沙漠腹地胡杨不同生长时期的地表水和地下水利用机制

荒漠河岸林是内陆河天然绿洲的主体，它的生长和分布与水分来源密切相关。本项目拟在克里雅河尾闾沙漠腹地的达理雅博依绿洲内，以荒漠河岸林建群种胡杨为对象，将其划分为幼苗、幼树、成熟木和过熟木共4个生长时期，之后采集各阶段胡杨小枝木质部、土壤、河水和地下水的样品，测试其中的氧稳定同位素比率(δ18O)，对比获得各阶段胡杨的主要吸水层位。同时测定各阶段胡杨叶片的光合、水分生理以及叶片的碳稳定同位素值（δ13C）。最后利用IsoSource线性混合模型和δ13C值分别确定各阶段胡杨体内的水分来源和比例，以及地表水和地下水位变化对胡杨水分来源、生理特性和长期水分利用效率的影响。本项目的研究成果可能对揭示胡杨生存的合理地下水位波动范围，阐明极端干旱区胡杨的水分利用策略，指导天然绿洲的植被保护和修复提供科学依据。

Desert riparian forests are the main body of natural oases of inland rivers，and its growth and distribution are closely related with water use sources. Populus euphratica is a main tree species that forms natural riparian forests in arid and semi-arid areas. This research is planned to carry out in the Daliyaboyi oasis which is located at the delta area of the Keriya River in the Taklimakan desert in north western China. P. euphratica forests can be grouped into four stages, which are seedling, sapling, mature and overmatured, respectively. The plant xylem water of each stage, soil moisture, stream water and groundwater will be taken to test the stable oxygen isotope ratio (δ18O) for each water sample. The δ18O of plant xylem water and soil water will be compared to estimate the dominant depth of root water uptake, and the linear-mixed model called “IsoSource” will be applied to determine plant water sources and quantify their proportions. Meanwhile, the gas-exchange characteristics, water potential and stable carbon isotope ratio (δ13C) of leaves of P. euphratica will be analyzed to evaluate the impact of variation of surface water and groundwater on water use, physiological condition and water use efficiency of P. euphratica. Our research may reveal proper groundwater depth to the survival of P. euphratica, illuminate the water use strategy of P. euphratica in the extreme arid region, and provide guide to vegetation protection and restoration in the natural oasis.