The divergent impact of phenology change on the productivity of alpine grassland due to different timing of drought on the Tibetan Plateau

Droughts are predicted to become more frequent and persist for longer periods in the future, especially in alpine regions due to climate change. However, the association mechanism between plant productivity response to drought timing and phenology in the alpine grassland of the Tibetan Plateau is unclear. We conducted manipulative drought experiments on early growing season drought (ED) and middle growing season drought (MD) to determine the impacts of drought timing on the alpine grassland. The results showed ED significantly delayed the green-up of the community vegetation (8.20%, p < .05). However, MD advanced the withered date of the community vegetation (-2.98%, p < .05). ED and MD depressed the growing season duration, cover, height, and the aboveground biomass of the community vegetation. However, the structural equation model revealed that the effect of phenology changes on the aboveground net primary production shifts was divergent among graminoid, weeds, and community. Our results shed light on the drought tolerance mechanisms of diverse vegetation groups at different drought timings. Thus, the drought timing should not be neglected in climate change studies, especially in research related to climate extremes.