand of loblolly pine, the predominant species of southern US forest plantations. The three alternative methods for estimating ET were the eddy covariance measurements of water vapor fluxes (ET EC), the water table fluctuation (ET WT), and the soil moisture fluctuation (ETSM). On annual and monthly scales, the three methods agreed to within 10-20%, whereas on a daily scale, the values of ET SM and ETEC differed by up to 50% and ETSM and ET WT differed by up to 100%. The differences between the methods were attributed to root water extraction below measurement depth and to the sampling at different spatial scales. Regardless of the method used, ET at the early-rotation site was 15-30% lower than that at the mid-rotation site. The dry years did not affect ET at the mid-rotation site but reduced significantly ET at the early-rotation site. Soil moisture trends revealed the importance of measuring water content at several depths throughout the rooting zone because less than 20% of the water is stored in the top 30 cm of soil. Annually, E S represented approximately 9 and 14% of ETEC at the mid-rotation site and the early-rotation site, respectively. At the mid-rotation site, T accounted for approximately 70% of ET EC. Canopy interception was estimated to be 5-10% of annual precipitation and 6-13% of total ETEC. At the early-rotation site, T accounted for only 35% of ET EC. At this site, transpiration from subdominant trees and shrubs represented 40-45% of ET EC, indicating that understory was a significant part of the water budget. We concluded that the eddy covariance method is best for estimating ET at the fine temporal scale (i.e., daily), but other soil moisture and water table-based methods were equally reliable and cost-effective for quantifying seasonal ET dynamics. FOR .S CI. 58(5):497-512.}, number={5}, journal={FOREST SCIENCE}, author={Domec, Jean-Christophe and Sun, Ge and Noormets, Asko and Gavazzi, Michael J. and Treasure, Emrys A. and Cohen, Erika and Swenson, Jennifer J. and McNulty, Steve G. and King, John S.}, year={2012}, month={Oct}, pages={497–512} }
 @article{domec_ogee_noormets_jouangy_gavazzi_treasure_sun_mcnulty_king_2012, title={Interactive effects of nocturnal transpiration and climate change on the root hydraulic redistribution and carbon and water budgets of southern United States pine plantations}, volume={32}, ISSN={["1758-4469"]}, DOI={10.1093/treephys/tps018}, abstractNote={Deep root water uptake and hydraulic redistribution (HR) have been shown to play a major role in forest ecosystems during drought, but little is known about the impact of climate change, fertilization and soil characteristics on HR and its consequences on water and carbon fluxes. Using data from three mid-rotation loblolly pine plantations, and simulations with the process-based model MuSICA, this study indicated that HR can mitigate the effects of soil drying and had important implications for carbon uptake potential and net ecosystem exchange (NEE), especially when N fertilization is considered. At the coastal site (C), characterized by deep organic soil, HR increased dry season tree transpiration (T) by up to 40%, and such an increase affected NEE through major changes in gross primary productivity (GPP). Deep-rooted trees did not necessarily translate into a large volume of HR unless soil texture allowed large water potential gradients to occur, as was the case at the sandy site (S). At the Piedmont site (P) characterized by a shallow clay-loam soil, HR was low but not negligible, representing up to 10% of T. In the absence of HR, it was predicted that at the C, S and P sites, annual GPP would have been diminished by 19, 7 and 9%, respectively. Under future climate conditions HR was predicted to be reduced by up to 25% at the C site, reducing the resilience of trees to precipitation deficits. The effect of HR on T and GPP was predicted to diminish under future conditions by 12 and 6% at the C and P sites, respectively. Under future conditions, T was predicted to stay the same at the P site, but to be marginally reduced at the C site and slightly increased at the S site. Future conditions and N fertilization would decrease T by 25% at the C site, by 15% at the P site and by 8% at the S site. At the C and S sites, GPP was estimated to increase by 18% and by >70% under future conditions, respectively, with little effect of N fertilization. At the P site, future conditions would stimulate GPP by only 12%, but future conditions plus N fertilization would increase GPP by 24%. As a consequence, in all sites, water use efficiency was predicted to improve dramatically with future conditions. Modeling the effect of reduced annual precipitation indicated that limited water availability would decrease all carbon fluxes, including NEE and respiration. Our simulations highlight the interactive effects of nutrients and elevated CO(2), and showed that the effect of N fertilization would be greater under future climate conditions.}, number={6}, journal={TREE PHYSIOLOGY}, author={Domec, Jean-Christophe and Ogee, Jerome and Noormets, Asko and Jouangy, Julien and Gavazzi, Michael and Treasure, Emrys and Sun, Ge and McNulty, Steve G. and King, John S.}, year={2012}, month={Jun}, pages={707–723} }
 @article{noormets_mcnulty_domec_gavazzi_sun_king_2012, title={The role of harvest residue in rotation cycle carbon balance in loblolly pine plantations. Respiration partitioning approach}, volume={18}, ISSN={["1354-1013"]}, DOI={10.1111/j.1365-2486.2012.02776.x}, abstractNote={Abstract}, number={10}, journal={GLOBAL CHANGE BIOLOGY}, author={Noormets, Asko and McNulty, Steve G. and Domec, Jean-Christophe and Gavazzi, Michael and Sun, Ge and King, John S.}, year={2012}, month={Oct}, pages={3186–3201} }
 @article{niu_luo_fei_yuan_schimel_law_ammann_arain_arneth_aubinet_et al._2012, title={Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms}, volume={194}, ISSN={["0028-646X"]}, DOI={10.1111/j.1469-8137.2012.04095.x}, abstractNote={• It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales. • Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of net ecosystem exchange (NEE), an ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms. • We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of ecosystem respiration. • Ecosystem-level thermal optimality is a newly revealed ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within ecosystems, and has the potential to significantly regulate ecosystem-climate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of ecosystems in changing environments and benchmarking global models.}, number={3}, journal={NEW PHYTOLOGIST}, author={Niu, Shuli and Luo, Yiqi and Fei, Shenfeng and Yuan, Wenping and Schimel, David and Law, Beverly E. and Ammann, Christof and Arain, M. Altaf and Arneth, Almut and Aubinet, Marc and et al.}, year={2012}, month={May}, pages={775–783} }
 @article{sun_alstad_chen_chen_ford_lin_liu_lu_mcnulty_miao_et al._2011, title={A general predictive model for estimating monthly ecosystem evapotranspiration}, volume={4}, ISSN={["1936-0592"]}, DOI={10.1002/eco.194}, abstractNote={Abstract}, number={2}, journal={ECOHYDROLOGY}, author={Sun, Ge and Alstad, Karrin and Chen, Jiquan and Chen, Shiping and Ford, Chelcy R. and Lin, Guanghui and Liu, Chenfeng and Lu, Nan and McNulty, Steven G. and Miao, Haixia and et al.}, year={2011}, month={Mar}, pages={245–255} }
 @article{xiao_zhuang_law_baldocchi_chen_richardson_melillo_davis_hollinger_wharton_et al._2011, title={Assessing net ecosystem carbon exchange of U.S. terrestrial ecosystems by integrating eddy covariance flux measurements and satellite observations}, volume={151}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2010.09.002}, abstractNote={More accurate projections of future carbon dioxide concentrations in the atmosphere and associated climate change depend on improved scientific understanding of the terrestrial carbon cycle. Despite the consensus that U.S. terrestrial ecosystems provide a carbon sink, the size, distribution, and interannual variability of this sink remain uncertain. Here we report a terrestrial carbon sink in the conterminous U.S. at 0.63 pg C yr−1 with the majority of the sink in regions dominated by evergreen and deciduous forests and savannas. This estimate is based on our continuous estimates of net ecosystem carbon exchange (NEE) with high spatial (1 km) and temporal (8-day) resolutions derived from NEE measurements from eddy covariance flux towers and wall-to-wall satellite observations from Moderate Resolution Imaging Spectroradiometer (MODIS). We find that the U.S. terrestrial ecosystems could offset a maximum of 40% of the fossil-fuel carbon emissions. Our results show that the U.S. terrestrial carbon sink varied between 0.51 and 0.70 pg C yr−1 over the period 2001–2006. The dominant sources of interannual variation of the carbon sink included extreme climate events and disturbances. Droughts in 2002 and 2006 reduced the U.S. carbon sink by ∼20% relative to a normal year. Disturbances including wildfires and hurricanes reduced carbon uptake or resulted in carbon release at regional scales. Our results provide an alternative, independent, and novel constraint to the U.S. terrestrial carbon sink.}, number={1}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Xiao, Jingfeng and Zhuang, Qianlai and Law, Beverly E. and Baldocchi, Dennis D. and Chen, Jiquan and Richardson, Andrew D. and Melillo, Jerry M. and Davis, Kenneth J. and Hollinger, David Y. and Wharton, Sonia and et al.}, year={2011}, month={Jan}, pages={60–69} }
