Grazing does not influence soil arbuscular mycorrhizal fungal diversity, but increases their interaction complexity with plants in dry grasslands on the Tibetan Plateau

Animal grazing substantially influences soil arbuscular mycorrhizal fungi (AMF) and plants, however, its effects on soil AMF-plant interactions are still not clearly defined. This is particularly concerned in dry grasslands where plant growths are more dependent on soil AMF to tolerate environmental stresses. In these regions, animal grazing has been rapidly increasing and degrading grasslands, e.g. the Tibetan Plateau. To reveal the AMF-plant interactions and their responses to grazing, we investigated the soil AMF-plant interaction and AMF community assembly processes in paired fields of grazed and non-grazed grasslands using Illumina sequencing on the Tibetan Plateau. Our results demonstrated that grazing did not influence the soil AMF diversity and community structure, but substantially altered AMF-plant interaction and AMF community assembly processes. Network analysis demonstrated that grazing enhanced AMF-plant interaction complexity, indicated by the increased network connectance, average clustering coefficient and importance of hub plants in grazed grasslands. Additionally, grazing substantially increased the stochasticity of AMF community assembly in steppe and desert soils by reducing the deterministic effects of plant richness and enhancing AMF-plant interaction. Soil AMF richness positively correlated with plant evenness in non-grazed grasslands (P < 0.05), but such correlations diminished in grazed grasslands. Our findings indicate that AMF-plant interaction and AMF community assembly are more sensitive than AMF diversity and community structure to grazing. Therefore, animal grazing could profoundly interrupt ecosystem functions driven by soil AMF-plant interaction before the diversity loss.