@article{heckman_khasanova_johnson_weber_bonnette_aspinwall_reichmann_juenger_fay_hawkes_2020, title={Plant biomass, not plant economics traits, determines responses of soil CO2 efflux to precipitation in the C-4 grass Panicum virgatum}, volume={108}, ISSN={["1365-2745"]}, DOI={10.1111/1365-2745.13382}, abstractNote={Abstract Plant responses to major environmental drivers like precipitation can influence important aspects of carbon (C) cycling like soil CO 2 efflux ( ). These responses may be predicted by two independent classes of drivers: plant size—larger plants respire more and produce a larger quantity of labile C, and plant economics—plants possessing more acquisitive plant economics strategies (i.e. high metabolic rate and tissue nutrient content) produce higher‐quality tissue that respires rapidly and decomposes quickly. At two sites in central Texas, USA with similar climates and differing soil characteristics, we examined the response of eight Panicum virgatum genotypes to three annual precipitation levels defined by the driest, average and wettest years from each site's precipitation history. We evaluated the individual and joint influence of plant genotypes and precipitation on and traits related to plant economics and plant size. We then used confirmatory path analysis to evaluate whether effects of precipitation on were in part related to effects of precipitation on plant economics traits or size (‘mediated’ effects). These genotypes exhibited variation in plant economics traits and above‐ground net primary productivity (ANPP), an above‐ground measure of plant size. Increasing precipitation increased and ANPP more than plant economics traits. At both sites, ANPP was the best predictor of . Moreover, the sites differed in the ways that plant size and plant economics traits combined with precipitation to influence . At the Austin site, the positive effect of precipitation on was mediated primarily by ANPP, offset by a smaller effect of leaf nitrogen content; no direct precipitation effect was detected. At the Temple site, increasing precipitation had positive direct and ANPP‐mediated effects on . This suggests that greater water limitation at Austin may strengthen the links between plant size and . Synthesis . Estimates of C cycling can be improved by accounting for mediation of precipitation effects on by plant economics traits and plant size in resource‐limited environments.}, number={5}, journal={JOURNAL OF ECOLOGY}, author={Heckman, Robert W. and Khasanova, Albina R. and Johnson, Nicholas S. and Weber, Soren and Bonnette, Jason E. and Aspinwall, Michael J. and Reichmann, Lara G. and Juenger, Thomas E. and Fay, Philip A. and Hawkes, Christine V}, year={2020}, month={Sep}, pages={2095–2106} }
 @article{aspinwall_king_mckeand_2013, title={Productivity differences among loblolly pine genotypes are independent of individual-tree biomass partitioning and growth efficiency}, volume={27}, ISSN={["1432-2285"]}, DOI={10.1007/s00468-012-0806-4}, number={3}, journal={TREES-STRUCTURE AND FUNCTION}, author={Aspinwall, Michael J. and King, John S. and McKeand, Steven E.}, year={2013}, month={Jun}, pages={533–545} }
 @article{aspinwall_mckeand_king_2012, title={Carbon Sequestration from 40 Years of Planting Genetically Improved Loblolly Pine across the Southeast United States}, volume={58}, ISSN={["1938-3738"]}, DOI={10.5849/forsci.11-058}, abstractNote={Highly productive, widely deployed genetically improved loblolly pine (Pinus taeda L.) may play an important role in mitigating rising atmospheric CO2 via carbon (C) sequestration. To understand the role of loblolly pine genetic improvement in future C sequestration strategies, we examined the historical (1968–2007) impact of operationally deploying improved families of loblolly pine on productivity and C sequestration across the southeast United States. Since 1977, nearly 100% of loblolly pine plantations in the southeast United States have been established with genetically improved loblolly pine. In recent years, more than 400,000 ha of genetically improved loblolly pine are planted annually. Between 1968 and 2007, we estimate that genetically improved loblolly pine plantations have produced a total of 25.6 billion m3 of stemwood volume and have sequestered 9,865 Tg C in live and dead biomass. Our estimates also indicate that genetic improvement has resulted in an additional 3.7 billion m3 (17% increase) and 1,100 Tg C (13%) of volume production and C sequestration, respectively, relative to volume production and C sequestration with no genetic improvement. We expect that loblolly pine plantation C sequestration will increase as more productive families and clones are deployed and as currently deployed genetic material continues to mature. Together, genetic improvement, intensive silvicultural, and longer rotations aimed at producing long-lived wood products will be important tools for maximizing C sequestration in loblolly pine plantations.