基于年降水、生长季降水和生长季蒸散的高寒草地水分利用效率

Alpine grassland water use efficiency based on annual precipitation,growing season precipitation and growing season evapotranspiration

水分利用效率是深入理解生态系统碳、水循环间耦合关系的重要指标。以前研究青藏高原的水分利用效率多基于年降水量(AP)来分析,但植物对水分的利用主要在生长季。该研究采用以AP、生长季降水量(GSP)和生长季蒸散量(ETgs)分别计算的年降水利用效率(PUEa)、生长季降水利用效率(PUEgs)和生长季水分利用效率(WUEgs),分析了2000–2010年间青藏高原两种主要植被类型高寒草甸和高寒草原PUEa、PUEgs和WUEgs的差异及其与降水量、蒸散量和气温的关系。结果表明:(1)高寒草甸的PUEa、PUEgs均大于高寒草原,但两种草地类型的WUEgs无显著差别,这说明两种草地类型可能存在相似的内在的水分利用效率。(2)从年际动态来看,PUEa和PUEgs的波动范围相似,而WUEgs的波动范围更大,说明以蒸散为依据的WUEgs可能比PUEa和PUEgs更敏感,因而可能更好地反映生态系统的水分利用能力。(3)高寒草甸和高寒草原的PUEa、PUEgs和WUEgs分别与AP、GSP和ETgs呈单调递减趋势,表明3种水分利用效率均随降水量或蒸散量的增加而降低。高寒草原的3种水分利用效率中仅WUEgs随着气温的增加而增加,而高寒草甸的3种水分利用效率均与气温无显著关系,这说明相比高寒草甸,高寒草原的水分利用效率对气温更加敏感。

Aims Water use efficiency （WUE） is an important parameter to understand the coupling between the water, and carbon cycles of terrestrial ecosystems. Previous studies on the grassland ecosystem WUE on the Qinghai-Xizang Plateau mainly based on annual precipitation （AP）. However, vegetation water use mainly occurs in growing sea- son. Therefore, we aimed to explore the differences of ecosystem WUE between alpine meadow and alpine steppe, and the relationships between ecosystem WUE and environmental factors from 2000 to 2010, using annual pre- cipitation use efficiency （PUEa）, growing season precipitation use efficiency （PUEgs）, growing season water use efficiency （WUEgs） based on AP, growing season precipitation （GSP） and growing season evapotranspiration （ETgs ） respectively. Methods Combining satellite-derived above-ground net primary productivity （ANPP）, satellite-derived evapotranspiration and meteorological data from 2000 to 2010, we calculated PUEa （ANPP/AP）, PUEgs（ANPP / GSP） and WUEgs（ANPP / ETgs） to find the differences of PUEa, PUEgs and WUEgs between alpine meadow and alpine steppe. Moreover, we explored the relationships between PUEa, PUEgs or WUEgs and precipitation （or evapotranspiration） or air temperature. Important findings We found that （1） the PUEa and PUEgs of alpine meadow were higher than that of alpine steppe, but there were no significant difference between WUEgs of the two grassland types, indicating that there may be similar intrinsic water use efficiencies of the two grassland types. （2） The inter-annual variation of PUEa and PUEgs were similar while WUEgs showed a larger fluctuation, implying that ET-based WUEgs was more sensi- tive than precipitation-based PUEa and PUEgs, therefore WUEgs is a better indicator of ecosystem water use effi- ciency than PUEa or PUEgs. （3） The PUEa, PUEgs and WUEgs were negatively correlated with AP, GSP and ETgs respectively, reflecting a consistency of the three water use efficiency measurements. In the alpine steppe, only WUEgs was observed positively correlated with air temperature among the three measurements, but in the alpine meadow, no significant relationships between water use efficiency and air temperature was detected, suggesting that the WUEfs of alpine steppe was more sensitive to air temperature than that of alpine meadow.