Distinct roles of bacteria and fungi in driving rhizosphere and bulk soil multifunctionality of Abies georgei in an alpine forest

BACKGROUND: Root activity creates a unique microbial hotspot in the rhizosphere, profoundly regulating soil activity and associated soil multifunctionality (SMF), the ability of soil to deliver multiple functions or services simultaneously. However, empirical studies on the characteristics of SMF in the rhizosphere and bulk soil and their microbial regulatory mechanisms remain scarce. METHODS: To address this gap, we conducted a field sampling campaign in an alpine forest on the eastern Tibetan Plateau. Soil abiotic and biotic properties, including soil nutrient availability, enzyme activities and microbial attributes were examined to compare the characteristics of SMF in the rhizosphere and bulk soil of Abies georgei, and to explore how microbial mechanisms drive SMF in each compartment. RESULTS: We found that the rhizosphere consistently exhibited higher SMF than bulk soil, highlighting its enhanced functional potential regardless of environmental variation. The relationship between microbial diversity and SMF was compartment-specific: bacteria diversity was strongly associated with SMF in the rhizosphere, while fungal diversity was closely linked to SMF in the bulk soil. Furthermore, microbial biomass, particularly fungal biomass, had a strong influence on SMF in both rhizosphere and bulk soils. Structural equation modeling revealed that the relationship between soil diversity and SMF were primarily mediated by variations in soil abiotic properties, including soil pH in the bulk soil, and soil moisture and clay content in the rhizosphere. CONCLUSIONS: Our findings demonstrate that microbial contributions to soil multifunctionality are compartment-dependent and emphasize the need to integrate the rhizosphere perspective into biodiversity-multifunctionality frameworks for improving predictions of soil functions in terrestrial ecosystems.