Arbuscular mycorrhizal symbiosis increases microbial contribution to mineral-associated organic carbon accumulation in rhizosphere soils: insights from soil microbial community and microbial necromass C

The formation of mineral-associated organic carbon (MAOC), a critical soil fraction related to soil organic carbon (SOC) sequestration, is significantly influenced by soil microbial physiological traits. Yet, How AM symbiosis affects MAOC accumulation in rhizosphere soils by influencing soil microbial activities and products remains poorly understood. Here, utilizing 16S rRNA sequencing, we explored soil microbial community composition and function in different soil samples. Importantly, AM symbiosis enhanced soil microbial community functions related to C degradation, which promoted the proportion of MAOC in rhizosphere soils by decomposing particular organic carbon (POC). The numbers of live cells and dead cells were highest in AM-RS based on confocal laser scanning microscopy (CLSM) images. Meanwhile, AM symbiosis increased the proportion of apoptotic cells (19.02%) and necrotic cells (12.12%) in rhizosphere soils. Using soil amino sugars as microbial biomarkers, the contents of bacterial necromass C (188.01 g kg OC-1) and fungal necromass C (392.19 g kg OC-1) were determined and presented highest in MAOC fraction in AM-RS. Additionally, MAOC content (17.20 g kg soil-1) and proportion (42.06%) were highest in AM-RS. Our study illustrates two main ways in which AM symbiosis enhances MAOC accumulation: (1) aggravating the decomposition of root exudate-derived POC and increasing MAOC proportion; (2) promoting microbial turnover and microbial necrotic C input, 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.