Grazing by Tibetan Sheep Enhances Soil Bacterial and Fungal Diversity in Cold Season Pastures of Alpine Meadows on the Northern Qinghai–Tibetan Plateau

Grazing management methods are of great significance to the health of alpine meadow soil in the Qinghai–Tibet Plateau and the sustainable use of grassland. Soil microbes are important indicators of soil health. We designed this experiment to clarify the relationship between grazing management practices and soil microorganisms. We investigated the effects of grazing Tibetan sheep, grazing Tibetan sheep + yak, and grazing yak on the soil microbial composition and microbial structure by measuring the physical properties, chemical properties, and enzyme activities of soils in Tianzhu County, Gansu Province. The results showed that grazing by different livestock changes the structure of bacterial and fungal communities in the soil. In particular, Actinobacteria constituted the highest proportion of bacterial community among the grazing modes. The proportion of Ascomycota was the highest in the fungal community. Grazing by Tibetan sheep significantly increased the bacterial community diversity in the soil, with Shannon and Chao indices showing respective increases of 1.23% and 5.10% compared with the sample grazed by Tibetan sheep + yaks. Grazing by Tibetan sheep + yak significantly increased the Shannon index of the fungal community. Both correlation and structural equation modeling analyses indicated that the bacterial community diversity was influenced by soil enzyme activity, whereas the fungal community diversity was influenced by a combination of enzyme activity and physical properties. Overall, Tibetan sheep grazing was found to be more conducive to the healthy development of soil and the sustainable utilization of alpine meadows on the Qinghai–Tibet Plateau.