Grazing intensity shapes soil fungal diversity and co-occurrence networks across soil depths

Grazing is an important disturbance affecting grassland ecosystems in agro-pastoral ecotones, yet its effects on soil fungal diversity and co-occurrence networks across vertical soil profiles remain unclear. We selected a typical grassland at the junction of the Loess Plateau and the Mongolian Plateau in northern China and established four grazing intensities: ungrazed control (CK), light grazing (LG), moderate grazing (MG), and heavy grazing (HG). Soil samples were collected from three layers (0–2, 2–10, and 10–20 cm). Soil physicochemical properties, high-throughput sequencing, co-occurrence network analysis, and structural equation modeling (SEM) were used to examine fungal community responses and their potential associated pathways. Grazing intensity and soil depth significantly influenced soil physicochemical properties and fungal community composition. Fungal α-diversity exhibited soil layer-dependent responses to grazing intensity, with light and moderate grazing maintaining higher fungal richness in surface soils than heavy grazing, whereas fungal richness responses differed among deeper soil layers. Factorial PERMANOVA showed significant effects of grazing intensity ( R 2 = 0.145, P = 0.043) and soil depth ( R 2 = 0.151, P < 0.001) on fungal community composition, whereas their interaction was not significant. Co-occurrence network analysis revealed variation in fungal network organization among grazing intensities, with moderate grazing associated with higher network connectivity and heavy grazing associated with higher network modularity. Piecewise structural equation modeling further indicated indirect associations between grazing intensity and fungal diversity involving vegetation biomass, soil resources, soil pH, and microbial biomass. Overall, our findings demonstrate that grazing effects on soil fungal communities are strongly soil layer-dependent and are shaped by interactions among plant inputs, soil environmental conditions, and microbial processes. This study provides insights into the ecological consequences of grazing intensity and the mechanisms underlying fungal community responses in agro-pastoral ecotone grasslands.