中文摘要：

水分是干旱、半干旱地区植物生长最主要的限制因子.为了探究较大降水事件后两种常见人工固沙植物柠条与油蒿的水分来源差异,分析降水、土壤水、地下水和植物茎水的氢氧稳定同位素特征,并采用直接对比法和多元线性混合模型对植物水分来源进行分析.结果表明：沙坡头地区大气降水线方程为δD=7.83δ^（18）O＋5.64（R2=0.91）.降水δ^（18）O值的变化范围较大,具有明显的季节变化规律;生长季前期与后期δ^（18）O值相对较高,生长旺盛期δ^（18）O处于较低水平.浅层土壤水δ^（18）O值变化范围较大,随土层深度的增加,土壤水δ^（18）O值变幅减小且呈减小趋势.在降水后第一天,柠条和油蒿分别对40～80与20～60 cm土层土壤水利用比例较高,利用比率分别为56.1%和56.4%.降水一周后,柠条与油蒿都不同程度地增加了对浅层土壤水的利用比例.柠条和油蒿对0～40和0～20 cm土层土壤水分利用率分别增加了12.5%和10%.表明在较大降水事件后,柠条和油蒿会通过调整水分利用策略来积极适应干旱环境.

英文摘要：

Water is a major limiting factor for plant growth in arid and semi-arid regions.To find out the main sources of water for two artificial sand-fixation plants（ Caragana korshinskii and Artemisia ordosica）,we analyzed the characteristics of hydrogen and oxygen stable isotopes in water molecules of rainfall,soil water and xylem water.To analyze water sources of these two plants,we used a direct comparison method and a multi-variate mixed linear model.The results showed that an equation of local meteoric water line in Shapotou was δD = 7.83δ^（18）O＋5.64（ R2= 0.91）.The value for rainfall δ^（18）O varied during plant-growing season,which was higher in the beginning and end of growing season,and lower in the peak of growing season.The value for soil water δ^（18）O in the upper layers changed dramatically.The change range became smaller in the deeper soil layer.C.korshinskii had a greater efficiency（ 56.1%） in utilizing soil water in 40-80 cm soil layer.A.ordosica had a utilizing efficiency of 56.4% in 20-60 cm soil layer.A week after rain event,C.korshinskii and A.ordosica showed a higher efficiency in upper soil water.C.korshinskii showed an increase of12.5% in utilizing soil water in 0-40 cm soil layer and A.ordosicas showed an increase of 10% in utilizing soil water in 0-20 cm layer.These results suggested that C.korshinskii and A.ordosica changed their water use strategy after large rainfall events,which might enable them to more easily adapt to arid environment.