水分胁迫对梭梭叶片气体交换特征的影响

对梭梭叶片在自然水分胁迫下的气体交换特征进行了研究。结果表明，梭梭在旱季与雨季时的光合作用日变化曲线均呈双峰型，具有光合午休现象。在旱季，植物气孔开度减小，从而减少了水分的散失，而严重的水分胁迫引起叶肉细胞光合活性的降低。根据Farquhar和Sharkey提出的关于区分光合作用的气孔限制与非气孔限制的两个标准，在水分亏缺较严重的旱季，光合午休主要是由非气孔因素引起的；而在雨季，光合午休主要是由气孔因素导致的。通过光合午休、梭梭叶片1天中的气体交换主要发生在上、下午光合较高而蒸腾较低的那部分时间里，从而使水分利用效率比较高，这是梭梭对干旱生境的一种适应方式。

Effects of Water Stress on Gas Exchange Characteristics of Haloxylon Ammodendron Leafs

The photosynthetic characteristics of Haloxylon ammodendron under natural water stress was studied. The results showed that the net photosynthetic rate displayed a two-peaked diurnal curve in both the dry season and the wet season. The stomatal conductance in the dry season was lower than that in the wet season. The plant diminished the loss of water by decreasing stomatal conductance. Under severe water stress, the photosynthesis activity of mesophyll cells was decreased. According to the two criteria discriminating the stomatal limitation of photosynthesis suggested by Fuqua and Sharkey, the midday depression of photosynthesis in the dry season was predominantly due to the photosynthetic capacity of mesophyll cells. In the wet season, it was predominantly due to stomatal limitation. Midday depression is an important adaptive strategy for Haloxylon ammodendron leafs to avoid water loss under the desert environment.