Alpine grassland water use efficiency based on annual precipitation, growing season precipitation and growing season evapotranspiration
MI Zhao-Rong,CHEN Li-Tong,ZHANG Zhen-Hua,HE Jin-Sheng
Chin J Plan Ecolo. 2015, 39 (7):
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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 season. 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 precipitation 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 sensitive than precipitation-based PUEa and PUEgs, therefore WUEgs is a better indicator of ecosystem water use efficiency 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 WUEgs of alpine steppe was more sensitive to air temperature than that of alpine meadow.