干旱区造林后幼树对土壤水分的生理响应过程对其进行水分管理并决定其成活的重要前提,以旱榆（Ulmus glaucescens）幼树为试材,采用盆栽自然失水和复水的方法,研究旱榆幼树形态、生理及光合特性对不同土壤失水程度及复水的响应过程,以期为栽培旱榆的水分管理提供理论依据。结果表明：（1） 在土壤失水较少时（土壤含水量为15%）,旱榆叶片相对含水量、叶绿素含量和水分利用效率表现出小幅升高,分别较试验前增加了14.8%、1.2%、43.2%;叶片的净光合速率、气孔导度、蒸腾速率呈明显下降趋势,分别较试验前降低了26.5%、27.1%、48.7%;（2） 土壤失水量严重时（土壤含水量为0%）,旱榆叶片相对含水量、叶绿素含量和水分利用效率大幅下降,分别较试验前下降了78.4%、65.4%、47.3%;叶片的净光合速率、气孔导度、蒸腾速率均表现为缓慢降低,分别较试验前降低了89.9%、83.3%、79.9%;光合速率下降的主要原因之一是气孔导度的变化。（3） 复水可以缓解土壤失水对旱榆的不利影响。因此,在土壤持续失水环境下,旱榆通过一系列形态、生理和光合特性的变化来适应土壤含水量的下降,表现出较强的耐旱性,旱榆栽植后如遇严重土壤失水的情况,复水可以缓解对其造成的危害。

The physiological responses of young trees to soil water after afforestation in arid areas are important factors in water management and their survival. To provide a theoretical basis for water management in the cultivation of Gansu elm trees (Ulmus glaucescens), we analyzed the responses of morphology, physiology, and photosynthetic characteristics of young Gansu elm trees to different degrees of soil water loss and rehydration by using the potted method under mimicking natural water loss and rehydration conditions. The results showed that relative water content, chlorophyll content, and water use efficiency of Gansu elm leaves increased slightly by 14.8%, 1.2%, and 43.2%, respectively when the soil water loss was less (15%). The net photosynthetic rate, stomatal conductance, and transpiration rate of leaves decreased significantly by 26.5%, 27.1%, and 48.7%, respectively. When soil water content was at its lowest point (0%), the relative water content, chlorophyll content, and water use efficiency of Gansu elm leaves decreased significantly that the relative water content decreased by 78.4%, 65.4%, and 47.3%, respectively. There was a gradual decrease in the net photosynthetic rate, stomatal conductance, and transpiration, by the values of 89.9%, 83.3%, and 79.9% which were lower than the corresponding rates before soil water loss. One of the main reasons for the decline in the photosynthetic rate was the change in stomatal conductance. Rehydration can alleviate the adverse effects caused by soil water loss in Gansu elm. Therefore, in the environment of continuous soil water loss, Gansu elm adapts to the decline of soil water content through a series of changes in morphology, physiology, and photosynthetic characteristics by showing strong drought tolerance. In the case of severe soil water loss after planting, rehydration can alleviate the damage to Gansu elm trees.