Effects of elevated [CO2] and soil temperature on photosynthetic responses of mountain maple (Acer spicatum L.) seedlings to light

Predicting the future distribution of plants requires a mechanistic understanding of how plants cope with their new environmental conditions under a changed climate. We examined the effects of elevated carbon concentration ([CO2]) and elevated T-soil on the physiological responses to light of a shade-tolerant woody species, mountain maple (Acer spicatum L.). Seedlings were exposed to ambient and elevated [CO2] (392 mu mol mol(-1) vs. 784 mu mol mol(-1)), current and elevated soil temperatures (T-soil 17 vs. 22 degrees C) at high and low (100% vs. 30%) light conditions for one growing season. It was found that elevated T-soil stimulated net photosynthesis (A) by 18% in the low-light treatment but tended to reduce A in the high-light treatment. Elevated [CO2] increased A by 100% under the elevated T-soil and by 48% at the current T-soil. The effect of elevated T-soil also varied with [CO2]: it increased A by 13% under the elevated [CO2] but reduced A by 17% under the ambient [CO2]. We observed a significant increase in the instantaneous water-use efficiency of photosynthesis (IWUE) in response to the high-light treatment under the elevated [CO2] but not under the ambient [CO2]. Our data indicate that the elevated [CO2] markedly increased nitrogen (N) allocation to the photochemical apparatus of A in seedlings grown under the high-light condition. These results suggest that the predicted increases in atmospheric [CO2] will likely, enhance the growth of mountain maple in canopy gaps in the forest, while the predicted elevated T-soil will negate the benefit of high-light conditions. (C) 2014 Elsevier B.V. All rights reserved.