The interactive effect of precipitation on photosynthetic response and acclimation to temperature in two deciduous tree seedlings at the Boston Area Climate Experiment (BACE)

Background/Question/Methods

Climate change is projected to cause warming and changes in precipitation throughout many terrestrial ecosystems. Understanding the response of terrestrial plant species is important for predicting how ecosystems will respond to future changes. Many plant species can acclimate to changes in growth temperature by shifting their optimum temperature for photosynthesis. It is unknown whether this ability to acclimate is inhibited or enhanced by precipitation.  In this experiment, I measured the photosynthetic response to instantaneous changes in temperature in two tree seedlings, Quercus rubra and Acer rubrum, at the Boston Area Climate Experiment (BACE). BACE is a field-based, climate manipulation experiment in ecosystem in Waltham, MA. BACE has three different precipitation treatments: ambient, dry (-50% ambient rainfall), and wet (+50% ambient rainfall). Within each precipitation treatment ceramic heaters provide four warming treatments: ambient (+0^oC), low (+~1^oC), medium (+~2.5^oC), and high (+~4^oC). I measured the photosynthetic response to instantaneous changes in temperature in both species in each of the 12 plot types in order to derive the optimum temperature for photosynthesis (T_opt), the maximum photosynthetic rate given by the rate at T_opt (A_opt), and the sensitivity to instantaneous changes in temperature (b). These measurements were taken once early in the growing season (early May) and once late in the growing season (late July).

Results/Conclusions

Through this experiment I found that the tree seedlings acclimated to growth temperature on a seasonal basis (F=80.7, p<0.001), but did not acclimate to the temperature treatments (F=1.91, p=0.195). Precipitation treatment affected the acclimation potential of the tree seedlings to changes in growth temperature, although this response was not statistically significant (F=9.46, p=0.083). As precipitation increased the acclimation potential to growth temperature decreased. Acclimation potentials ranged from 0.46^oC per degree change in daytime plot temperature in the drought treatments to 0.32^oC per degree change in daytime plot temperature in the wet treatments. A_opt was significantly higher early in the growing season (May) compared to late in the growing season (July) (F=32.5, p<0.001). Plant were also more sensitive to instantaneous changes in temperature early in the growing season compared to late in the growing season (F=34.5, p<0.001). These results suggest that these species possess the ability to acclimate to changes in growth temperature on a seasonal basis and that precipitation may affect plant acclimation to growth temperature.