@article{minick_aguilos_li_mitra_prajapati_king_2022, title={Effects of Spatial Variability and Drainage on Extracellular Enzyme Activity in Coastal Freshwater Forested Wetlands of Eastern North Carolina, USA}, volume={13}, ISSN={1999-4907}, url={http://dx.doi.org/10.3390/f13060861}, DOI={10.3390/f13060861}, abstractNote={Drainage of freshwater wetlands is common in coastal regions, although the effects on microbial extracellular enzyme activity (a key mediator of soil organic matter decomposition) in relation to spatial variability (microtopography and soil depth) are poorly understood. Soils were collected from organic (Oi, Oe, Oa) and mineral (A, AB, B) horizons from a natural and drained coastal forested wetland in North Carolina, USA. Activity of seven enzymes were measured: α-glucosidase (AG), β-glucosidase (BG), cellobiohydrolase (CBH), xylosidase (XYL), phenol oxidase (POX), peroxidase (PER) and N-acetyl glucosamide (NAG). Enzyme activity rates were normalized by soil weight, soil organic C (SOC), and microbial biomass C (MBC). Specific enzyme activity (per SOC or MBC) was more sensitive to drainage and soil depth compared to normalization by soil weight. In Oi and Oa horizons, specific enzyme activity (per MBC) (AG, BG, XYL, POX, PER) was higher in the natural compared to drained wetland but lower (AG, CBH, XYL, POX, PER, NAG) in the AB or B mineral soils. Results from this study indicate that organic soil horizons of natural freshwater wetlands contain a highly active microbial community driven by inputs of plant-derived C, while deeper soils of the drained wetland exhibit higher microbial metabolic activity, which likely plays a role in SOC storage of these systems.}, number={6}, journal={Forests}, publisher={MDPI AG}, author={Minick, Kevan J. and Aguilos, Maricar and Li, Xuefeng and Mitra, Bhaskar and Prajapati, Prajaya and King, John S.}, year={2022}, month={May}, pages={861} }
 @article{li_zheng_zhou_mcnulty_king_2022, title={Measurements of fine root decomposition rate: Method matters}, volume={164}, ISSN={["1879-3428"]}, DOI={10.1016/j.soilbio.2021.108482}, abstractNote={Fine root decomposition plays a major role in biogeochemical cycle in forests. Litterbags and intact cores are predominant methods for measuring fine root decomposition rate. However, their efficacies have not been critically reviewed. In this study, we identify six sources of error for both methods including use of unrepresentative substrates, changes in decomposer community composition, altered effects of living roots and mycorrhizal fungi, differences in experimental duration length and sampling regime, confounding of spatiotemporal resolution, and limited temporal resolution. We present an indirect method to quantify fine root decomposition rate by integrating soil core and minirhizotron measurements into a new equation. The indirect method requires measuring more fine root parameters but can generally overcome the weaknesses associated with litterbag and intact core methods. Directly measuring the decomposition rate inevitably disturbs interactions between roots, soil fauna and rhizosphere microbes, which could significantly undermine the credibility of the estimates. Indirect measurement based on fine root growth and death rates, biomass and necromass that can be assessed reliably should be the future choice.}, journal={SOIL BIOLOGY & BIOCHEMISTRY}, author={Li, Xuefeng and Zheng, Xingbo and Zhou, Quanlai and McNulty, Steven and King, John S.}, year={2022}, month={Jan} }
 @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_li_williamson_gavazzi_mcnulty_king_2020, title={An improved method for quantifying total fine root decomposition in plantation forests combining measurements of soil coring and minirhizotrons with a mass balance model}, volume={40}, ISSN={["1758-4469"]}, DOI={10.1093/treephys/tpaa074}, abstractNote={Abstract}, number={10}, journal={TREE PHYSIOLOGY}, author={Li, Xuefeng and Minick, Kevan J. and Li, Tonghua and Williamson, James C. and Gavazzi, Michael and McNulty, Steven and King, John S.}, year={2020}, month={Oct}, pages={1466–1473} }
