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1 December 2016 Ecophysiological Responses of Tsuga canadensis (Eastern Hemlock) to Projected Atmospheric CO2 and Warming
Lily Wilder, Jennifer N. Boyd
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Tsuga canadensis (Eastern Hemlock) is a keystone tree species currently experiencing high mortality in southeastern US forests due to Hemlock Woolly Adelgid (Adelges tsugae; HWA) invasion. Investigating the impacts of concurrent climate change on Eastern Hemlock is important given its potential direct effects on this species and possible interactions of climatic factors with the continued spread of HWA. We conducted a 2-factorial experiment in controlled-environment growth chambers to test for the main effects and interactions of projected atmospheric CO2 concentrations and transitional-season warming on gas-exchange traits of Eastern Hemlock saplings collected from a northern Georgia field site. We hypothesized that elevated CO2 would increase photosynthesis and that warming would not influence photosynthesis, given the demonstrated capacity for photosynthetic temperature-acclimation in this species. Saplings in elevated CO2 exhibited ∼30% greater leaf-level photosynthesis (A) and ∼35% greater maximum light-saturated photosynthesis (Amax) than saplings in ambient CO2. In contrast, warming did not influence A or Amax as a main effect. However, significant treatment interactions suggest that the response of Eastern Hemlock to rising CO2 could be impacted by associated warming. Specifically, when saplings were grown in elevated CO2, warming was associated with reductions in Amax, rate of respiration in the dark, and stomatal conductance, but these variables were not influenced by warming when combined with ambient CO2. An increase in the light-saturation estimate with elevated CO2 across temperature-treatment levels indicates that CO2 can be a limiting factor for Eastern Hemlock, but significant treatment interactions suggest that the capacity for this species to utilize increased CO2 may be impacted negatively by warming.

Lily Wilder and Jennifer N. Boyd "Ecophysiological Responses of Tsuga canadensis (Eastern Hemlock) to Projected Atmospheric CO2 and Warming," Southeastern Naturalist 15(4), 697-713, (1 December 2016).
Published: 1 December 2016
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