CO2 exchange under varying light intensities in some under- and overtemperature subtropical tree species.

CO2 exchange, transpiration and stomatal conductance of 39 subtropical tree species were studied under five light intensities at around atmospheric air temperatures found in subtropics during the active growth period of these species. Photosynthesis rates under different light intensities were strongly dependent on leaf to air temperature differences (ΔT). Based on ΔT, 39 species fell in two distinct categories namely, "undertemperature" and "overtemperature". Majority of the species in the former group were found to have relatively higher rate of photosynthesis, stomatal conductance, transpiration as well as water use efficiency. These species also showed higher light saturation for photosynthesis. The significance of the results is discussed in terms of adaptive potential in the two types of species.