Effects of drought stress on photosynthesis physiology of Populus pseudo-simonii
干旱胁迫对杨树光合生理指标的影响

In this paper, the effects of drought stress simulated by PEG on the photosynthesis of Populus pseudo-simonii were monitored by gas exchange and chlorophyll fluorescence techniques. The results showed that in the early phase of drought stress, net photosynthetic rate (P(n)), transpiration rate (T(r)), stomata conductance (g(s)) , and intercellular CO2 concentration (C(i)) decreased with increasing stress, and the decrease of P(n) was mainly related to the decreased g(s). In the late phase, C(i) increased gradually, while F(v)/F(m) and F(v)/F(o) decreased significantly. POD activity increased in the early phase, but decreased in the late phase. All of these indicated that in the early phase of drought stress, stomata closure was the main factor limiting P. pseudo-simonii photosynthesis, while in the late phase, the main limiting factor was non-stomatal. A short period of drought stress induced the increase of protective enzyme activity, but a longer exposure to the stress resulted in the decrease of PS II efficiency and POD activity.