@article{marchin_stout_davis_king_2017, title={Transgenically altered lignin biosynthesis affects photosynthesis and water relations of field-grown Populus trichocarpa}, volume={98}, ISSN={["1873-2909"]}, DOI={10.1016/j.biombioe.2017.01.013}, abstractNote={Concerns over energy security and environmental sustainability have stimulated interest in development of high-yield, low-lignin trees for bioenergy. Black cottonwood (Populus trichocarpa) has been targeted as a potential bioenergy species due to its high productivity, but it is unclear how transgenically altered lignin biosynthesis will affect plant function. We investigated the physiology of two transgenic P. trichocarpa genotypes grown in short rotation woody cropping systems at two sites in southeastern USA: (1) mesic mountain site and (2) warmer, drier Piedmont site. Our results suggest that lignin is fundamental for tree growth and survival in field environments. Lignin deficiency can decrease biochemical photosynthetic processes and interfere with the temperature-response of photosynthesis. Significantly, hydraulic conductivity of transgenic genotypes was 15–25% that of wildtype trees, resulting in decreased leaf-specific whole-plant hydraulic conductance. In the Piedmont, decreased hydraulic efficiency drastically reduced productivity of low-lignin genotypes by 50–70% relative to wildtype. Transgenic trees at the mountain site recovered stem lignin concentrations to levels observed in wildtype trees, but still had severely impaired hydraulic traits, highlighting the major consequences of genetic transformation on whole-plant function. Surprisingly, substantial loss of hydraulic conductivity had only minor effects on productivity at the mesic site and resulted in an alternative advantage for bioenergy systems – lower water consumption. In the hottest month (July), higher intrinsic water use efficiency resulted in total water savings of roughly 1 kg d−1 per transgenic tree without sacrificing productivity. Decreased hydraulic conductivity could therefore be a promising trait for selection of water-efficient genotypes in Populus.}, journal={BIOMASS & BIOENERGY}, author={Marchin, Renee M. and Stout, Anna T. and Davis, Aletta A. and King, John S.}, year={2017}, month={Mar}, pages={15–25} }
 @article{marchin_broadhead_bostic_dunn_hoffmann_2016, title={Stomatal acclimation to vapour pressure deficit doubles transpiration of small tree seedlings with warming}, volume={39}, ISSN={0140-7791}, url={http://dx.doi.org/10.1111/pce.12790}, DOI={10.1111/pce.12790}, abstractNote={AbstractFuture climate change is expected to increase temperature (T) and atmospheric vapour pressure deficit (VPD) in many regions, but the effect of persistent warming on plant stomatal behaviour is highly uncertain. We investigated the effect of experimental warming of 1.9–5.1 °C and increased VPD of 0.5–1.3 kPa on transpiration and stomatal conductance (gs) of tree seedlings in the temperate forest understory (Duke Forest, North Carolina, USA). We observed peaked responses of transpiration to VPD in all seedlings, and the optimum VPD for transpiration (Dopt) shifted proportionally with increasing chamber VPD. Warming increased mean water use of Carya by 140% and Quercus by 150%, but had no significant effect on water use of Acer. Increased water use of ring‐porous species was attributed to (1) higher air T and (2) stomatal acclimation to VPD resulting in higher gs and more sensitive stomata, and thereby less efficient water use. Stomatal acclimation maintained homeostasis of leaf T and carbon gain despite increased VPD, revealing that short‐term stomatal responses to VPD may not be representative of long‐term exposure. Acclimation responses differ from expectations of decreasing gs with increasing VPD and may necessitate revision of current models based on this assumption.}, number={10}, journal={Plant, Cell & Environment}, publisher={Wiley}, author={Marchin, Renée M. and Broadhead, Alice A. and Bostic, Laura E. and Dunn, Robert R. and Hoffmann, William A.}, year={2016}, month={Aug}, pages={2221–2234} }
 @article{marchin_salk_hoffmann_dunn_2015, title={Temperature alone does not explain phenological variation of diverse temperate plants under experimental warming}, volume={21}, ISSN={["1365-2486"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84937524423&partnerID=MN8TOARS}, DOI={10.1111/gcb.12919}, abstractNote={AbstractAnthropogenic climate change has altered temperate forest phenology, but how these trends will play out in the future is controversial. We measured the effect of experimental warming of 0.6–5.0 °C on the phenology of a diverse suite of 11 plant species in the deciduous forest understory (Duke Forest, North Carolina, USA) in a relatively warm year (2011) and a colder year (2013). Our primary goal was to dissect how temperature affects timing of spring budburst, flowering, and autumn leaf coloring for functional groups with different growth habits, phenological niches, and xylem anatomy. Warming advanced budburst of six deciduous woody species by 5–15 days and delayed leaf coloring by 18–21 days, resulting in an extension of the growing season by as much as 20–29 days. Spring temperature accumulation was strongly correlated with budburst date, but temperature alone cannot explain the diverse budburst responses observed among plant functional types. Ring‐porous trees showed a consistent temperature response pattern across years, suggesting these species are sensitive to photoperiod. Conversely, diffuse‐porous species responded differently between years, suggesting winter chilling may be more important in regulating budburst. Budburst of the ring‐porous Quercus alba responded nonlinearly to warming, suggesting evolutionary constraints may limit changes in phenology, and therefore productivity, in the future. Warming caused a divergence in flowering times among species in the forest community, resulting in a longer flowering season by 10‐16 days. Temperature was a good predictor of flowering for only four of the seven species studied here. Observations of interannual temperature variability overpredicted flowering responses in spring‐blooming species, relative to our warming experiment, and did not consistently predict even the direction of flowering shifts. Experiments that push temperatures beyond historic variation are indispensable for improving predictions of future changes in phenology.}, number={8}, journal={GLOBAL CHANGE BIOLOGY}, author={Marchin, Renee M. and Salk, Carl F. and Hoffmann, William A. and Dunn, Robert R.}, year={2015}, month={Aug}, pages={3138–3151} }
