Water plays an important role in plant growth and distribution,and its resource selection is an important process in the botanical cycle.Although precipitation is the ultimate water source for all plants,factors like evaporation,altitude,geological aquifer features,and soil water characteristics may all influence values of stable hydrogen and oxygen isotopes (δD,δ18O).The water source used by a plant can be revealed by comparing the water δD and δ18O values from stem xylem with those from the available water sources.Subalpine shrubland is an important vegetation type in the Qilian Mountains,and has high water-conservation capacity.Studies on the water source of the dominant plants of the subalpine shrubland in the Qilian Mountains contribute to understanding the water cycle and eco-hydrological process of subalpine shrubland.In this study,six species of dominant subalpine shrub plants in the eastern Qilian Mountains were selected to analyze the water sources of different plants in the same biotope landscape and the water source changes of the same plant in different growth stages using multivariate linear mixed models (Isosource).The local meteoric water line (LMWL) equation was δD =7.775 δ18O + 12.34 (R2=0.871,P ＜ 0.001),which showed that the study area has the characteristics of strong evaporation,low temperature,and high humidity.The results showed that the six dominant plant species mainly used precipitation during the entire growth season.Soil water from 0 to 10 cm was the second major water source.The contribution of groundwater was the lowest.The six dominant plant species changed the proportions of different water sources utilized during the growth season.In July,the six dominant plant species mainly used precipitation and shallow soil water.The contribution rates of precipitation and 0-10cm soil water to Spiraea salicifolia L.,Rhododendron capitatum Maxim,and Rhododendron thymifolium Maxim were similar,but the other three species mainly used precipitation.In August,the main water source of all six species was precipitation.The use of soil water in each soil layer from 10 to 80 cm by R.thymifolium and S.salicifolia decreased over time,whereas that by the other four plants first increased and then decreased with depth.The ability of S.salicifolia and R.capitatum to utilize soil moisture was strong.The use of groundwater by R.capitatum was higher than that by other plants.%选取祁连山东部亚高山灌丛的6种优势植物:山生柳(Salix oritrepha Schneid)、头花杜鹃(Rhododendron capitatum Maxim)、绣线菊(Spiraea salicifoliaL.)、高山柳(Salix cupularis)、千里香杜鹃(Rhododendron thymifolium Maxim)和金露梅(Potentilla fruticosa Linn),利用稳定同位素技术及多元线性混合模型(Isosource)定量分析典型高寒区植物的水分来源.结果表明:乌鞘岭地区7-8月的大气降水线为δD=7.775δ180+ 12.34(R2=0.871,P＜0.001),反映了该地区气温低,湿度大的气候特点;6种优势植物的水分来源主要是降水,其次为0-10cm土壤水,地下水对各种植物水分的贡献率最小;6种优势植物对各水源的利用在不同时段有差异,7月份主要利用降水和浅层土壤水,而8月份各种植物的主要水源均为降水;绣线菊和头花杜鹃利用土壤水分的能力较强,头花杜鹃对地下水的利用率高于其他植物.
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