Influcnces of Drought Stress on Photosynthetic Characteristics of Fragile Willow

Pot experiments were conducted with 5 watering treatments (watering to 80% field capacity, then stopping watering,followed by drought stress of 16 days,12 days,8 days,4 days and 0 day) on fragile willow saplings. Photosynthetic indicators of fragile willow were determined and analyzed under different drought stress. And the change of photosynthetic indicators of fragile willow after re-watering were observed. The results showed as follows:1) with the increase of drought stress, the net photosynthetic rate (Pn) of fragile willow saplings decreased significantly,stomatal conductance (Gs) and transpiration rate (Tr) overall decreased,and intercellular CO₂ concentration (Ci) decreased at first and then increased. 2) After re-watering the sapling for 72 and 120 hours, the net photosynthetic rate (Pn), stomatal conductance (Gs),the intercellular CO₂ concentration (Ci) and the transpiration rate (Tr) increased significantly. 3) Fragile willow adopted such a drought avoidance strategy as turning yellow,wilting,curling and drying off of leaves and wilting and sagging of terminal buds to cope with drought stress.