 @article{sun_caldwell_noormets_mcnulty_cohen_myers_domec_treasure_mu_xiao_et al._2011, title={Upscaling key ecosystem functions across the conterminous United States by a water-centric ecosystem model}, volume={116}, ISSN={["2169-8961"]}, DOI={10.1029/2010jg001573}, abstractNote={[1] We developed a water-centric monthly scale simulation model (WaSSI-C) by integrating empirical water and carbon flux measurements from the FLUXNET network and an existing water supply and demand accounting model (WaSSI). The WaSSI-C model was evaluated with basin-scale evapotranspiration (ET), gross ecosystem productivity (GEP), and net ecosystem exchange (NEE) estimates by multiple independent methods across 2103 eight-digit Hydrologic Unit Code watersheds in the conterminous United States from 2001 to 2006. Our results indicate that WaSSI-C captured the spatial and temporal variability and the effects of large droughts on key ecosystem fluxes. Our modeled mean (±standard deviation in space) ET (556 ± 228 mm yr−1) compared well to Moderate Resolution Imaging Spectroradiometer (MODIS) based (527 ± 251 mm yr−1) and watershed water balance based ET (571 ± 242 mm yr−1). Our mean annual GEP estimates (1362 ± 688 g C m−2 yr−1) compared well (R2 = 0.83) to estimates (1194 ± 649 g C m−2 yr−1) by eddy flux-based EC-MOD model, but both methods led significantly higher (25–30%) values than the standard MODIS product (904 ± 467 g C m−2 yr−1). Among the 18 water resource regions, the southeast ranked the highest in terms of its water yield and carbon sequestration capacity. When all ecosystems were considered, the mean NEE (−353 ± 298 g C m−2 yr−1) predicted by this study was 60% higher than EC-MOD's estimate (−220 ± 225 g C m−2 yr−1) in absolute magnitude, suggesting overall high uncertainty in quantifying NEE at a large scale. Our water-centric model offers a new tool for examining the trade-offs between regional water and carbon resources under a changing environment.}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES}, author={Sun, Ge and Caldwell, Peter and Noormets, Asko and McNulty, Steven G. and Cohen, Erika and Myers, Jennifer Moore and Domec, Jean-Christophe and Treasure, Emrys and Mu, Qiaozhen and Xiao, Jingfeng and et al.}, year={2011}, month={May} }
 @article{xiao_zhuang_law_chen_baldocchi_cook_oren_richardson_wharton_ma_et al._2010, title={A continuous measure of gross primary production for the conterminous United States derived from MODIS and AmeriFlux data}, volume={114}, ISSN={["1879-0704"]}, DOI={10.1016/j.rse.2009.10.013}, abstractNote={The quantification of carbon fluxes between the terrestrial biosphere and the atmosphere is of scientific importance and also relevant to climate-policy making. Eddy covariance flux towers provide continuous measurements of ecosystem-level exchange of carbon dioxide spanning diurnal, synoptic, seasonal, and interannual time scales. However, these measurements only represent the fluxes at the scale of the tower footprint. Here we used remotely sensed data from the Moderate Resolution Imaging Spectroradiometer (MODIS) to upscale gross primary productivity (GPP) data from eddy covariance flux towers to the continental scale. We first combined GPP and MODIS data for 42 AmeriFlux towers encompassing a wide range of ecosystem and climate types to develop a predictive GPP model using a regression tree approach. The predictive model was trained using observed GPP over the period 2000–2004, and was validated using observed GPP over the period 2005–2006 and leave-one-out cross-validation. Our model predicted GPP fairly well at the site level. We then used the model to estimate GPP for each 1 km × 1 km cell across the U.S. for each 8-day interval over the period from February 2000 to December 2006 using MODIS data. Our GPP estimates provide a spatially and temporally continuous measure of gross primary production for the U.S. that is a highly constrained by eddy covariance flux data. Our study demonstrated that our empirical approach is effective for upscaling eddy flux GPP data to the continental scale and producing continuous GPP estimates across multiple biomes. With these estimates, we then examined the patterns, magnitude, and interannual variability of GPP. We estimated a gross carbon uptake between 6.91 and 7.33 Pg C yr− 1 for the conterminous U.S. Drought, fires, and hurricanes reduced annual GPP at regional scales and could have a significant impact on the U.S. net ecosystem carbon exchange. The sources of the interannual variability of U.S. GPP were dominated by these extreme climate events and disturbances.}, number={3}, journal={REMOTE SENSING OF ENVIRONMENT}, author={Xiao, Jingfeng and Zhuang, Qianlai and Law, Beverly E. and Chen, Jiquan and Baldocchi, Dennis D. and Cook, David R. and Oren, Ram and Richardson, Andrew D. and Wharton, Sonia and Ma, Siyan and et al.}, year={2010}, month={Mar}, pages={576–591} }
 @article{lenz_host_roskoski_noormets_sober_karnosky_2010, title={Analysis of a Farquhar-von Caemmerer-Berry leaf-level photosynthetic rate model for Populus tremuloides in the context of modeling and measurement limitations}, volume={158}, ISSN={["1873-6424"]}, DOI={10.1016/j.envpol.2009.08.004}, abstractNote={The balance of mechanistic detail with mathematical simplicity contributes to the broad use of the Farquhar, von Caemmerer and Berry (FvCB) photosynthetic rate model. Here the FvCB model was coupled with a stomatal conductance model to form an [A,gs] model, and parameterized for mature Populus tremuloides leaves under varying CO2 and temperature levels. Data were selected to be within typical forest light, CO2 and temperature ranges, reducing artifacts associated with data collected at extreme values. The error between model-predicted photosynthetic rate (A) and A data was measured in three ways and found to be up to three times greater for each of two independent data sets than for a base-line evaluation using parameterization data. The evaluation methods used here apply to comparisons of model validation results among data sets varying in number and distribution of data, as well as to performance comparisons of [A,gs] models differing in internal-process components.}, number={4}, journal={ENVIRONMENTAL POLLUTION}, author={Lenz, Kathryn E. and Host, George E. and Roskoski, Kyle and Noormets, Asko and Sober, Anu and Karnosky, David F.}, year={2010}, month={Apr}, pages={1015–1022} }
 @article{yi_ricciuto_li_wolbeck_xu_nilsson_aires_albertson_ammann_arain_et al._2010, title={Climate control of terrestrial carbon exchange across biomes and continents}, volume={5}, number={3}, journal={Environmental Research Letters}, author={Yi, C. X. and Ricciuto, D. and Li, R. and Wolbeck, J. and Xu, X. Y. and Nilsson, M. and Aires, L. and Albertson, J. D. and Ammann, C. and Arain, M. A. and et al.}, year={2010} }
 @article{amiro_barr_barr_black_bracho_brown_chen_clark_davis_desai_et al._2010, title={Ecosystem carbon dioxide fluxes after disturbance in forests of North America}, volume={115}, ISSN={["2169-8961"]}, DOI={10.1029/2010jg001390}, abstractNote={Disturbances are important for renewal of North American forests. Here we summarize more than 180 site years of eddy covariance measurements of carbon dioxide flux made at forest chronosequences in North America. The disturbances included stand‐replacing fire (Alaska, Arizona, Manitoba, and Saskatchewan) and harvest (British Columbia, Florida, New Brunswick, Oregon, Quebec, Saskatchewan, and Wisconsin) events, insect infestations (gypsy moth, forest tent caterpillar, and mountain pine beetle), Hurricane Wilma, and silvicultural thinning (Arizona, California, and New Brunswick). Net ecosystem production (NEP) showed a carbon loss from all ecosystems following a stand‐replacing disturbance, becoming a carbon sink by 20 years for all ecosystems and by 10 years for most. Maximum carbon losses following disturbance (g C m−2y−1) ranged from 1270 in Florida to 200 in boreal ecosystems. Similarly, for forests less than 100 years old, maximum uptake (g C m−2y−1) was 1180 in Florida mangroves and 210 in boreal ecosystems. More temperate forests had intermediate fluxes. Boreal ecosystems were relatively time invariant after 20 years, whereas western ecosystems tended to increase in carbon gain over time. This was driven mostly by gross photosynthetic production (GPP) because total ecosystem respiration (ER) and heterotrophic respiration were relatively invariant with age. GPP/ER was as low as 0.2 immediately following stand‐replacing disturbance reaching a constant value of 1.2 after 20 years. NEP following insect defoliations and silvicultural thinning showed lesser changes than stand‐replacing events, with decreases in the year of disturbance followed by rapid recovery. NEP decreased in a mangrove ecosystem following Hurricane Wilma because of a decrease in GPP and an increase in ER.}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES}, author={Amiro, B. D. and Barr, A. G. and Barr, J. G. and Black, T. A. and Bracho, R. and Brown, M. and Chen, J. and Clark, K. L. and Davis, K. J. and Desai, A. R. and et al.}, year={2010}, month={Oct} }
