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Abstract
Our purpose was to examine the effects of mortality-inducing heat, drought, and low light on Pinus taeda L. seedlings over time. We monitored net photosynthetic assimilation and stem CO2 efflux (Fs) for 85 days, with periodic destructive harvests to measure biomass and nonstructural carbohydrates. We found a strong relationship between Fs and whole plant starch concentration among the treatments (P<0.01, R2=0.672). Seedlings in the heat treatment survived with significantly reduced nonstructural carbohydrate concentrations and growth, but significantly elevated Fs compared to seedlings in the control treatment. Seedlings in the drought and low light treatments had significantly reduced net assimilation and Fs compared to seedlings in the control treatment, and died after 10 weeks with severely depleted levels of starch. We conclude that carbon starvation played the primary role in their mortality, with water stress contributing to mortality in the drought treatment as well.