Fungal diversity shapes ecosystem multifunctionality in alpine grasslands under different herbivore assemblages: A case study from the Qinghai-Tibetan Plateau

Ecosystem multifunctionality, defined as the capacity of ecosystems to simultaneously sustain multiple functions and services, is a key indicator of ecological sustainability. Grazing represents the primary land-use practice in the alpine grasslands of the Qinghai-Tibetan Plateau; however, the effects of different herbivore assemblages on ecosystem multifunctionality remain insufficiently understood. In this study, we conducted a series of precisely controlled grazing experiments to assess the effects of different herbivore assemblages—yak-only, Tibetan sheep-only, and mixed yak–sheep grazing at varying ratios—on ecosystem multifunctionality in alpine grasslands. Our results demonstrate that, compared with fenced controls, moderate-intensity mixed grazing significantly enhanced ecosystem multifunctionality, with the greatest improvement observed at a yak-to-sheep ratio of 1:2 (+22.63 %). Key drivers of multifunctionality included plant, bacterial, and fungal Shannon diversity, fungal β-diversity, and soil properties such as total nitrogen, total phosphorus, and bulk density. Notably, grazing primarily promoted multifunctionality indirectly by enhancing fungal community diversity, which accounted for 39.53 % of the observed variation. These findings suggest that optimizing grazing strategies—particularly implementing mixed yak–sheep grazing at a 1:2 ratio under moderate intensity—can effectively balance ecological and economic objectives, supporting the sustainable development and adaptive management of alpine grassland ecosystems.