小叶杨“小老树”生长季内水分特征及光合能力

Water Metabolism Characters and Photosynthesis Capacity of Old Small Populus Trees in Growth Season

以水分为主导因子所形成的小老树在生长季内有自身的水分特征，水分不足使叶片水势、蒸腾速率和光合能力均有所下降；叶片自身也发生了适应性变化：叶子变厚、单叶面积减小，总光合能力下降，最终表现在同化物累积量低。

There existed special water metabolism characters in old small populus trees in growth season caused dominantly by water deficit. A a result,water potential of the leaves,the rate of transpiration as well as photosynthesis decreased. Meanwhile,adaptative changes occurred in leaf itself:an increase.in leaf thickness and decreases in single leaf area and total photosynthesis capacity,which finally resulted in a decrease of biomass accumulation.These were physiological reasons that old small trees formed.