}, number={5}, journal={FOREST SCIENCE}, author={Aspinwall, Michael J. and McKeand, Steven E. and King, John S.}, year={2012}, month={Oct}, pages={446–456} }
 @article{aspinwall_king_mckeand_bullock_2011, title={Genetic effects on stand-level uniformity and above- and belowground dry mass production in juvenile loblolly pine}, volume={262}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2011.04.029}, abstractNote={Genetic differences in stand-level above- and belowground dry mass production in loblolly pine (Pinus taeda L.) may influence southern pine plantation productivity, sustainability and carbon (C) sequestration. Furthermore, deployment of more or less genetically homogeneous individuals could impact stand uniformity and ecosystem processes. In this study, we aimed to compare stand uniformity and above- and belowground dry mass production among loblolly pine genotypes of contrasting inherent genetic homogeneity. We hypothesized that stand-level uniformity would increase as within-genotype inherent genetic variation decreased (open-pollinated (half-sib) > full-sib > clone). To examine genetic effects on stand uniformity and productivity, we grew ten different genotypes (three open-pollinated families, three full-sib families, three clones, and one seed orchard mix variety) in a plantation setting for 4 years, at two different planting densities (∼539 and 1077 trees ha−1), and used allometric relationships to estimate standing dry mass and annual dry mass production. In the low planting density treatment, age 3 total standing dry mass of the most productive genotype (5824 kg ha−1) was 82% higher than that of the least productive genotype (3207 kg ha−1). In the high planting density treatment, age 3 total standing dry mass of the most productive genotype (11,393 kg ha−1) was 110% higher than that of the least productive genotype (5427 kg ha−1). Genetic differences in annual dry mass production were of a similar magnitude with peak rates during the third year as high as 4221 and 8198 kg ha−1 yr−1 in the low and high planting density treatments, respectively. More genetically homogeneous genotypes did not show greater stand-level uniformity under operational management conditions. Over time, genotypes showed no consistent differences in the coefficient of variation (CV) for ground-level diameter; however, two full-sib and two half-sib families showed significantly lower CV’s for total tree height than all three clones. Moreover, genotypes with lower CV’s for height growth displayed greater stand-level dry mass production which supports the premise that greater stand uniformity will lead to enhanced productivity. Since uniformity and stand-level productivity of loblolly pine clones will be principally governed by environmental heterogeneity, our results highlight the need for silvicultural prescriptions that maximize site uniformity. In addition, our results demonstrate how the deployment of highly productive loblolly pine genotypes may provide a means of enhancing southern pine ecosystem sustainability by sequestering C in both harvestable aboveground biomass and woody belowground biomass.}, number={4}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Aspinwall, Michael J. and King, John S. and McKeand, Steven E. and Bullock, Bronson P.}, year={2011}, month={Aug}, pages={609–619} }
