塔里木荒漠河岸林建群种适应土壤干旱的用水策略与机理研究

The development and existence of desert riparian forest controlled the structure, function and environmental change of desert ecosystem in Tarim. Populus euphratica Oliv and Populus pruinosa Schrenk were the constructive species of Tarim desert ecosystem and were be research objects,and soil water-vegetation system was be centre.From the integration of ecophysiological response and individual morphology adjustment，Dynamic response of photosynthetic characteristics,transpiration and water potential,water use efficiency,drought resistance characteristics，stomatal behavior and water optimal regulation，biomass allocation and root characteristics were studied under soil water gradient to analyse feedback adjustment mechanism and adaptative change of water use strategy.The objective is to elucidate the internal conforming coupled mechanism of ecophysiology and morphology ,and interspecific difference of adaptative mechanism ,and expounded the different water use strategies and ecophysiological adaptation mechanisms of two tree species under water stress.The quantitative relation of ecophysiology,morphology characteristics and water potential,soil water content were analysed with multivariate statistical methods,and to demonstrate the optimal soil water content(groundwater depth) and critical soil water content(depth of groundwater table) for population survival.According to above results, the project selected different tree species to plant in different fitness habitat and optimal configuration model of different tree species in different habitats. The research results will provide scientific theory to restore and rebuild the degraded ecosystem and strategy of ecological conservation for desert riparian forest in Tarim basin.

荒漠河岸林的存在与发展决定着塔里木荒漠生态系统的结构、功能与环境变迁。以塔里木荒漠河岸林建群种-胡杨、灰胡杨为研究对象，以土壤水分-植被为中心，在原始生境自然形成的地下水位梯度和人工模拟水分梯度下，整合植物生理生态响应与个体形态调整研究2树种气体交换特性、蒸腾耗水特性、枝叶水势、水分利用效率与水分利用格局、抗旱生理代谢物质、气孔行为与水分利用调节、生物量分配与根系变化等沿水分梯度变化的响应与反馈调节机制及水分利用策略的变化，阐明2树种生理生态响应与个体形态调整之间的内在耦合协调机制与种间适应机制的差异，确定2树种生理生态、个体形态特征与枝叶水势、土壤水分（地下水位）的定量关系，揭示2树种适应土壤干旱的生理生态机理与用水策略及种间的差异性、生长的适宜和临界土壤水分（地下水位），筛选出适合不同生境的适生树种与植被配置结构，为塔里木荒漠河岸林生态保育、退化生态系统的恢复与重建提供科学的理论依据。

本项目以塔里木荒漠河岸林建群种-胡杨、灰胡杨为研究对象，系统研究2建群树种沿水分梯度变化的生理生态响应和反馈调节机制，揭示比较二者适应土壤干旱的生理生态机理与种间用水策略的差异性，为干旱区水资源的合理有效利用、退化生态系统的恢复与重建提供科学的理论依据。取得研究结果如下：（1）胡杨属高光合、低蒸腾、高WUE和低水势忍耐脱水型树种，气孔调节能力与抗逆能力较灰胡杨强，灰胡杨对水分的需求较高。（2）胡杨、灰胡杨蒸腾速率(Tr)对气孔导度(Gs)响应敏感度高于水汽压差(VPD)，不同时段气孔的调节机制不同，上午气孔调节为前馈式反应，下午为反馈式反应。（3）灰胡杨以积累大量游离脯氨酸来增强其渗透调节能力，增大根系吸水能力，另一方面通过叶片表面密被的绒毛反射强光辐射，并通过提高蒸腾失水降低叶温来抵御干旱对其光合机构的破坏；胡杨主要以大量积累可溶性糖和K+来降低细胞渗透势并维持水势的基本稳定，并通过较高的保护酶活性维持膜结构的基本稳定；同时胡杨采取缩窄光照生态幅、降低光能的吸收和减少呼吸消耗的生态对策积极抵御干旱逆境。（4）随干旱程度的加剧，胡杨水分利用效率高于灰胡杨，其气孔调节起了非常重要的作用。（5）整合胡杨、灰胡杨生理生态与形态调整，提出既能维持胡杨、灰胡杨种群有较高的光合效率和WUE及正常生长的适宜土壤水分分别为田间持水量的45%—50%、60%—65%。土壤水分低于25%田间持水量条件下灰胡杨幼苗死亡，而胡杨幼苗则能生长，但生长受严重抑制。胡杨幼苗临界土壤水分含量为20%—25%，灰胡杨为30%—35%。胡杨、灰胡杨种群合理生长的地下水位为＜4m，5.5 m为其生理、生长显著受抑的地下水位，种群明显衰退。（6）综合2树种各生理生态响应与形态特征变化，表明胡杨的抗逆能力比灰胡杨强，据此提出塔里木荒漠生态系统植被恢复应优先选用胡杨为造林树种，对绿洲外围植被恢复、林区规划、退耕还林还草与防护林建设等方面有实践指导作用。