 @article{noormets_kull_sober_kubiske_karnosky_2010, title={Elevated CO2 response of photosynthesis depends on ozone concentration in aspen}, volume={158}, ISSN={["1873-6424"]}, DOI={10.1016/j.envpol.2009.10.009}, abstractNote={The effect of elevated CO2 and O3 on apparent quantum yield (ϕ), maximum photosynthesis (Pmax), carboxylation efficiency (Vcmax) and electron transport capacity (Jmax) at different canopy locations was studied in two aspen (Populus tremuloides) clones of contrasting O3 tolerance. Local light climate at every leaf was characterized as fraction of above-canopy photosynthetic photon flux density (%PPFD). Elevated CO2 alone did not affect ϕ or Pmax, and increased Jmax in the O3-sensitive, but not in the O3-tolerant clone. Elevated O3 decreased leaf chlorophyll content and all photosynthetic parameters, particularly in the lower canopy, and the negative impact of O3 increased through time. Significant interaction effect, whereby the negative impact of elevated O3 was exaggerated by elevated CO2 was seen in Chl, N and Jmax, and occurred in both O3-tolerant and O3-sensitive clones. The clonal differences in the level of CO2 × O3 interaction suggest a relationship between photosynthetic acclimation and background O3 concentration.}, number={4}, journal={ENVIRONMENTAL POLLUTION}, author={Noormets, Asko and Kull, Olevi and Sober, Anu and Kubiske, Mark E. and Karnosky, David F.}, year={2010}, month={Apr}, pages={992–999} }
 @article{sun_noormets_gavazzi_mcnulty_chen_domec_king_amatya_skaggs_2010, title={Energy and water balance of two contrasting loblolly pine plantations on the lower coastal plain of North Carolina, USA}, volume={259}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2009.09.016}, abstractNote={During 2005–2007, we used the eddy covariance and associated hydrometric methods to construct energy and water budgets along a chronosequence of loblolly pine (Pinus taeda) plantations that included a mid-rotation stand (LP) (i.e., 13–15 years old) and a recently established stand on a clearcut site (CC) (i.e., 4–6 years old) in Eastern North Carolina. Our central objective was to quantify the differences in both energy and water balances between the two contrasting stands and understand the underlining mechanisms of environmental controls. We found that the LP site received about 20% more net radiation (Rn) due to its lower averaged albedo (α) of 0.25, compared with that at the CC (α = 0.34). The mean monthly averaged Bowen ratios (β) at the LP site were 0.89 ± 0.7, significantly (p = 0.02) lower than at the CC site (1.45 ± 1.2). Higher net radiation resulted in a 28% higher (p = 0.02) latent heat flux (LE) for ecosystem evapotranspiration at the LP site, but there was no difference in sensible heat flux (H) between the two contrasting sites. The annual total evapotranspiration (ET) at the LP site and CC site was estimated as 1011–1226 and 755–855 mm year−1, respectively. The differences in ET rates between the two contrasting sites occurred mostly during the non-growing seasons and/or dry periods, and they were small during peak growing seasons or wet periods. Higher net radiation and biomass in LP were believed to be responsible to the higher ET. The monthly ET/Grass Reference ET ratios differed significantly across site and season. The annual ET/P ratio for the LP and CC were estimated as 0.70–1.13 and 0.60–0.88, respectively, indicating higher runoff production from the CC site than the LP site. This study implied that reforestation practices reduced surface albedos and thus increased available energy, but they did not necessarily increase energy for warming the atmosphere in the coastal plain region where soil water was generally not limited. This study showed the highly variable response of energy and water balances to forest management due to climatic variability.}, number={7}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Sun, G. and Noormets, A. and Gavazzi, M. J. and McNulty, S. G. and Chen, J. and Domec, J. -C. and King, J. S. and Amatya, D. M. and Skaggs, R. W.}, year={2010}, month={Mar}, pages={1299–1310} }
 @article{noormets_sun_mcnulty_gavazzi_chen_domec_king_amatya_skaggs_2010, title={Energy and water balance of two contrasting loblolly pine plantations on the lower coastal plain of North Carolina, USA (vol 259, pg 1299, 2010)}, volume={260}, number={1}, journal={Forest Ecology and Management}, author={Noormets, A. and Sun, G. and McNulty, S. G. and Gavazzi, M. J. and Chen, J. and Domec, J. C. and King, J. S. and Amatya, D. M. and Skaggs, R. W.}, year={2010}, pages={169–169} }
 @article{domec_king_noormets_treasure_gavazzi_sun_mcnulty_2010, title={Hydraulic redistribution of soil water by roots affects whole-stand evapotranspiration and net ecosystem carbon exchange}, volume={187}, ISSN={["1469-8137"]}, DOI={10.1111/j.1469-8137.2010.03245.x}, abstractNote={
            Commentary p 3
          }, number={1}, journal={NEW PHYTOLOGIST}, author={Domec, Jean-Christophe and King, John S. and Noormets, Asko and Treasure, Emrys and Gavazzi, Michael J. and Sun, Ge and McNulty, Steven G.}, year={2010}, pages={171–183} }
 @article{noormets_gavazzi_mcnulty_domec_sun_king_chen_2010, title={Response of carbon fluxes to drought in a coastal plain loblolly pine forest}, volume={16}, ISSN={["1365-2486"]}, DOI={10.1111/j.1365-2486.2009.01928.x}, abstractNote={Abstract}, number={1}, journal={GLOBAL CHANGE BIOLOGY}, author={Noormets, Asko and Gavazzi, Michael J. and Mcnulty, Steve G. and Domec, Jean-Christophe and Sun, Ge and King, John S. and Chen, Jiquan}, year={2010}, month={Jan}, pages={272–287} }
 @article{domec_noormets_king_sun_mcnulty_gavazzi_boggs_treasure_2009, title={Decoupling the influence of leaf and root hydraulic conductances on stomatal conductance and its sensitivity to vapour pressure deficit as soil dries in a drained loblolly pine plantation}, volume={32}, ISSN={["1365-3040"]}, DOI={10.1111/j.1365-3040.2009.01981.x}, abstractNote={ABSTRACT}, number={8}, journal={PLANT CELL AND ENVIRONMENT}, author={Domec, Jean-Christophe and Noormets, Asko and King, John S. and Sun, Ge and McNulty, Steven G. and Gavazzi, Michael J. and Boggs, Johnny L. and Treasure, Emrys A.}, year={2009}, month={Aug}, pages={980–991} }
 @article{gorsel_delpierre_leuning_black_munger_wofsy_aubinet_feigenwinter_beringer_bonal_et al._2009, title={Estimating nocturnal ecosystem respiration from the vertical turbulent flux and change in storage of CO2}, volume={149}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2009.06.020}, abstractNote={Micrometeorological measurements of nighttime ecosystem respiration can be systematically biased when stable atmospheric conditions lead to drainage flows associated with decoupling of air flow above and within plant canopies. The associated horizontal and vertical advective fluxes cannot be measured using instrumentation on the single towers typically used at micrometeorological sites. A common approach to minimize bias is to use a threshold in friction velocity, u*, to exclude periods when advection is assumed to be important, but this is problematic in situations when in-canopy flows are decoupled from the flow above. Using data from 25 flux stations in a wide variety of forest ecosystems globally, we examine the generality of a novel approach to estimating nocturnal respiration developed by van Gorsel et al. (van Gorsel, E., Leuning, R., Cleugh, H.A., Keith, H., Suni, T., 2007. Nocturnal carbon efflux: reconciliation of eddy covariance and chamber measurements using an alternative to the u*-threshold filtering technique. Tellus 59B, 397–403, Tellus, 59B, 307-403). The approach is based on the assumption that advection is small relative to the vertical turbulent flux (FC) and change in storage (FS) of CO2 in the few hours after sundown. The sum of FC and FS reach a maximum during this period which is used to derive a temperature response function for ecosystem respiration. Measured hourly soil temperatures are then used with this function to estimate respiration RRmax. The new approach yielded excellent agreement with (1) independent measurements using respiration chambers, (2) with estimates using ecosystem light-response curves of Fc + Fs extrapolated to zero light, RLRC, and (3) with a detailed process-based forest ecosystem model, Rcast. At most sites respiration rates estimated using the u*-filter, Rust, were smaller than RRmax and RLRC. Agreement of our approach with independent measurements indicates that RRmax provides an excellent estimate of nighttime ecosystem respiration.}, number={11}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Gorsel, Eva and Delpierre, Nicolas and Leuning, Ray and Black, Andy and Munger, J. William and Wofsy, Steven and Aubinet, Marc and Feigenwinter, Christian and Beringer, Jason and Bonal, Damien and et al.}, year={2009}, month={Nov}, pages={1919–1930} }
 @article{noormets_2009, title={Phenology of ecosystem processes: Applications in global change research}, ISBN={144190025X}, publisher={New York: Springer}, author={Noormets, A.}, year={2009}, pages={275} }
