Advanced leaf emergence partially mitigated the negative effect of plant size on biomass under warming

Understanding the mechanisms that maintain the productivity of grassland communities is crucial for ecosystems to provide functions and services under climate change and for developing grassland management and restoration strategies. Plant traits, such as phenological (timing) and morphological (size) traits, are essential for predicting ecosystem function under climate change. However, how plant traits respond to warming and precipitation change and their combined consequences on ecosystem function (e.g., biomass) remain poorly understood. Here, we conducted a 5‐year field warming and precipitation change experiment in an alpine meadow on the Tibetan Plateau, and measured six plant phenological and morphological traits of 10 common species to research how functional traits regulate plant biomass under warming and precipitation change. Warming rather than precipitation advanced plant leaf emergence and lengthened the growing season and reduced mean plant height for sedges and forbs, while it reduced leaf area of sedges and grasses. Moreover, the negative effects of warming‐induced reductions in plant height and leaf area on sedge biomass were offset by the positive effects of advanced leaf emergence, which did not completely mitigate the negative effects of low plant height on forb biomass production. Our results suggest that the negative effect of warming on the biomass of sedges and forbs through reduced plant size will be partially mitigated by the compensatory effect of advanced leaf emergence. This finding further emphasizes that the crucial and opposing roles of phenological and morphological traits should be considered when assessing biomass production and sustainable services in alpine grasslands under climate change.