Ecosystems water use patterns of Quercus variabilis and Grewia biloba based on stable hydrogen and oxygen isotopes in the south aspect of Taihang Mountains Water utilization sources of Alnus nepalensis in the water source area of Yuanyang terrace Water sources of five dominant desert plant species in Nuomuhong area of Qaidam Basin Study on Hydrogen and Oxygen Stable Isotopes in Precipitation in Wolong Nature Reserve,Sichuan Province