 @article{wilske_lu_wei_chen_zha_liu_xu_noormets_huang_wei_et al._2009, title={Poplar plantation has the potential to alter the water balance in semiarid Inner Mongolia}, volume={90}, ISSN={["1095-8630"]}, DOI={10.1016/j.jenvman.2009.03.004}, abstractNote={Poplar plantation is the most dominant broadleaf forest type in northern China. Since the mid-1990s plantation was intensified to combat desertification along China's northwestern border, i.e., within Inner Mongolia (IM). This evoked much concern regarding the ecological and environmental effects on areas that naturally grow grass or shrub vegetation. To highlight potential consequences of large-scale poplar plantations on the water budget within semiarid IM, we compared the growing season water balance (evapotranspiration (ET) and precipitation (PPT)) of a 3-yr old poplar plantation (Kp3) and a natural shrubland (Ks) in the Kubuqi Desert in western IM, and a 6-yr old poplar plantation (Bp6) growing under sub-humid climate near Beijing. The results showed that, despite 33% lower PPT at Kp3, ET was 2% higher at Kp3 (228 mm) as compared with Ks (223 mm) in May–September 2006. The difference derived mainly from higher ET at the plantation during drier periods of the growing season, which also indicated that the poplars must have partly transpired groundwater. Estimated growing season ET at Bp6 was about 550 mm and more than 100% higher than at Kp3. It is estimated that increases in leaf area index and net radiation at Kp3 provide future potential for the poplars in Kubuqi to exceed the present ET and ET of the natural shrubland by 100–200%. These increases in ET are only possible through the permanent use of groundwater either directly by the trees or through increased irrigation. This may significantly change the water balance in the area (e.g., high ET at the cost of a reduction in the water table), which renders large-scale plantations a questionable tool in sustainable arid-land management.}, number={8}, journal={JOURNAL OF ENVIRONMENTAL MANAGEMENT}, author={Wilske, Burkhard and Lu, Nan and Wei, Long and Chen, Shiping and Zha, Tonggang and Liu, Chenfeng and Xu, Wenting and Noormets, Asko and Huang, Jianhui and Wei, Yafen and et al.}, year={2009}, month={Jun}, pages={2762–2770} }
 @inbook{noormets_chen_gu_desai_2009, title={The phenology of gross ecosystem productivity and ecosystem respiration in temperate hardwood and conifer chronosequences}, DOI={10.1007/978-1-4419-0026-5_3}, booktitle={Phenology of ecosystem processes}, publisher={New York: Springer}, author={Noormets, A. and Chen, J. and Gu, L. and Desai, A.}, year={2009}, pages={59–85} }
 @article{ryu_chen_noormets_bresee_ollinger_2008, title={Comparisons between PnET-Day and eddy covariance based gross ecosystem production in two Northern Wisconsin forests}, volume={148}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2007.08.005}, abstractNote={Abstract The PnET-Day model was independently parameterized to compare with estimated eddy covariance gross ecosystem production (GEP; gC m −2  day −1 ) in a mature mixed hardwood and a mature red pine ( Pinus resinosa ) forest in Northern Wisconsin during the growing season of 2002 and 2003. The mature hardwood forest was dominated by Populus tremuloides , Populus grandidentata , Betula papyrifera , Quercus rubra , Acer rubrum , and Acer saccharum . We evaluated the model's capability to predict the seasonal and interannual dynamics of GEP and explored the sources of discrepancy between PnET-Day and eddy covariance GEP estimates. GEP was directly estimated from the two eddy-flux towers, one for each forest type, during 2002 and 2003. PnET-Day growing season GEP for the mature hardwood forest was 12% higher in 2002 and 12% lower in 2003 than eddy covariance GEP estimates, while the modeled growing season GEP of the mature red pine forest was overestimated by 43 and 32% compared to eddy covariance GEP in 2002 and 2003, respectively. The disagreement between the two methods was attributed to year-to-year variability in foliage biomass and foliar nitrogen (N) in the mature hardwood forest and to high foliage biomass and specific leaf weight in the mature red pine forest (>50% larger than red pine in Harvard Forest where the model was developed and validated). The difference between PnET-Day and eddy covariance GEP estimates was greatest in May in the hardwood forest, primarily due to the discrepancy between the true and parameterized foliage onset day. Our results suggest that improved prediction of foliage onset is necessary to improve PnET-Day estimation of GEP in a hardwood forest.}, number={2}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Ryu, Soung-Ryoul and Chen, Jiquan and Noormets, Asko and Bresee, Mary K. and Ollinger, Scott V.}, year={2008}, month={Feb}, pages={247–256} }
 @article{desai_richardson_moffat_kattge_hollinger_barr_falge_noormets_papale_reichstein_et al._2008, title={Cross-site evaluation of eddy covariance GPP and RE decomposition techniques}, volume={148}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2007.11.012}, abstractNote={Eddy covariance flux towers measure net exchange of land–atmosphere flux. For the flux of carbon dioxide, this net ecosystem exchange (NEE) is governed by two processes, gross primary production (GPP) and a sum of autotrophic and heterotrophic respiration components known as ecosystem respiration (RE). A number of statistical flux-partitioning methods, often developed to fill missing NEE data, can also be used to estimate GPP and RE from NEE time series. Here we present results of the first comprehensive, multi-site comparison of these partitioning methods. An initial test was performed with a subset of methods in retrieving GPP and RE from NEE generated by an ecosystem model, which was also degraded with realistic noise. All methods produced GPP and RE estimates that were highly correlated with the synthetic data at the daily and annual timescales, but most were biased low, including a parameter inversion of the original model. We then applied 23 different methods to 10 site years of temperate forest flux data, including 10 different artificial gap scenarios (10% removal of observations), in order to investigate the effects of partitioning method choice, data gaps, and intersite variability on estimated GPP and RE. Most methods differed by less than 10% in estimates of both GPP and RE. Gaps added an additional 6–7% variability, but did not result in additional bias. ANOVA showed that most methods were consistent in identifying differences in GPP and RE across sites, leading to increased confidence in previously published multi-site comparisons and syntheses. Several methods produced outliers at some sites, and some methods were systematically biased against the ensemble mean. Larger model spread was found for Mediterranean sites compared to temperate or boreal sites. For both real and synthetic data, high variability was found in modeling of the diurnal RE cycle, suggesting that additional study of diurnal RE mechanisms could help to improve partitioning algorithms.}, number={6-7}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Desai, Ankur R. and Richardson, Andrew D. and Moffat, Antje M. and Kattge, Jens and Hollinger, David Y. and Barr, Alan and Falge, Eva and Noormets, Asko and Papale, Dario and Reichstein, Markus and et al.}, year={2008}, month={Jun}, pages={821–838} }
 @article{noormets_mcnulty_deforest_sun_li_q._2008, title={Drought during canopy development has lasting effect on annual carbon balance in a deciduous temperate forest}, volume={179}, DOI={10.1111/j.1469-8137.2008.02501.x}, abstractNote={* Climate change projections predict an intensifying hydrologic cycle and an increasing frequency of droughts, yet quantitative understanding of the effects on ecosystem carbon exchange remains limited. * Here, the effect of contrasting precipitation and soil moisture dynamics were evaluated on forest carbon exchange using 2 yr of eddy covariance and microclimate data from a 50-yr-old mixed oak woodland in northern Ohio, USA. * The stand accumulated 40% less carbon in a year with drought between bud-break and full leaf expansion (354 +/- 81 g C m(-2) yr(-1) in 2004 and 252 +/- 45 g C m(-2) yr(-1) in 2005). This was caused by greater suppression of gross ecosystem productivity (GEP; 16% = 200 g) than of ecosystem respiration (ER; 11% = 100 g) by drought. Suppressed GEP was traced to lower leaf area, lower apparent quantum yield and lower canopy conductance. The moisture sensitivity of ER may have been mediated by GEP. * The results highlight the vulnerability of the ecosystem to even a moderate drought, when it affects a critical aspect of development. Although the drought was preceded by rain, the storage capacity of the soil seemed limited to 1-2 wk, and therefore droughts longer than this are likely to impair productivity in the region.}, number={3}, journal={New Phytologist}, author={Noormets, A. and McNulty, S. G. and DeForest, J. L. and Sun, G. and Li and Q., Chen}, year={2008}, pages={818–828} }
 @misc{xiao_zhuang_baldocchi_law_richardson_chen_oren_starr_noormets_ma_et al._2008, title={Estimation of net ecosystem carbon exchange for the conterminous United States by combining MODIS and AmeriFlux data}, volume={148}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2008.06.015}, abstractNote={Eddy covariance flux towers provide continuous measurements of net ecosystem carbon exchange (NEE) for a wide range of climate and biome types. However, these measurements only represent the carbon fluxes at the scale of the tower footprint. To quantify the net exchange of carbon dioxide between the terrestrial biosphere and the atmosphere for regions or continents, flux tower measurements need to be extrapolated to these large areas. Here we used remotely sensed data from the Moderate Resolution Imaging Spectrometer (MODIS) instrument on board the National Aeronautics and Space Administration's (NASA) Terra satellite to scale up AmeriFlux NEE measurements to the continental scale. We first combined MODIS and AmeriFlux data for representative U.S. ecosystems to develop a predictive NEE model using a modified regression tree approach. The predictive model was trained and validated using eddy flux NEE data over the periods 2000–2004 and 2005–2006, respectively. We found that the model predicted NEE well (r = 0.73, p < 0.001). We then applied the model to the continental scale and estimated NEE for each 1 km × 1 km cell across the conterminous U.S. for each 8-day interval in 2005 using spatially explicit MODIS data. The model generally captured the expected spatial and seasonal patterns of NEE as determined from measurements and the literature. Our study demonstrated that our empirical approach is effective for scaling up eddy flux NEE measurements to the continental scale and producing wall-to-wall NEE estimates across multiple biomes. Our estimates may provide an independent dataset from simulations with biogeochemical models and inverse modeling approaches for examining the spatiotemporal patterns of NEE and constraining terrestrial carbon budgets over large areas.}, number={11}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Xiao, Jingfeng and Zhuang, Qianlai and Baldocchi, Dennis D. and Law, Beverly E. and Richardson, Andrew D. and Chen, Jiquan and Oren, Ram and Starr, Gregory and Noormets, Asko and Ma, Siyan and et al.}, year={2008}, month={Oct}, pages={1827–1847} }
