Asynchronous phenological responses to warming affect biomass production contrastingly in flowering functional groups

Earlier spring vegetation growth under warming can either enhance summer height growth by increasing carbon sequestration potential or impair it by consuming additional resources needed for subsequent growth. However, the underlying mechanism and its temporal variations remain unclear. Based on a 7‐year field experiment with warming and altered precipitation in an alpine meadow on the eastern Tibetan Plateau, we examined their effects on leaf emergence and reproductive phenology, plant height at different phenological stages, height growth rate and biomass production between flowering functional groups (FFGs) from 2021 to 2023. We found that warming differentially affected the height growth rates of alpine plants during their reproductive stages between FFGs and that asynchronous responses of reproductive phenology to warming further mediated warming effects on biomass production. Specifically, for early‐spring flowering plants, warming advanced spring phenology and increased plant height growth rate between leaf emergence and flowering but constrained height growth rate in the later fruiting period, thereby reducing their biomass production. In contrast, for mid‐summer flowering plants, warming consistently advanced both vegetative and reproductive phenological events and promoted plant height growth rate throughout the growing season, ultimately increasing biomass production. Synthesis. These results emphasize the critical role of height growth rate and plant phenology in the biomass production of alpine plants under ongoing climate change. Our study additionally highlights the importance of understanding how plant functional groups govern responses to changing climate conditions, which is essential for forecasting phenological and community‐level changes.