Dominant plant functional groups outperform diversity in regulating biomass under yak seasonal grazing in an alpine meadow on Qinghai-Tibetan Plateau.

Seasonal grazing is a practice for alpine meadows that involves rotating pastures with the seasons. Nevertheless, the mechanisms by which seasonal grazing affects the aboveground biomass (AGB) of plant communities and functional groups in the alpine meadows of the Qinghai-Tibetan Plateau remain unclear. Based on a long-term seasonal grazing management experiment established in an alpine meadow since 2010, this study investigated the effects of spring, summer, autumn, and winter grazing on plant diversity, functional group species richness, climate, soil nutrients, and soil enzyme activity in alpine meadows. We assessed plant diversity, functional group species richness, soil properties, and soil enzyme activity to explore potential mechanisms underlying seasonal grazing effects on community AGB and functional group AGB. The results indicated that winter grazing leads to higher AGB in the plant community, Gramineae, and Cyperaceae, whereas summer grazing reduces plant AGB. Furthermore, functional group species richness plays a more critical role than plant diversity in regulating plant AGB. Plant diversity and soil properties are key mediators of grazing effects on plant AGB, and they have a significant positive impact on both plant community and functional group AGB. In different grazing seasons, alpine meadow plant AGB shows strong sensitivity to climate (precipitation and temperature). Summer and autumn grazing enhance plant diversity, while winter grazing promotes the accumulation of plant AGB. Therefore, moderate grazing during the periodic cold and warm seasons is an appropriate grazing system for maintaining the sustainable development of alpine meadows.