 @article{sun_noormets_chen_mcnulty_2008, title={Evapotranspiration estimates from eddy covariance towers and hydrologic modeling in managed forests in Northern Wisconsin, USA}, volume={148}, ISSN={["0168-1923"]}, DOI={10.1016/j.agrformet.2007.08.010}, abstractNote={Direct measurement of ecosystem evapotranspiration by the eddy covariance method and simulation modeling were employed to quantify the growing season (May–October) evapotranspiration (ET) of eight forest ecosystems representing a management gradient in dominant forest types and age classes in the Upper Great Lakes Region from 2002 to 2003. We measured net exchange of water vapor fluxes in a 63-year-old mature hardwood (MHW) stand, a 60-year-old mature red pine (MRP) stand, a 3-year-old young hardwood (YHW) stand, a 17-year-old intermediate hardwood (IHW) stand, a young red pine (YRP age 8) stand, an intermediate red pine (IRP age 21) stand, and two pine barren ecosystems burned 12 years (PB1) and 2 years (PB2) ago. Field data suggested that there were no significant differences in growing season (June–September) ET/precipitation ratio among all ecosystems in 2002. However, PB2 had significantly lower ET/precipitation than those of other ecosystems in 2003. The ratios were much higher for all ecosystems, up to 0.90 for IHW, during the peak summer months (June–July). PB2 was the lowest (0.64) during that period. Stand leaf area index alone did not explain ecosystem ET at the landscape scale. Seasonal ET values measured by the eddy covariance method were significantly lower than those simulated with a process-based hydrologic model, MIKE SHE. Our integration approach combined with field measurements and simulation modeling proved to be useful in providing a full picture of the effects of forest cover type change on landscape scale water balance at multiple temporal scales. The ET procedure used in the MIKE SHE model needs improvement to fully account for the effects of vapor pressure deficit on tree transpiration. Seasonal distributions of ET coincided with precipitation in the growing season, when fluxes estimated by both field and models were the highest. The simulation model suggests that removal of conifer forests in the study region may reduce ET immediately by 113–30 mm/year or about 20%, but our field data suggests that ET can recover within 8–25 years from re-growth of hardwood forests.}, number={2}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Sun, G. and Noormets, A. and Chen, J. and McNulty, S. G.}, year={2008}, month={Feb}, pages={257–267} }
 @article{desai_noormets_bolstad_chen_cook_davis_euskirchen_gough_martin_ricciuto_et al._2008, title={Influence of vegetation and seasonal forcing on carbon dioxide fluxes across the Upper Midwest, USA: Implications for regional scaling}, volume={148}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2007.08.001}, abstractNote={Carbon dioxide fluxes were examined over the growing seasons of 2002 and 2003 from 14 different sites in Upper Midwest (USA) to assess spatial variability of ecosystem–atmosphere CO2 exchange. These sites were exposed to similar temperature/precipitation regimes and spanned a range of vegetation types typical of the region (northern hardwood, mixed forest, red pine, jack pine, pine barrens and shrub wetland). The hardwood and red pine sites also spanned a range of stand ages (young, intermediate, mature). While seasonal changes in net ecosystem exchange (NEE) and photosynthetic parameters were coherent across the 2 years at most sites, changes in ecosystem respiration (ER) and gross ecosystem production (GEP) were not. Canopy height and vegetation type were important variables for explaining spatial variability of CO2 fluxes across the region. Light-use efficiency (LUE) was not as strongly correlated to GEP as maximum assimilation capacity (Amax). A bottom-up multi-tower land cover aggregated scaling of CO2 flux to a 2000 km2 regional flux estimate found June to August 2003 NEE, ER and GEP to be −290 ± 89, 408 ± 48, and 698 ± 73 gC m−2, respectively. Aggregated NEE, ER and GEP were 280% larger, 32% smaller and 3% larger, respectively, than that observed from a regionally integrating 447 m tall flux tower. However, when the tall tower fluxes were decomposed using a footprint-weighted influence function and then re-aggregated to a regional estimate, the resulting NEE, ER and GEP were within 11% of the multi-tower aggregation. Excluding wetland and young stand age sites from the aggregation worsened the comparison to observed fluxes. These results provide insight on the range of spatial sampling, replication, measurement error and land cover accuracy needed for multi-tiered bottom-up scaling of CO2 fluxes in heterogeneous regions such as the Upper Midwest, USA.}, number={2}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Desai, Ankur R. and Noormets, Asko and Bolstad, Paul V. and Chen, Jiquan and Cook, Bruce D. and Davis, Kenneth J. and Euskirchen, Eugenie S. and Gough, Christopher M. and Martin, Jonathan G. and Ricciuto, Daniel M. and et al.}, year={2008}, month={Feb}, pages={288–308} }
 @article{noormets_desai_cook_euskirchen_ricciuto_davis_bolstad_schmid_vogel_carey_et al._2008, title={Moisture sensitivity of ecosystem respiration: Comparison of 14 forest ecosystems in the Upper Great Lakes Region, USA}, volume={148}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2007.08.002}, abstractNote={Ecosystem respiration (ER) was measured with the eddy covariance technique in 14 forest ecosystems in the Upper Great Lakes Region during the growing seasons of 2002 and 2003. The response of ER to soil temperature and moisture was analyzed using empirical models. On average, ER was higher in the intermediate and young than in the mature stands, and higher in hardwood than in conifer stands. The seasonal mean temperature-normalized respiration rate (R10) ranged from 1 to 3 μmol CO2 m−2 s−1 and seasonal mean activation energy (Ea) from 40 to 110 kJ mol−1. The variation in the residuals of temperature response function of ER was best explained by soil moisture content. ER showed higher temperature sensitivity (as indicated by lower Ea) in the young than in the mature stands of coniferous forests, but not in the hardwood forests. The inclusion of soil moisture as an explicit driver of R10 explained an additional 8% (range 0–21%) of variability in ER. Significant moisture sensitivity of ER was detected in only 5 out of 20 site-years and it was associated with bimodal soil moisture distribution. Moisture sensitivity could partially be predicted from statistical moments kurtosis and interquartile range. The data implied greater moisture sensitivity with increasing stand age, possibly due to faster depletion of soil water supplies from a greater evaporative surface in the older stands. Additional limiting factors to ER were implicated.}, number={2}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Noormets, A. and Desai, A. R. and Cook, B. D. and Euskirchen, E. S. and Ricciuto, D. M. and Davis, K. J. and Bolstad, P. V. and Schmid, H. P. and Vogel, C. V. and Carey, E. V. and et al.}, year={2008}, month={Feb}, pages={216–230} }
 @article{oren_kull_noormets_2008, title={Olevi Kull's lifetime contribution to ecology}, volume={28}, ISSN={["1758-4469"]}, DOI={10.1093/treephys/28.4.483}, abstractNote={In this article dedicated to Olevi Kull (June 22, 1955-January 31, 2007), we draw on his writings (in English and translated) to outline his thoughts on the relationship between scientists and science. We provide a brief synthesis of his most important work, give a short account of his career and, to bring the man into focus, share some personal stories of interactions with him. Kull considered that for a personal understanding to become scientific knowledge it must be explained convincingly based on theory and empirical support, and then taught to others in both spoken and written words. He saw the last step as the main distinction between learning and science. Olevi Kull's approach to science relied on two principles: first, linking theory and experiments in challenging settings, e.g., to test the generality of his ideas he often challenged them in multi-layered, mixed-species canopies. Second, he insisted on setting experiments to test assumptions used in quantitative analyses or in explaining an observed outcome; this, at times, led to falsification of commonly held ideas, thus enhancing ecophysiological understanding. After describing Kull's application of these principles, we give a brief synthesis of his most important work, in which he demonstrated through experimentation and modeling how the vertical distribution of leaves in canopies is consistent with the acclimation of the photosynthetic apparatus. We also review some of his findings on the interactive effects of carbon dioxide and ozone on canopy photosynthesis.}, number={4}, journal={TREE PHYSIOLOGY}, author={Oren, Ram and Kull, Kalevi and Noormets, Asko}, year={2008}, month={Apr}, pages={483–490} }
