Distinct Community Assembly and Co-Existence of Arbuscular Mycorrhizal Fungi and Diazotrophs Across Large-Scale Soil Fertility to Improve Functions in Alfalfa Cultivation Systems

Unravelling the community assembly processes of arbuscular mycorrhizal fungi (AMF) and diazotrophs as well as their co-existence under different soil fertility environments are vital to develop a better understanding of agroecosystem functions, which is a crucial yet poorly understood topic. We examined the soils from 99 typical alfalfa cultivation systems to formulate a comprehensive picture of AMF and diazotrophic community and presented the first simultaneous investigation of the assembly processes and their co-existence. The distributions of both AMF and diazotrophic communities were significantly (p < 0.05) corresponded to soil integrated fertility index (IFI). We quantified the relative contributions of five ecological processes in AMF and diazotrophic community assembly under different soil fertility environments, with stochastic assembly primarily determined across all soil fertility groups. The coexistence networks of AMF and diazotrophs were also notably different among typical soil fertility systems, where the most complex interactions were observed in high fertility system while medium fertility system was found to be the simplest. The active hubs detected in different fertility system were sensitively responded to different soil variables. We offered new opportunities to improve agroecosystem functions, especially for legumes, by regulating the potential key species or indirectly manipulating their drivers.