 @article{aspinwall_king_booker_mckeand_2011, title={Genetic effects on total phenolics, condensed tannins and non-structural carbohydrates in loblolly pine (Pinus taeda L.) needles}, volume={31}, ISSN={["1758-4469"]}, DOI={10.1093/treephys/tpr073}, abstractNote={Carbon allocation to soluble phenolics (total phenolics, proanthocyanidins (PA)) and total non-structural carbohydrates (TNC; starch and soluble sugars) in needles of widely planted, highly productive loblolly pine (Pinus taeda L.) genotypes could impact stand resistance to herbivory, and biogeochemical cycling in the southeastern USA. However, genetic and growth-related effects on loblolly pine needle chemistry are not well characterized. Therefore, we investigated genetic and growth-related effects on foliar concentrations of total phenolics, PA and TNC in two different field studies. The first study contained nine different genotypes representing a range of genetic homogeneity, growing in a 2-year-old plantation on the coastal plain of North Carolina (NC), USA. The second study contained eight clones with different growth potentials planted in a 9-year-old clonal trial replicated at two sites (Georgia (GA) and South Carolina (SC), USA). In the first study (NC), we found no genetic effects on total phenolics, PA and TNC, and there was no relationship between genotype size and foliar biochemistry. In the second study, there were no differences in height growth between sites, but the SC site showed greater diameter (diameter at breast height (DBH)) and volume, most likely due to greater tree mortality (lower stocking) which reduced competition for resources and increased growth of remaining trees. We found a significant site × clone effect for total phenolics with lower productivity clones showing 27–30% higher total phenolic concentrations at the GA site where DBH and volume were lower. In contrast to the predictions of growth–defense theory, clone volume was positively associated with total phenolic concentrations at the higher volume SC site, and PA concentrations at the lower volume GA site. Overall, we found no evidence of a trade-off between genotype size and defense, and genetic potential for improved growth may include increased allocation to some secondary metabolites. These results imply that deployment of more productive loblolly pine genotypes will not reduce stand resistance to herbivory, but increased production of total phenolics and PA associated with higher genotype growth potential could reduce litter decomposition rates and therefore, nutrient availability.}, number={8}, journal={TREE PHYSIOLOGY}, author={Aspinwall, Michael J. and King, John S. and Booker, Fitzgerald L. and McKeand, Steven E.}, year={2011}, month={Aug}, pages={831–842} }
 @article{aspinwall_king_domec_mckeand_isik_2011, title={Genetic effects on transpiration, canopy conductance, stomatal sensitivity to vapour pressure deficit, and cavitation resistance in loblolly pine}, volume={4}, ISSN={1936-0584}, url={http://dx.doi.org/10.1002/eco.197}, DOI={10.1002/eco.197}, abstractNote={Abstract Physiological uniformity and genetic effects on canopy‐level gas‐exchange and hydraulic function could impact loblolly pine ( Pinus taeda L.) plantation sustainability and ecosystem dynamics under projected changes in climate. Over a 1‐year period, we examined genetic effects on mean and maximum mid‐day canopy conductance ( G s , G smax ) and transpiration ( E , max‐ E ) within a juvenile loblolly pine plantation composed of ‘genotypes’ (e.g. different genetic entries) from each of the three different genetic groups (clones, full‐sibs, open‐pollinated). We also compared reference canopy conductance ( G s−ref or G s at a vapour pressure deficit ( D ) = 1 kPa), maximum E ( E max ) in response to D , stomatal sensitivity to D , specific hydraulic conductivity ( k s ), and cavitation resistance among genotypes. Based on genetic and physiological principles, we hypothesized that (1) within genotypes, physiological uniformity will increase as inherent genetic diversity decreases and (2) genotypes with greater k s and higher canopy‐level gas‐exchange rates will be more sensitive to increases in D , and more susceptible to loss of k s . In our results, high‐ and low‐genetic diversity genotypes showed no differences in E and G s uniformity over time. However, E and max‐ E were significantly different among genotypes, and genotypes showed significant seasonal variability in G s and G smax . Additionally, there were significant differences in E max , G s−ref , G s sensitivity to D , and the pressure at which 50% loss of k s occurs ( P 50 ) among individual genotypes. We found no relationship