 @article{john_chen_lu_guo_liang_wei_noormets_ma_han_2008, title={Predicting plant diversity based on remote sensing products in the semi-arid region of Inner Mongolia}, volume={112}, ISSN={["1879-0704"]}, DOI={10.1016/j.rse.2007.09.013}, abstractNote={Changes in species composition and diversity are the inevitable consequences of climate change, as well as land use and land cover change. Predicting species richness at regional spatial scales using remotely sensed biophysical variables has emerged as a viable mechanism for monitoring species distribution. In this study, we evaluate the utility of MODIS-based productivity (GPP and EVI) and surface water content (NDSVI and LSWI) in predicting species richness in the semi-arid region of Inner Mongolia, China. We found that these metrics correlated well with plant species richness and could be used in biome- and life form-specific models. The relationships were evaluated on the basis of county-level data recorded from the Flora of Inner Mongolia, stratified by administrative (i.e., counties), biome boundaries (desert, grassland, and forest), and grouped by life forms (trees, grasses, bulbs, annuals and shrubs). The predictor variables included: the annual, mean, maximum, seasonal midpoint (EVImid), standard deviation of MODIS-derived GPP, EVI, LSWI and NDSVI. The regional pattern of species richness correlated with GPPSD (R2 = 0.27), which was also the best predictor for bulbs, perennial herbs and shrubs (R2 = 0.36, 0.29 and 0.40, respectively). The predictive power of models improved when counties with > 50% of cropland were excluded from the analysis, where the seasonal dynamics of productivity and species richness deviate patterns in natural systems. When stratified by biome, GPPSD remained the best predictor of species richness in grasslands (R2 = 0.30), whereas the most variability was explained by NDSVImax in forests (R2 = 0.26), and LSWIavg in deserts (R2 = 0.61). The results demonstrated that biophysical estimates of productivity and water content can be used to predict plant species richness at the regional and biome levels.}, number={5}, journal={REMOTE SENSING OF ENVIRONMENT}, author={John, Ranjeet and Chen, Jiquan and Lu, Nan and Guo, Ke and Liang, Cunzhu and Wei, Yafen and Noormets, Asko and Ma, Keping and Han, Xingguo}, year={2008}, month={May}, pages={2018–2032} }
 @article{chen_bridgham_keller_pastor_noormets_weltzin_2008, title={Temperature Responses to Infrared-Loading and Water Table Manipulations in Peatland Mesocosms}, volume={50}, ISSN={["1672-9072"]}, DOI={10.1111/j.1744-7909.2008.00757.x}, abstractNote={Abstract}, number={11}, journal={JOURNAL OF INTEGRATIVE PLANT BIOLOGY}, author={Chen, Jiquan and Bridgham, Scott and Keller, Jason and Pastor, John and Noormets, Asko and Weltzin, Jake F.}, year={2008}, month={Nov}, pages={1484–1496} }
 @article{noormets_chen_crow_2007, title={Age-dependent changes in ecosystem carbon fluxes in managed forests in northern wisconsin, USA}, volume={10}, ISSN={["1435-0629"]}, DOI={10.1007/s10021-007-9018-y}, number={2}, journal={ECOSYSTEMS}, author={Noormets, Asko and Chen, Jiquan and Crow, Thomas R.}, year={2007}, month={Mar}, pages={187–203} }
 @article{moffat_papale_reichstein_hollinger_richardson_barr_beckstein_braswell_churkina_desai_et al._2007, title={Comprehensive comparison of gap-filling techniques for eddy covariance net carbon fluxes}, volume={147}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2007.08.011}, abstractNote={We review 15 techniques for estimating missing values of net ecosystem CO2 exchange (NEE) in eddy covariance time series and evaluate their performance for different artificial gap scenarios based on a set of 10 benchmark datasets from six forested sites in Europe. The goal of gap filling is the reproduction of the NEE time series and hence this present work focuses on estimating missing NEE values, not on editing or the removal of suspect values in these time series due to systematic errors in the measurements (e.g., nighttime flux, advection). The gap filling was examined by generating 50 secondary datasets with artificial gaps (ranging in length from single half-hours to 12 consecutive days) for each benchmark dataset and evaluating the performance with a variety of statistical metrics. The performance of the gap filling varied among sites and depended on the level of aggregation (native half-hourly time step versus daily), long gaps were more difficult to fill than short gaps, and differences among the techniques were more pronounced during the day than at night. The non-linear regression techniques (NLRs), the look-up table (LUT), marginal distribution sampling (MDS), and the semi-parametric model (SPM) generally showed good overall performance. The artificial neural network based techniques (ANNs) were generally, if only slightly, superior to the other techniques. The simple interpolation technique of mean diurnal variation (MDV) showed a moderate but consistent performance. Several sophisticated techniques, the dual unscented Kalman filter (UKF), the multiple imputation method (MIM), the terrestrial biosphere model (BETHY), but also one of the ANNs and one of the NLRs showed high biases which resulted in a low reliability of the annual sums, indicating that additional development might be needed. An uncertainty analysis comparing the estimated random error in the 10 benchmark datasets with the artificial gap residuals suggested that the techniques are already at or very close to the noise limit of the measurements. Based on the techniques and site data examined here, the effect of gap filling on the annual sums of NEE is modest, with most techniques falling within a range of ±25 g C m−2 year−1.}, number={3-4}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Moffat, Antje M. and Papale, Dario and Reichstein, Markus and Hollinger, David Y. and Richardson, Andrew D. and Barr, Alan G. and Beckstein, Clemens and Braswell, Bobby H. and Churkina, Galina and Desai, Ankur R. and et al.}, year={2007}, month={Dec}, pages={209–232} }
 @inbook{silbernagel_chen_noormets_song_2006, title={Conducting sound ecological studies at the landscape scale: hypotheses, experiments and challenges}, booktitle={Ecology of Hierarchical Landscapes: From Theory to Application}, publisher={Carbondale, IL: Nova Publishing}, author={Silbernagel, J. and Chen, J. and Noormets, A. and Song, B.}, editor={J. Chen, S. C. Saunders and K. D. Brosofske and Crow, T. R.Editors}, year={2006}, pages={283–297} }
 @article{deforest_noormets_mcnulty_sun_tenney_chen_2006, title={Phenophases alter the soil respiration-temperature relationship in an oak-dominated forest}, volume={51}, ISSN={["1432-1254"]}, DOI={10.1007/s00484-006-0046-7}, abstractNote={Soil respiration (SR) represents a major component of forest ecosystem respiration and is influenced seasonally by environmental factors such as temperature, soil moisture, root respiration, and litter fall. Changes in these environmental factors correspond with shifts in plant phenology. In this study, we examined the relationship between canopy phenophases (pre-growth, growth, pre-dormancy, and dormancy) and SR sensitivity to changes in soil temperature (T(S)). SR was measured 53 times over 550 days within an oak forest in northwest Ohio, USA. Annual estimates of SR were calculated with a Q(10) model based on T(S) on a phenological (PT), or annual timescale (AT), or T(S) and soil volumetric water content (VWC) on a phenological (PTM) or annual (ATM) timescale. We found significant (p<0.01) difference in apparent Q(10) from year 2004 (1.23) and year 2005 (2.76) during the growth phenophase. Accounting for moisture-sensitivity increased model performance compared to temperature-only models: the error was -17% for the ATM model and -6% for the PTM model. The annual models consistently underestimated SR in summer and overestimated it in winter. These biases were reduced by delineating SR by tree phenophases and accounting for variation in soil moisture. Even though the bias of annual models in winter SR was small in absolute scale, the relative error was about 91%, and may thus have significant implications for regional and continental C balance estimates.}, number={2}, journal={INTERNATIONAL JOURNAL OF BIOMETEOROLOGY}, author={DeForest, Jared L. and Noormets, Asko and McNulty, Steve G. and Sun, Ge and Tenney, Gwen and Chen, Jiquan}, year={2006}, month={Nov}, pages={135–144} }
 @inbook{noormets_ewers_sun_mackay_zheng_mcnulty_chen_2006, title={Water and carbon cycles in heterogeneous landscapes: an ecosystem perspective}, ISBN={1600210473}, booktitle={Ecology of Hierarchical Landscapes: From Theory to Application}, publisher={Carbondale, IL: Nova Publishing}, author={Noormets, A. and Ewers, B. and Sun, G. and Mackay, S. and Zheng, D. and McNulty, S. and Chen, J.}, editor={J. Chen, S. C. Saunders and K. D. Brosofske and Crow, T. R.Editors}, year={2006}, pages={89–123} }
