中文摘要：

栓皮栎是北京山区分布范围较广的典型阔叶树种,揭示其在生长季内不同土壤水分条件下的水分利用策略具有重要意义。本研究通过测定分析生长季内栓皮栎枝条水、土壤水和地下水的δD和δ18O值,并利用多元混合模型（Iso-source软件）计算栓皮栎对土壤水或地下水的利用比例,再结合叶片水势、气孔导度（Gs）、光合速率（Pn）和蒸腾速率（Tr）等生理生态因子同步观测,了解北京山区优势乔木树种栓皮栎在生长季内的水分来源及生理生态适应。结果表明：栓皮栎对不同深度土壤水分利用比例具有季节变化特征,4—6月,栓皮栎主要利用表层0～30 cm土壤水、深层80～100 cm土壤水和地下水,且对3者的水分利用较为均衡;进入7—8月,栓皮栎的水分来源从表层土壤水逐步转向深层土壤水和地下水,对表层的土壤水利用较少;雨季过后进入降雨较少的9—10月,栓皮栎的水分来源又从深层土壤水和地下水逐步转向表层土壤水。生长季内土壤水分的季节波动明显影响栓皮栎的叶片气体交换过程,林地水土条件较好时,栓皮栎较高的气孔导度使其水分利用效率较低;当林地水分条件变差,栓皮栎能通过降低气孔导度减少水分损失来获得较高的碳同化速率,维持较高的水分利用效率来适应干旱生境,表现出较强的适应能力。

英文摘要：

In order to understand water source of the dominant tree species Quercus variabilis and its ecophysiological adaptation during growing season in Beijing mountainous area,we studied the water use strategy of Q. variabilis under different soil moisture conditions during growing season. We employed the Iso-source software and measured the δD and δ18O in branches,soil and groundwater to clarify their water source during growing season,by combining with ecophysiological factors,such as leaf water potential（ ψ）,stomatal conductance（ Gs） and water use efficiency（ WUE）. The results showed that the Q.variabilis had different water sources with season varying： from April to June,it mainly utilized surface soil（ 0- 30 cm） water,deep soil（ 80- 100 cm） water and groundwater in a much balanced pattern; in July and August,the water source gradually shifted to deep soil water and groundwater,and almost no surface soil water was used; during September and October after the rainy season,the water source gradually shifted to the shallow layer soil water. During growing season,the seasonal fluctuation of soil moisture significantly affected Gsof Q. variabilis. Under good soil water conditions,Gswas higher and WUE is lower; under serious water shortage,Q. variabilis can reduce stomatal conductance to decrease water loss and obtain higher carbon assimilation rate and maintain higher water use efficiency,in order to adapt to the arid condition.