中文摘要：

分析干旱区不同林龄胡杨对脉冲式降雨的响应,对制定气候变化下胡杨保育恢复策略具有重要意义。通过对降雨前、后黑河下游不同林龄胡杨木质部水及其不同潜在水源稳定同位素组成（δD、δ18O）的测定,分析不同深度的土壤水、地下水和降水对胡杨水分利用的贡献比例,并结合胡杨样地土壤剖面含水量的变化,探讨降雨前、后不同林龄胡杨水分利用变化及对脉冲式降雨的响应。结果发现：1降雨前、后胡杨幼苗木质部的δ18O值变化较大,分别为-3.498‰和-7.928‰,而胡杨成熟木木质部的δ18O值变化不大,分别为-7.202‰和-7.225‰;2降雨前、后胡杨幼苗对不同水源水分利用变化较大,降雨前主要利用0～30 cm的土壤水,利用比例达88%～90%,平均值为89.9%,对地下水的利用仅为2.9%。降雨后对降水的利用最高达60%,平均值为19%;降雨前、后胡杨成熟木都主要利用地下水和深层土壤水。

英文摘要：

Stable isotopes of oxygen and hydrogen were considered to be a good tool and have been used to identify the source of water,because different source of water possess different oxygen or hydrogen isotope signatures. Until now,several approaches have been developed to quantify the contribution of different water source to plants based on the isotopic mass-balance principal. We researched the response of Populus euphratica for different ages to rainfall pulsation,playing a key role in formulating the conservation strategy of Populus euphratica under the climate change. In this study,we analyzed the soil water of different depth,groundwater and precipitation on the contribution ratio of plants,combined with the change of soil water content,discussed the response of Populus euphratica to rainfall pulsation before and after rain,based on the composition of the stable oxygen and hydrogen isotope（ δ18O,δD）of the xylem of Populus euphratica in different ages and different potential water sources in the lower reaches of the Heihe River. The results showed that： 1 There were significant differences of δ18O value in the xylem of young Populus euphratica before and after rain,-3. 498‰ and-7. 928‰,but there were no significant differences of mature Populus euphratica,-7. 202‰ and-7. 225‰; 2 Water source absorption ratio changes greatly of young Populus euphratica before and after rain. Before rain,the main absorption of 0-30 cm of soil water,the using proportion is as high as 88%-90%,the mean value of 89. 9%,only using 2. 9% underground water. After the rain,the use of precipitation is up to 60%,the mean value of 19%; The main water sources of mature Populus euphratica were underground water and deep subsoil water. The depth range of the mature Populus euphratica is wider than young Populus euphratica.