 @article{zheng_chen_noormets_euskirchen_le moine_2005, title={Effects of climate and land use on landscape soil respiration in northern Wisconsin, USA: 1972 to 2001}, volume={28}, ISSN={["1616-1572"]}, DOI={10.3354/cr028163}, abstractNote={Changes in climate and land use affect soil respiration rates (SRR) significantly, but studies of these effects across entire landscapes are rare. We simulated responses of landscape mean SRR (LMSRR) to such changes from May to October over a 30 yr period in a managed, predominantly forested landscape in northern Wisconsin, USA, using: (1) 6 satellite-derived land-cover maps (1972, 1978, 1982, 1987, 1992, and 2001); (2) monthly air temperature data in the corresponding years of the cover maps; and (3) SRR models driven by soil temperature (Ts) at 5 cm depth. LMSRR seemed to increase linearly by 77% from 0.625 in May to 1.104 g CO2 m -2 h -1 in July, and then decreased at an increasing rate to 0.411 g CO2 m -2 h -1 in October. LMSRR was more sensitive to an increase of mini- mum temperature than that of mean or maximum temperature, suggesting that future climate change might impact SRR in high-latitude forests more than other biomes. LMSRR in September over the study period was similar to that of June but with 92% higher variation, while both landscape mean air temperature and precipitation in September had lower variation than in June. This indicates that the topsoil layer functions differently during soil warming and cooling phases. Changes in land cover composition from 1972 to 2001 increased LMSRR by 2.8 to 3.1% while 2°C differences in growing season mean air temperature increased the SRR by 6.7 to 7.0%. The combined effects of both vari- ables on the SRR are more complex, varying from 3.8 to 10.0%.}, number={2}, journal={CLIMATE RESEARCH}, author={Zheng, DL and Chen, JQ and Noormets, A and Euskirchen, ES and Le Moine, J}, year={2005}, month={Mar}, pages={163–173} }
 @article{chen_brosofske_noormets_crow_bresee_le moine_euskirchen_mather_zheng_2004, title={A working framework for quantifying carbon sequestration in disturbed land mosaics}, volume={33}, ISSN={["0364-152X"]}, DOI={10.1007/s00267-003-9131-4}, journal={ENVIRONMENTAL MANAGEMENT}, author={Chen, Jiquan and Brosofske, Kimberley D. and Noormets, Asko and Crow, Thomas R. and Bresee, Mary K. and Le Moine, James M. and Euskirchen, Eugenie S. and Mather, Steve V. and Zheng, Daolan}, year={2004}, month={Jul}, pages={S210–S221} }
 @misc{noormets_zhou_chen_2004, title={EC_Processor}, author={Noormets, A. and Zhou, R. and Chen, J.}, year={2004} }
 @article{noormets_chen_bridgham_weltzin_pastor_dewey_lemoine_2004, title={The effects of infrared loading and water table on soil energy fluxes in northern peatlands}, volume={7}, ISSN={["1435-0629"]}, DOI={10.1007/s10021-004-0013-2}, number={5}, journal={ECOSYSTEMS}, author={Noormets, A and Chen, JQ and Bridgham, SD and Weltzin, JF and Pastor, J and Dewey, B and LeMoine, J}, year={2004}, month={Aug}, pages={573–582} }
 @article{wustman_oksanen_karnosky_noormets_isebrands_pregitzer_hendrey_sober_podila_2003, title={Effects of elevated CO2 and O-3 on aspen clones of varying O-3 sensitivity}, volume={3}, ISBN={["0-08-044317-6"]}, ISSN={["1474-8177"]}, DOI={10.1016/s1474-8177(03)03022-5}, abstractNote={To determine whether elevated CO2 reduces or exacerbates the detrimental effects of O3 on aspen (Populus tremuloides Michx.). Aspen clones 216 and 271 (O3 tolerant), and 259 (O3 sensitive) were exposed to ambient levels of CO2 and O3 or elevated levels of CO2, O3, or CO2 + O3 in the FACTS II (Aspen FACE) experiment, and physiological and molecular responses were measured and compared. Clone 259, the most O3-sensitive clone, showed the greatest amount of visible foliar symptoms as well as significant decreases in chlorophyll, carotenoid, starch, and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) concentrations and transcription levels for the Rubisco small subunit. Generally, the constitutive (basic) transcript levels for phenylalanine ammonia-lyase (Pal) and chalcone synthase (Chs) and the average antioxidant activities were lower for the ozone sensitive clone 259 as compared to the more tolerant 216 and 271 clones. A significant decrease in chlorophyll a, b and total (a+b) concentrations in CO2, O3, and CO2 + O3 plants was observed for all clones. Carotenoid concentrations were also significantly lower in all clones; however, Chs transcript levels were not significantly affected, suggesting a possible degradation of carotenoid pigments in O3-stressed plants. Antioxidant activities and Pal and 1-aminocyclopropane-1-carboxylic acid (ACC)-oxidase transcript levels showed a general increase in all O3 treated clones, while remaining low in CO2 and CO2 + O3 plants (although not all differences were significant). Our results suggest that the ascorbate-glutathione and phenylpropanoid pathways were activated under ozone stress and suppressed during exposure to elevated CO2. Although CO2 + O3 treatment resulted in a slight reduction of O3-induced leaf injury, it did not appear to ameliorate all of the harmful affects of O3 and, in fact, may have contributed to an increase in chloroplast damage in all three aspen clones.}, journal={AIR POLLUTION, GLOBAL CHANGE AND FORESTS IN THE NEW MILLENNIUM}, author={Wustman, BA and Oksanen, E and Karnosky, DF and Noormets, A and Isebrands, JG and Pregitzer, KS and Hendrey, GR and Sober, J and Podila, GK}, year={2003}, pages={391–409} }
 @article{karnosky_percy_mankovska_prichard_noormets_dickson_jepsen_isebrands_2003, title={Ozone affects the fitness of trembling aspen}, volume={3}, ISBN={["0-08-044317-6"]}, ISSN={["1474-8177"]}, DOI={10.1016/s1474-8177(03)03008-0}, abstractNote={Abstract Trembling aspen ( Populus tremuloides Michx.) is sensitive to tropospheric ozone (O 3 ) as determined by visible foliar symptoms, accelerated foliar senescence and premature abscission, degradation and change in composition of epicuticular waxes, decreased photosynthesis and chlorophyll, and decreased aboveground and belowground growth. The species is highly variable in O 3 responses as some clones are similar in sensitivity to Bel W3 tobacco and other clones are tolerant to moderate levels of O 3 . We have, therefore, hypothesized and presented evidence for natural selection of O 3 -tolerance in aspen populations. This hypothesis has been criticized, however, as improbable because O 3 is thought to be a fairly weak selection force and because changes in tree population are thought to occur over very long time periods, longer than tropospheric O 3 has been known to be a problem. To shed more light on this argument, in 1994 we established a set of research field trials using clones of known origin and previously determined O 3 sensitivity at three sites in the Lake States region with differing O 3 profiles (Rhinelander, Wisconsin—low O 3 ; Kalamazoo, Michigan—moderate O 3 ; and Kenosha, Wisconsin—high O 3 ). In this paper, we present evidence of changes in the relative volume d 2 h growth of clone 259 (O 3 -sensitive) compared to clone 216 (O 3 -tolerant) of −0.1%, −44.2%, and −62.8% at the low, medium and high O 3 sites at age 5. In addition, relative survival of the clone 259 compared to 216 was −11.0%, −6.8%, and −38.4% at the low, moderate, and high O 3 sites. Actual survival rates at the high O 3 site were 78.2% for clone 216 and only 48.2% for clone 259. Our results suggest that very rapid and significant changes in competitive ability and fitness can occur under ambient levels of O 3 in the lower Great Lakes region for aggrading forests. These results are consistent with the hypothesis that O 3 is inducing natural selection for O 3 tolerance in aspen.}, journal={AIR POLLUTION, GLOBAL CHANGE AND FORESTS IN THE NEW MILLENNIUM}, author={Karnosky, DF and Percy, KE and Mankovska, B and Prichard, T and Noormets, A and Dickson, RE and Jepsen, E and Isebrands, JG}, year={2003}, pages={199–209} }
 @misc{karnosky_zak_pregitzer_awmack_bockheim_dickson_hendrey_host_king_kopper_et al._2003, title={Tropospheric O-3 moderates responses of temperate hardwood forests to elevated CO2: a synthesis of molecular to ecosystem results from the Aspen FACE project}, volume={17}, ISSN={["1365-2435"]}, DOI={10.1046/j.1365-2435.2003.00733.x}, abstractNote={Summary}, number={3}, journal={FUNCTIONAL ECOLOGY}, author={Karnosky, DF and Zak, DR and Pregitzer, KS and Awmack, CS and Bockheim, JG and Dickson, RE and Hendrey, GR and Host, GE and King, JS and Kopper, BJ and et al.}, year={2003}, month={Jun}, pages={289–304} }
 @article{karnosky_percy_xiang_callan_noormets_mankovska_hopkin_sober_jones_dickson_et al._2002, title={Interacting elevated CO2 and tropospheric O-3 predisposes aspen (Populus tremuloides Michx.) to infection by rust (Melampsora medusae f. sp tremuloidae)}, volume={8}, ISSN={["1365-2486"]}, DOI={10.1046/j.1354-1013.2002.00479.x}, abstractNote={Abstract}, number={4}, journal={GLOBAL CHANGE BIOLOGY}, author={Karnosky, DF and Percy, KE and Xiang, BX and Callan, B and Noormets, A and Mankovska, B and Hopkin, A and Sober, J and Jones, W and Dickson, RE and et al.}, year={2002}, month={Apr}, pages={329–338} }
