Water use efficiency response of plant communities to drought in different growing periods in alpine meadow

The drought is becoming more frequent and severe with changing precipitation pattern in the future. How the water use efficiency responds to drought in different periods during the growing season has become a key scientific issue to explore the response mechanism of carbon and water cycle coupling process to drought in alpine meadow ecosystem. This project focused on the response mechanism of alpine meadow ecosystem productivity to drought and the relationship between productivity, evapotranspiration (or rainfall) and water use efficiency under simulated drought events in the early and middle growth seasons, and discuss the response mechanism of water use efficiency of alpine meadow ecosystem to drought. The result showed that (1) the delayed green-up under early growing season drought and advanced withered date under middle growing season drought occurred in graminoids, weeds and plant community, which indicated ‘escape strategy’ to drought. (2) the effect of advanced withered date was divergent among graminoid and weeds on the aboveground net primary production, which may lead to a stronger resistance of community productivity to middle growing season drought. (3) besides soil water deficit, the limited accumulation of aboveground biomass inhibited the physiological process of carbon exchange in alpine meadow community either. However, the carbon exchange process presented an over compensation mechanism, and the material distribution strategy may vary after rainfall restoration. (4) early growing season drought had no significant effect on water use efficiency of alpine meadow community (p > 0.05), while water use efficiency increased significantly under middle growing season drought (p < 0.05). The main reason is that the plant community is more sensitive to early growing season drought, which depressed the aboveground biomass, while aboveground productivity of alpine meadow plant community has stronger resistance to middle growing season drought. This project studied the response mechanism of alpine meadow ecosystem to extreme drought events in different periods, which has great scientific significance to the study of ecosystem response to extreme climate events, and provides a scientific basis for predicting and simulating the response of alpine meadow ecosystem in Northern Tibet to climate change in the future, especially the change of precipitation pattern.