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在荒漠生态系统中,水分是植物生长和植被动态的一个限制因子.来自深层土壤或地下水相对稳定的水分对于干旱条件下植物的生存至关重要.在荒漠生态系统中,保护和恢复濒危植物的根本在于理解它们的水分利用策略,例如蒙古高原的沙冬青(Ammopiptanthus mongolicus).本论文通过稳定氢、氧同位素技术研究了沙冬青和与其伴生的两种灌木黑沙蒿(Artemisia ordosica)和旱蒿(Artemisia xerophytica)的主要水分来源;利用IsoSource模型计算了不同水分来源对每个物种的贡献,并通过比较3种灌木叶片δ13C值和和其根系分布探讨了3种灌木的长期水分利用策略.结果表明,沙冬青依赖地下水和150-200cm深层土壤水,前者几乎贡献其水源的一半.黑沙蒿主要利用150-200 cm深层土壤水,但是夏季和秋季也利用100 cm以内的浅层土壤水.旱蒿主要利用150-200 cm深层土壤水和地下水,后者对其总水源的贡献率大约为30％-60％.3种灌木具有双型根系或深根系,这些根系特征与其水分来源一致.常绿植物沙冬青的叶片δ13C值高于两种落叶蒿属灌木,这可能使其在适应荒漠生态系统中具有优势.因此,地下水是干旱年份蒙古高原濒危灌木沙冬青的一个主要水源,而且沙冬青和两种蒿属灌木竞争深层土壤水和地下水.“,”Aims In desert ecosystems,water is a restricting factor for plant growth and vegetation dynamics.The relatively stable water source from deep soil profile or groundwater is important for plant survival during drought.Understanding water use strategy of endangered species,in desert ecosystem is essential for their conservation and restoration such as Ammopiptanthus mongolicus on the Mongolian Plateau.Methods The stable isotope method of δD and δ18O was used to examine the main water sources of A.mongolicus and two companion shrubs,e.g.Artemisia ordosica and Artemisia xerophytica.The contribution of different water sources to each species was calculated by IsoSource model.Leaf δ13C was used to compare long-term water use efficiency of three shrubs.Soil moisture and root distribution of three shrubs was measured to explain plant water use strategy.Important Findings The results showed that A.mongolicus relied on groundwater and 150-200 cm deep soil water,with the former contributing to almost half of its total water source.Artemisia ordosica mainly used 150-200 cm deep soil water,but also used shallow soil water within 100 cm in summer and autumn.Artemisia xerophytica mainly used 150-200 cm deep soil water and groundwater,with the latter contributing to about 30％-60％of its total water source.The three shrubs had dimorphic or deep root systems,which are in accord with their water sources.The WUE in the evergreen shrub A.mongolicus was higher than in two deciduous Artemisia shrubs,which may be an adaptive advantage in desert ecosystem.Therefore,groundwater is an important water source for the endangered shrub A.mongolicus in a drought year on Mongolian Plateau.Ammopiptanthus mongolicus and two Artemisia shrubs competed for deep soil water and groundwater.