 @article{wustman_oksanen_karnosky_noormets_isebrands_pregitzer_hendrey_sober_podila_2001, title={Effects of elevated CO2 and O-3 on aspen clones varying in O-3 sensitivity: can CO2 ameliorate the harmful effects of O-3?}, volume={115}, ISSN={["0269-7491"]}, DOI={10.1016/S0269-7491(01)00236-6}, abstractNote={To determine whether elevated CO2 reduces or exacerbates the detrimental effects of O3 on aspen (Populus tremuloides Michx.). aspen clones 216 and 271 (O3 tolerant), and 259 (O3 sensitive) were exposed to ambient levels of CO2 and O3 or elevated levels of CO2, O3, or CO2 + O3 in the FACTS II (Aspen FACE) experiment, and physiological and molecular responses were measured and compared. Clone 259. the most O3-sensitive clone, showed the greatest amount of visible foliar symptoms as well as significant decreases in chlorophyll, carotenoid, starch, and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) concentrations and transcription levels for the Rubisco small subunit. Generally, the constitutive (basic) transcript levels for phenylalanine ammonialyase (PAL) and chalcone synthase (CHS) and the average antioxidant activities were lower for the ozone sensitive clone 259 as compared to the more tolerant 216 and 271 clones. A significant decrease in chlorophyll a, b and total (a + b) concentrations in CO2, O3, and CO2 + O3 plants was observed for all clones. Carotenoid concentrations were also significantly lower in all clones; however. CHS transcript levels were not significantly affected, suggesting a possible degradation of carotenoid pigments in O3-stressed plants. Antioxidant activities and PAL and 1-aminocyclopropane-l-carboxylic acid (ACC)-oxidase transcript levels showed a general increase in all O3 treated clones, while remaining low in CO2 and CO2 + O3 plants (although not all differences were significant). Our results suggest that the ascorbate-glutathione and phenylpropanoid pathways were activated under ozone stress and suppressed during exposure to elevated CO2. Although CO2 + O2 treatment resulted in a slight reduction of O3-induced leaf injury, it did not appear to ameliorate all of the harmful affects of O3 and, in fact. may have contributed to an increase in chloroplast damage in all three aspen clones.}, number={3}, journal={ENVIRONMENTAL POLLUTION}, author={Wustman, BA and Oksanen, E and Karnosky, DF and Noormets, A and Isebrands, JG and Pregitzer, KS and Hendrey, GR and Sober, J and Podila, GK}, year={2001}, pages={473–481} }
 @article{noormets_sober_pell_dickson_podila_sober_isebrands_karnosky_2001, title={Stomatal and non-stomatal limitation to photosynthesis in two trembling aspen (Populus tremuloides Michx.) clones exposed to elevated CO2 and/or O-3}, volume={24}, ISSN={["1365-3040"]}, DOI={10.1046/j.1365-3040.2001.00678.x}, abstractNote={ABSTRACT}, number={3}, journal={PLANT CELL AND ENVIRONMENT}, author={Noormets, A and Sober, A and Pell, EJ and Dickson, RE and Podila, GK and Sober, J and Isebrands, JG and Karnosky, DF}, year={2001}, month={Mar}, pages={327–336} }
 @article{noormets_mcdonald_dickson_kruger_sober_isebrands_karnosky_2001, title={The effect of elevated carbon dioxide and ozone on leaf- and branch-level photosynthesis and potential plant-level carbon gain in aspen}, volume={15}, ISSN={["1432-2285"]}, DOI={10.1007/s004680100102}, number={5}, journal={TREES-STRUCTURE AND FUNCTION}, author={Noormets, A and McDonald, EP and Dickson, RE and Kruger, EL and Sober, A and Isebrands, JG and Karnosky, DF}, year={2001}, month={Jul}, pages={262–270} }
 @article{noormets_podila_karnosky_2000, title={Rapid response of antioxidant enzymes to O3-induced oxidative stress in Populus tremuloides clones varying in O3 tolerance}, volume={7}, journal={Forest Genetics}, author={Noormets, A. and Podila, G. K. and Karnosky, D. F.}, year={2000}, pages={339–342} }
 @article{karnosky_mankovska_percy_dickson_podila_sober_noormets_hendrey_coleman_kubiske_et al._1999, title={Effects of tropospheric O-3 on trembling aspen and interaction with CO2: Results from an O-3-gradient and a face experiment}, volume={116}, ISSN={["1573-2932"]}, DOI={10.1023/A:1005276824459}, number={1-2}, journal={WATER AIR AND SOIL POLLUTION}, author={Karnosky, DF and Mankovska, B and Percy, K and Dickson, RE and Podila, GK and Sober, J and Noormets, A and Hendrey, G and Coleman, MD and Kubiske, M and et al.}, year={1999}, month={Nov}, pages={311–322} }
 @inbook{karnosky_mankovska_percy_dickson_podila_sober_noormets_hendrey_coleman_kubiske_et al._1999, title={Effects of tropospheric O3 on trembling aspen and interaction with CO2: Results from an O3-gradient and a FACE experiment}, volume={116}, ISBN={0792359917}, DOI={10.1007/978-94-017-1578-2_24}, booktitle={Forest Growth Responses to the Pollution Climate of the 21st Century}, publisher={London: Kluwer Academic Publishers}, author={Karnosky, D. F. and Mankovska, B. and Percy, K. and Dickson, R. E. and Podila, G. K. and Sober, J. and Noormets, A. and Hendrey, G. and Coleman, M. D. and Kubiske, M. and et al.}, editor={L. J. Sheppard and Cape, J. N.Editors}, year={1999}, pages={311–322} }
 @article{akkapeddi_noormets_deo_karnosky_podila_1999, title={Gene structure and expression of the aspen cytosolic copper/zinc-superoxide dismutase (PtSodCc1)}, volume={143}, ISSN={["0168-9452"]}, DOI={10.1016/S0168-9452(99)00045-X}, abstractNote={Genomic and cDNA clones, corresponding to an ozone-induced cytosolic copper–zinc superoxide dismutase, were isolated from quaking aspen (Populus tremuloides Michx.). The cytosolic superoxide dismutase (SOD) appears to be part of a multi-gene family in aspen and is interrupted by five introns in the coding region. Northern blot analysis with a gene-specific probe revealed an increase in the expression of this gene in response to ozone in the leaves of an ozone-tolerant aspen clone, compared with an ozone-sensitive clone. Cytosolic SOD transcript expression levels in leaves were also found to increase significantly within 6 h of mechanical wounding, after which the level of the transcript decreases. Under normal growing conditions, immature male and female aspen floral bud tissues contained the highest levels of the cytosolic SOD gene transcript, whereas transcript levels were almost undetectable in older leaves.}, number={2}, journal={PLANT SCIENCE}, author={Akkapeddi, AS and Noormets, A and Deo, BK and Karnosky, DF and Podila, GK}, year={1999}, month={May}, pages={151–162} }
 @inproceedings{noormets_isebrands_podila_karnosky_1999, title={Stomatal versus mesophyll control of instantaneous photosynthesis in trembling aspen exposed to elevated CO2 and/or O3}, booktitle={Plant Biology '99: The Annual Meeting of the American Society of Plant Physiologists}, publisher={American Society of Plant Physiologists}, author={Noormets, A. and Isebrands, J. G. and Podila, G. K. and Karnosky, D. F.}, year={1999}, pages={119} }
 @inproceedings{noormets_karnosky_podila_1998, title={Antioxidant response of Populus tremuloides Michx. in early stages of oxidative stress}, booktitle={Plant Biology '98: The Annual Meeting of the American Society of Plant Physiologists}, publisher={American Society of Plant Physiologists}, author={Noormets, A. and Karnosky, D. F. and Podila, G. K.}, year={1998}, pages={91} }
 @article{kull_koppel_noormets_1998, title={Seasonal changes in leaf nitrogen pools in two Salix species}, volume={18}, DOI={10.1093/treephys/18.1.45}, abstractNote={Leaf nitrogen distribution pattern was studied four times during the growing season in a 2-year-old Salix viminalis L. and Salix dasyclados Wimm. plantation in Estonia. We measured the vertical distributions of leaf nitrogen concentration, dry mass, leaf area and light environment (as fractional transmission of diffuse irradiance, a(d)) in the canopy. The light-independent nitrogen pool was evaluated as the intercept of the leaf nitrogen concentration versus a(d) relationship, and the nondegradable nitrogen pool was evaluated as the nitrogen remaining in abscised leaves. A strong vertical gradient of mass-based leaf nitrogen concentration was detected at the beginning of the growing season, and decreased steadily during canopy development. This decline had at least three causes: (1) the amount of nitrogen in the foliage was larger at the beginning of the growing season than at the end of the growing season, probably because of pre-existing root systems; (2) with increasing leaf area index (LAI) during the growing season, the proportion of leaf nitrogen in total canopy nitrogen that could be redistributed (light-dependent nitrogen pool) decreased; and (3) the photosynthetic photon flux density gradient inside the canopy changed during the season, most probably because of changes in leaf area and leaf angle distributions. Total canopy nitrogen increased almost proportionally to LAI, whereas the light-dependent nitrogen pool had a maximum in August. Also, the proportion of the light-dependent nitrogen pool in the total canopy nitrogen decreased steadily from 65.2% in June to 17.2% in September in S. dasyclados and from 63.3 to 15.1% in S. viminalis. The degradable nitrogen pool was always bigger than the light-dependent nitrogen pool.}, journal={Tree Physiology}, author={Kull, O. and Koppel, A. and Noormets, A.}, year={1998}, pages={45–51} }
 @inproceedings{noormets_kull_koppel_1995, title={Nitrogen dynamics in Salix leaves during the first production year}, ISBN={9157651736}, booktitle={Short Rotation Willow Coppice for Renewable Energy and Improved Environment: Proceedings of a joint Swedish-Estonian seminar on Energy Forestry and Vegetation Filters}, publisher={Swedish University of Agricultural Sciences, Uppsala}, author={Noormets, A. and Kull, O. and Koppel, A.}, editor={K. Perttu and Koppel, A.Editors}, year={1995}, pages={51–60} }