between mean hydraulic conductivity parameters and overall G s−ref or G s sensitivity. However, the genotype full embolism point ( P 88 ) and loss of k s rate (LC rate ) both showed a significant positive relationship with genotype G s−ref during the spring, indicating that genotypes with higher G s were less resistant to cavitation. Overall, genetic effects on canopy‐level gas‐exchange and cavitation resistance were significant, implying that physiological differences among genotypes might affect stand water use, carbon gain, drought tolerance, and hydrologic processes. Contrary to our expectations, uniformity in physiological process rates did not increase as inherent genetic diversity decreased, suggesting that clonal genotypes exhibit high physiological plasticity under plantation conditions. Lastly, our results imply that genotypes with higher spring‐time gas‐exchange rates may be more susceptible to catastrophic loss of k s . With changes in climate expected to continue, physiological differences among genotypes may affect loblolly pine plantation carbon and water cycling. Copyright © 2011 John Wiley & Sons, Ltd.}, number={2}, journal={Ecohydrology}, publisher={Wiley}, author={Aspinwall, Michael J. and King, John S. and Domec, Jean-Christophe and McKeand, Steven E. and Isik, Fikret}, year={2011}, month={Jan}, pages={168–182} }
 @article{aspinwall_king_mckeand_domec_2011, title={Leaf-level gas-exchange uniformity and photosynthetic capacity among loblolly pine (Pinus taeda L.) genotypes of contrasting inherent genetic variation}, volume={31}, ISSN={["1758-4469"]}, DOI={10.1093/treephys/tpq107}, abstractNote={Variation in leaf-level gas exchange among widely planted genetically improved loblolly pine (Pinus taeda L.) genotypes could impact stand-level water use, carbon assimilation, biomass production, C allocation, ecosystem sustainability and biogeochemical cycling under changing environmental conditions. We examined uniformity in leaf-level light-saturated photosynthesis (Asat), stomatal conductance (gs), and intrinsic water-use efficiency (Asat/gs or δ) among nine loblolly pine genotypes (selected individuals): three clones, three full-sib families and three half-sib families, during the early years of stand development (first 3 years), with each genetic group possessing varying amounts of inherent genetic variation. We also compared light- and CO2-response parameters between genotypes and examined the relationship between genotype productivity, gas exchange and photosynthetic capacity. Within full-sib, half-sib and clonal genotypes, the coefficient of variation (CV) for gas exchange showed no consistent pattern; the CV for gs and δ was similar within clonal (44.3–46.9 and 35.5–38.6%) and half-sib (41.0–49.3 and 36.8–40.9%) genotypes, while full-sibs showed somewhat higher CVs (46.9–56.0 and 40.1–45.4%). In contrast, the CVs for Asat were generally higher within clones. With the exception of δ, differences in gas exchange among genotypes were generally insignificant. Tree volume showed a significant positive correlation with Asat and δ, but the relationship varied by season. Individual-tree volume and genotype volume were positively correlated with needle dark respiration (Rd). Our results suggest that uniformity in leaf-level physiological rates is not consistently related to the amount of genetic variation within a given genotype, and δ, Asat and Rd were the leaf-level physiological parameters that were most consistently related to individual-tree and genotype productivity. An enhanced understanding of molecular and environmental factors that influence physiological variation within and between loblolly pine genotypes may improve assessments of genotype growth potential and sensitivity to global climate change.}, number={1}, journal={TREE PHYSIOLOGY}, author={Aspinwall, Michael J. and King, John S. and McKeand, Steven E. and Domec, Jean-Christophe}, year={2011}, month={Jan}, pages={78–91} }
 @article{aspinwall_li_mckeand_isik_gumpertz_2010, title={Prediction of whole-stem alpha-cellulose yield, lignin content, and wood density in juvenile and mature loblolly pine}, volume={34}, number={2}, journal={Southern Journal of Applied Forestry}, author={Aspinwall, M. J. and Li, B. L. and McKeand, S. E. and Isik, F. and Gumpertz, M. L.}, year={2010}, pages={84–90} }