Grazing increases the complexity of networks and ecological stochastic processes of mycorrhizal fungi

Arbuscular mycorrhizal fungi (AMF) form extensive symbiotic relationships with plants, which are critical for plant-driven biogeochemical cycles and ecosystem functions. Grazing and mowing, which are common grassland utilization patterns globally, significantly alter plant community characteristics as well as soil nutrients and structure, thereby potentially influencing AMF communities. However, the effects of these grassland managements on AMF community structure and ecological processes remain unclear. Here, we investigated AMF communities in cattle grazing, sheep grazing, and mowing grasslands. We examined AMF community diversity, composition, assembly processes, and network interactions. Our results revealed distinct AMF compositions across different grassland managements. In cattle and sheep grazing grasslands, the AMF community assembly processes were determined by dispersal limitation and drift, with increased importance of stochasticity. Although AMF abundance did not alter by grassland managements, AMF diversity decreased under sheep grazing, associated with reduced pH levels compared to cattle grazing or mowing. AMF formed more complex (higher average degree and graph density) and integrated (lower modularity) networks in grazing grasslands than mowing grasslands. The AMF network in cattle grazing grasslands showed the highest stability, associated with a broader habitat niche, balanced interspecies competition, and higher soil AP and MBN. Meanwhile, some species with high adaptability to grazing became key nodes in the AMF network, such as Funneliformis. Our findings highlight significant AMF responses to grazing, including increased network complexity and ecological stochasticity, providing new insights into how grassland managements influence the composition and assembly patterns of soil symbiotic microbial communities.