 @article{marchin_dunn_hoffmann_2014, title={Are winter-active species vulnerable to climate warming? A case study with the wintergreen terrestrial orchid, Tipularia discolor}, volume={176}, ISSN={["1432-1939"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84921938451&partnerID=MN8TOARS}, DOI={10.1007/s00442-014-3074-8}, abstractNote={In the eastern United States, winter temperature has been increasing nearly twice as fast as summer temperature, but studies of warming effects on plants have focused on species that are photosynthetically active in summer. The terrestrial orchid Tipularia discolor is leafless in summer and acquires C primarily in winter. The optimum temperature for photosynthesis in T. discolor is higher than the maximum temperature throughout most of its growing season, and therefore growth can be expected to increase with warming. Contrary to this hypothesis, experimental warming negatively affected reproductive fitness (number of flowering stalks, flowers, fruits) and growth (change in leaf area from 2010 to 2012) in T. discolor. Temperature in June-July was critical for flowering, and mean July temperature greater than 29 °C (i.e., 2.5 °C above ambient) eliminated reproduction. Warming of 1.2 °C delayed flowering by an average of 10 days and fruiting by an average of 5 days. Warming of 4.4 °C reduced relative growth rates by about 60%, which may have been partially caused by the direct effects of temperature on photosynthesis and respiration. Warming indirectly increased vapor pressure deficit (VPD) by 0.2-0.5 kPa, and leaf-to-air VPD over 1.3 kPa restricted stomatal conductance of T. discolor to 10-40% of maximum conductance. These results highlight the need to account for changes in VPD when estimating temperature responses of plant species under future warming scenarios. Increasing temperature in the future will likely be an important limiting factor to the distribution of T. discolor, especially along the southern edge of its range.}, number={4}, journal={OECOLOGIA}, author={Marchin, Renee M. and Dunn, Robert R. and Hoffmann, William A.}, year={2014}, month={Dec}, pages={1161–1172} }
 @article{hoffmann_marchin_abit_lau_2011, title={Hydraulic failure and tree dieback are associated with high wood density in a temperate forest under extreme drought}, volume={17}, ISSN={["1365-2486"]}, DOI={10.1111/j.1365-2486.2011.02401.x}, abstractNote={Catastrophic hydraulic failure will likely be an important mechanism contributing to large‐scale tree dieback caused by increased frequency and intensity of droughts under global climate change. To compare the susceptibility of 22 temperate deciduous tree and shrub species to hydraulic failure during a record drought in the southeastern USA, we quantified leaf desiccation, native embolism, wood density, stomatal conductance and predawn and midday leaf water potential at four sites with varying drought intensities. At the two driest sites, there was widespread leaf wilting and desiccation, and most species exhibited predawn leaf water potentials of ≤3 MPa and >60% loss of xylem conductivity in branches. Although species with high wood density were more resistant to cavitation, they had higher levels of native embolism and greater canopy dieback than species with low wood density. This unexpected result can be explained by the failure of species with dense wood to avert a decline in water potential to dangerous levels during the drought. Leaf water potential was negatively correlated with wood density, and the relationship was strongest under conditions of severe water deficit. Species with low wood density avoided catastrophic embolism by relying on an avoidance strategy that involves partial drought deciduousness, higher sensitivity of stomata to leaf water potential and perhaps greater rooting depth. These species therefore maintained water potential at levels that ensured a greater margin of safety against embolism. These differences among species may mediate rapid shifts in species composition of temperate forests if droughts intensify due to climate change.}, number={8}, journal={GLOBAL CHANGE BIOLOGY}, author={Hoffmann, William A. and Marchin, Renee M. and Abit, Pamela and Lau, On Lee}, year={2011}, month={Aug}, pages={2731–2742} }
 @article{marchin_zeng_hoffmann_2010, title={Drought-deciduous behavior reduces nutrient losses from temperate deciduous trees under severe drought}, volume={163}, ISSN={["1432-1939"]}, DOI={10.1007/s00442-010-1614-4}, abstractNote={Nutrient resorption from senescing leaves is an important mechanism of nutrient conservation in temperate deciduous forests. Resorption, however, may be curtailed by climatic events that cause rapid leaf death, such as severe drought, which has been projected to double by the year 2100 in the eastern United States. During a record drought in the southeastern US, we studied 18 common temperate winter-deciduous trees and shrubs to understand how extreme drought affects nutrient resorption of the macronutrients N, P, K, and Ca. Four species exhibited drought-induced leaf senescence and maintained higher leaf water potentials than the remaining 14 species (here called drought-evergreen species). This strategy prevented extensive leaf desiccation during the drought and successfully averted large nutrient losses caused by leaf desiccation. These four drought-deciduous species were also able to resorb N, P, and K from drought-senesced leaves, whereas drought-evergreen species did not resorb any nutrients from leaves lost to desiccation during the drought. For Oxydendrum arboreum, the species most severely affected by the drought, our results indicate that trees lost 50% more N and P due to desiccation than would have been lost from fall senescence alone. For all drought-deciduous species, resorption of N and P in fall-senesced leaves was highly proficient, whereas resorption was incomplete for drought-evergreen species. The lower seasonal nutrient losses of drought-deciduous species may give them a competitive advantage over drought-evergreen species in the years following the drought, thereby impacting species composition in temperate deciduous forests in the future.}, number={4}, journal={OECOLOGIA}, author={Marchin, Renee and Zeng, Hainian and Hoffmann, William}, year={2010}, month={Aug}, pages={845–854} }