Response of Soil Protist Community to Grazing Disturbance in an Alpine Grassland on the Eastern Qinghai–Tibet Plateau

Grazing disturbance strongly affects grassland ecosystem structure and function, but its impacts on soil protist communities across vertical soil profiles remain unclear in alpine grasslands. We investigated soil protist community composition, alpha diversity, and their relationships with environmental factors under four grazing intensities (no grazing, light, moderate, heavy grazing) at three depths (0–10, 10–20, 20–30 cm) on the eastern Qinghai–Tibet Plateau. Our results showed that grazing significantly altered the relative abundance of dominant protist orders, including Pyrenomonadales, Kinetoplastida, and Amoebida. The Shannon–Wiener and Pielou indices of protists decreased significantly with increasing soil depth, while grazing mainly reduced the Margalef index. Soil total nitrogen, bulk density, and pH were the dominant factors shaping soil protist community structure. Overall, soil protists were more sensitive to soil depth than grazing intensity. These findings improve our understanding of vertical protist distribution under grazing disturbance and provide a scientific basis for sustainable grassland management.