Host plant and soil nutrient filters mediate long-term grazing on arbuscular mycorrhizal fungi in desert grasslands.

Arbuscular mycorrhizal fungi (AMF) enhance plant performance through improved nutrient acquisition, stress resilience, and pathogen resistance while strengthening ecosystem functions through soil structure stabilization and carbon sequestration. Livestock grazing is the dominant grassland land-use globally, but the effects of increased grazing intensity on AMF remain debated. Importantly, the mechanistic drivers of AMF responses to grazing intensity remain poorly understood, particularly in arid grasslands. Based on an 18-yr experiment with four grazing intensities (no grazing, light grazing, moderate grazing, and heavy grazing) in a desert grassland in Inner Mongolia, we examined the response of the AMF community to grazing and the mechanisms underlying the observed changes in AMF communities. AMF diversity, as well as the number of nodes, edges, and overall complexity of the AMF inter-species network, decreased progressively from no grazing to heavy grazing. Grazing also altered AMF community composition, with a significant increase in the abundance of the genus Glomus under heavy grazing. These changes in AMF communities were dominated by deterministic processes. Specifically, intensifying grazing is accompanied by reduced plant diversity and soil nutrient availability, as well as the prevalence of more stress-tolerant plant ecological strategies, all of which contribute to the simplification of AMF communities. Our results demonstrate that both host plants and soil nutrient availability are the key drivers shaping AMF communities in grazed desert grasslands. Given the important functions of AMF and the negative impacts of long-term grazing on it, there is an urgency to promote diverse grazing systems and reduce grazing pressure to improve grassland management.