Arbuscular mycorrhizal fungi outcompete fine roots in determining soil multifunctionality and microbial diversity in a desert ecosystem

Fine roots and mycorrhizal fungi play a crucial role in soil nutrient cycling and microbial processes. However, the importance of the symbioses between fine roots and arbuscular mycorrhizal fungi (AMF) in different plant functional groups to maintain soil multifunctionality (the ability to provide multiple functions and services) and microbial diversity remains unclear, especially in desert ecosystems. In this study, we conducted an ingrowth core experiment on three vegetation types, namely shrub-dominated, grass-dominated, and mixed vegetation communities, in the Mu Us Desert, northern China, to investigate the importance of fine roots and mycorrhizal fungi in shaping soil nutrient composition and microbiome. Furthermore, we detected the relationships among AMF-related inputs [extraradical AMF hyphae and glomalin-related soil protein (GRSP)], soil multifunctionality, and soil microbial diversity. We found that most of the soil properties associated with nutrient cycling and microbial community composition and diversity varied among the three vegetation types, but were not significantly different between distinct ingrowth core treatments with fine root and hyphal access. AMF-related inputs, especially the easily extractable GRSP, were the most important determinants of soil multifunctionality and microbial community diversity across the shrub and grass communities, while the changes in soil multifunctionality and microbial diversity were inconsistent with the trend of fine root biomass. Moreover, AMF-related inputs were positively correlated with soil nutrients, particularly soil organic carbon (SOC). In contrast to the minimal negative correlation between SOC and soil microbial richness, soil multifunctionality was positively correlated with SOC. These findings support the role of AMF in shaping soil multifunctionality and microbial diversity by stabilizing SOC in a desert ecosystem, regardless of the fine root accessibility of plant functional groups. Therefore, this study improved our understanding of plant-derived carbon in the soil and its effects on the induction of soil abiotic and biotic processes in resource-limited ecosystems.