Strong impacts of autumn phenology on grassland ecosystem water use efficiency on the Tibetan Plateau

Abstract Vegetation phenology is a commonly used indicator of climate-vegetation interactions, which also plays a crucial role in regulating gross primary productivity (GPP), evapotranspiration (ET) and ecosystem water use efficiency (WUE, defined as the ratio between GPP and ET). Actually, quantitative evaluation of the impact of phenology on WUE is critical yet lacking. In this study we detected the interannual variations of autumn WUE, GPP and ET and conducted Redundancy analysis (RDA) to quantitatively assess their responses to autumn end of growing season (EOS) in the grassland ecosystem across the Tibetan Plateau. Our study found that the delayed EOS increased the daily mean GPP but meanwhile increased the ET in autumn, rather than enhanced the WUE. Over the entire Tibetan Plateau, the daily GPP and ET in the autumn of the steppe were dominated by the delayed EOS, with the explanatory power of EOS to GPP and ET of 75.90% (P