Predicting the future distribution of plants requires a mechanistic understanding of how plant scope with their new environmental conditions under a changed climate.We examined the effects of elevated carbon concentration([CO2]) and elevated Tsoil on the physiological responses to ligh to fashade-tolerant woody species,mountain maple(Acer spicatum L.). Seedlings were exposed to ambient and elevated[CO2] (392mol mol−1 vs. 784mol mol−1), current and elevated soil temperatures(Tsoil 17 vs.22 ◦C)at high and low(100%vs.30%)light conditions for one growing season.It was found that elevated Tsoil stimulatednet 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 Tsoil and by 48% at the current Tsoil. The effect of elevated Tsoil 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 [CO2]. Ourdataindicatethattheelevated[CO2] markedly increased nitrogen(N) allocation to the photochemical apparatus of A in seedlings grown under the high-light condition.