The functional role of arbuscular mycorrhizal fungi in enhancing soil organic carbon stocks and stability in dryland

Abstract

Arbuscular mycorrhizal fungi (AMF) are known to influence soil organic carbon (SOC) stock, but the mechanisms by which they affect SOC stability in the rhizosphere remains poorly understood. To address this gap, a 7-year field observation was conducted in a rainfed dryland maize field, with AMF inoculation, AMF exclusion (only benomyl treatment), and the control (no AMF and no benomyl). AMF introduction increased soil occluded particulate organic carbon (oPOC) and mineral-associated organic carbon (MAOC) contents by 15.6 % and 7.1 %, respectively, compared to the control. However, no significant changes were observed in free particulate organic carbon (fPOC) levels. As expected, AMF exclusion led to a general reduction in SOC content. Analyses of in situ13C labeling showed that AMF inoculation evidently promoted the retention of 13C in oPOC (13.6 %) and MAOC (5.4 %), thereby enhancing SOC stability. High-throughput sequencing results revealed that AMF inoculation led to significant increases in the diversity and abundance of rhizosphere fungal community, with higher co-occurrence network complexity. Meanwhile, the diversity and abundance of rhizosphere bacterial community were substantially reduced (p < 0.05). Importantly, long-term AMF inoculation was observed to weaken soil N stocks, and inhibit microbial hydrolase secretion for C sources. The findings suggest that AMF inoculation can conserve and stabilize SOC by enhancing fungal community proliferation, while reducing microbial extracellular enzyme activity through soil N depletion. Therefore, AMF can be considered rhizosphere carbon engineer that boost persistent carbon sink in drylands via selectively affecting SOC components. The findings provide new insights into global nature-based carbon neutrality strategies.