 @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{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_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{li_king_2018, title={An improved method for measuring the production, mortality and decomposition of extramatrical mycelia of ectomycorrhizal fungi in forests}, volume={116}, ISSN={0038-0717}, url={http://dx.doi.org/10.1016/J.SOILBIO.2017.10.035}, DOI={10.1016/j.soilbio.2017.10.035}, abstractNote={Abstract The production and mortality of extramatrical mycelia (EMM) of ectomycorrhizal fungi are poorly quantified despite their importance in soil carbon cycling in forests. Ingrowth bag/core methods are the most widely used but can not accurately assess temporal changes in EMM production and mortality, resulting in great uncertainty in annual estimates. A modified method using two mathematical models (Biomarker and Algebraic models) is proposed to quantify EMM production, mortality and decomposition over differing time periods by integrating EMM decomposition dynamics with ingrowth core/bag data. In the Biomarker model, EMM biomass and EMM total mass (sum of necromass and biomass) are assumed to be known by using chemical biomarkers as proxies. In the Algebraic model, only the total mass is known and the biomass is calculated using an algebraic method. Model application in a loblolly pine plantation showed that mean monthly EMM production, mortality and decomposition estimates among three time periods ranged from 10.1 to 16.0 kg ha−1, 6.6–15.0 kg ha−1, and 1.4–6.1 kg ha−1, respectively, when using the Biomarker model, while these estimates ranged from 24.8 to 35.7 kg ha−1, 15.5–22.8 kg ha−1, and 5.7–9.8 kg ha−1, respectively, when using the Algebraic model, demonstrating the importance of assessing temporal changes. Model validation indicated that EMM estimates were more reliable for short-term compared to long-term incubation (184 vs. 322 days). Our method could improve EMM estimation by accurately assessing temporal changes in EMM production, mortality and decomposition in forests.}, journal={Soil Biology and Biochemistry}, publisher={Elsevier BV}, author={Li, Xuefeng and King, John S.}, year={2018}, month={Jan}, pages={360–368} }
 @article{hirao_watanabe_tsuyuzaki_shimono_li_masuzawa_wada_2017, title={Genetic diversity within populations of an arctic-alpine species declines with decreasing latitude across the Northern Hemisphere}, volume={44}, ISSN={["1365-2699"]}, DOI={10.1111/jbi.13085}, abstractNote={Abstract}, number={12}, journal={JOURNAL OF BIOGEOGRAPHY}, author={Hirao, Akira S. and Watanabe, Mikio and Tsuyuzaki, Shiro and Shimono, Ayako and Li, Xuefeng and Masuzawa, Takehiro and Wada, Naoya}, year={2017}, month={Dec}, pages={2740–2751} }
 @article{li_lange_2015, title={A modified soil coring method for measuring fine root production, mortality and decomposition in forests}, volume={91}, ISSN={["0038-0717"]}, DOI={10.1016/j.soilbio.2015.08.015}, abstractNote={Fine root (diameter < 2 mm) production, mortality and decomposition have been poorly estimated at ecosystem scales due to technical limitations. The soil coring method can accurately assess fine root biomass and necromass, but the concurrent growth, death and decomposition processes were not reasonably assessed during the sampling period, leading to greatly biased rate estimates. We developed a dynamic-flow method with two variations to address these processes by combining the soil coring method with an improved decomposition experiment. For a certain interval i (1 ≤ i) in the growing season, the dead fine roots were classified into fine roots dying before the start of interval i (GⅠ-i) and those dying during interval i (GⅡ-i). The decompositions of GⅠ-i and GⅡ-i were separately quantified and integrated into a modified mass balance model to estimate the production, mortality and decomposition. An example study conducted in a secondary Mongolian oak (Quercus mongolica Fischer ex Ledebour) forest showed that fine root production, mortality and decomposition were greatly underestimated by conventional soil coring methods failing to address the simultaneous growth, death and decomposition processes but overestimated by the method in which the decompositions of GⅠ-i and GⅡ-i were not separately determined and the decomposition rate was assumed to be constant. The dynamic-flow method greatly improved the accuracy of fine root estimates and can be widely applied to forests.}, journal={SOIL BIOLOGY & BIOCHEMISTRY}, author={Li, Xuefeng and Lange, Holger}, year={2015}, month={Dec}, pages={192–199} }