中文摘要：

系统水分利用效率（WUE）是高寒草甸生态系统碳水耦合及植被演替的重要指标,但其时间格局和主要环境因素仍不清楚。基于青藏高原东北隅高寒嵩草草甸的涡度相关仪器观测的CO2和H2O通量数据,分析了2015年植被生长季（4月-10月）的系统水分利用效率（总初级生产力/植被蒸腾）的变化特征和主要环境影响因子。结果表明,总初级生产力（GPP）和植被蒸腾具有显著的单峰季节趋势,与群落叶面积指数（LAI）显著相关。生长季日均WUE为3.24g C·kg H2O（-1）,没有显著的季节动态,呈现出＂保守型＂的特征。增强回归树的结果表明光合光量子通量密度（PPFD）、饱和水汽压差（VPD）和净辐射（Rn）是其主要调控因素,与WUE显著指数负相关（r2〉0.40,p〈0.001）。

英文摘要：

Alpine meadow ecosystem water use efficiency was an important indicator for understanding the coupling the water and carbon cycles while the temporal patterns and controlling factors of water were not fully clear. We collected CO2 and H2O flux dataset measured by eddy covariance technique over an alpine Kobresia meadow on the northeastern Qinghai - Tibetan Plateau, and analyzed the temporal pattern of daily WUE and its main environmental factors during plant growing season from April to October. The results showed that the seasonal variations of gross primary production （GPP） and plant transpiration （T） were unimodal and were predominately controlled by leaf area index （LAI）. The daily WUE during growing season was 3, 24gC , kgH2O -1 and did not fluctuate with season development, which indicated that WUE of alpine meadow was relatively conservative. Boosted regression trees （BRT） showed that photosynthetic photon flux density （PPFD）, vapor pressure deficit （VPD） and net radiation （Rn） accounted for the more relative contribution of variations of daily WUE, Those factors correlated exponential negatively with WUE （r2 〉 0.40, p 〈 0.001 ）.