Arbuscular mycorrhizal symbiosis enhances microbial contribution to mineral-associated organic carbon persistence in the soil: Insights from soil microbial community and microbial necromass carbon

Abstract

The formation of mineral-associated organic carbon (MAOC), a critical soil fraction related to soil organic carbon (SOC) sequestration, is significantly influenced by microbial processes. Yet, how arbuscular mycorrhizal (AM) symbiosis impacts MAOC accumulation in rhizosphere soils through its effects on microbial contribution remains poorly understood. Here, we assessed the microbial community of different soil samples using 16S rRNA sequencing and found that AM symbiosis influenced the soil microbial community composition and enhanced soil microbial community functions related to carbon (C) degradation. The numbers of live and dead cells (all cells in the soil) were highest in AM-RS (rhizosphere soils in the AMF treatment) based on confocal laser scanning microscopy (CLSM) images. Meanwhile, AM symbiosis increased the proportions of apoptotic cells (19.02%) and necrotic cells (12.12%) in rhizosphere soils. Using soil amino sugars as microbial biomarkers, the concentrations of bacterial necromass C (188.01 g kg-1 OC) and fungal necromass C (392.19 g kg-1 OC) were highest in the MAOC fraction in AM-RS. Additionally, the MAOC content (17.20 g kg-1 soil) and proportion (42.06%) were highest in AM-RS. This research illustrates two primary mechanisms by which AM symbiosis enhances MAOC accumulation: (1) by altering the microbial community composition and function related to C degradation; and (2) by promoting the input of microbial necromass C, especially fungal necromass C. This research broadens our horizons to understand the mechanism of microbial contribution to MAOC accumulation stimulated by AM symbiosis in rhizosphere soils and provides management practices for AMF application to SOC sequestration.