Land use change regulates soil microbial biodiversity-multifunctionality relationships by modulating soil moisture

Land use changes pose a severe threat to the structure and function of ecosystems. However, how these changes reshape soil microbial communities, ecosystem functions, and the biodiversity-multifunctionality (BEF) relationship remains unclear. Here, we investigated the diversity of soil microbial functional groups and multifunctionality across different land use types in the riparian zones of the Hailar River Basin, and assessed the influence of environmental changes on the microbial BEF relationship. It was found that land use change significantly altered soil physicochemical properties and microbial diversity. In human-dominated land use systems, soil moisture (SM) was markedly reduced, and the diversity of saprotroph fungi and arbuscular mycorrhizal fungi (AMF) was significantly decreased. SM was a key factor affecting soil multifunctionality and the microbial BEF relationships, and exhibited a threshold effect at a SM level of 0.25. Above the threshold (high SM conditions), the richness of bacteria and fungi was positively correlated with soil multifunctionality. Below the threshold (low SM conditions), the effect of fungal diversity on soil multifunctionality was enhanced, while that of bacterial diversity was diminished. Furthermore, the relationship between microbial functional group β-diversity and soil β-multifunctionality decoupled in low SM conditions. These findings highlight the necessity of maintaining SM and conserving soil microbial diversity for mitigating the decline in soil multifunctionality under land use changes.