Research progress in soil organic carbon stabilization mediated by arbuscular mycorrhizal fungi

Soil organic carbon (SOC) stabilization is a critical process in terrestrial organic carbon dynamics and is important in maintaining soil fertility and reducing greenhouse gas emissions. Traditionally, the stable carbon pool was thought to be dominated by the physico-chemical protection of certain recalcitrant organic compounds and the formation of recalcitrant humic substances. However, recent studies have suggested that microbe-mediated carbon cycling plays an important role in soil organic carbon stabilization. Arbuscular mycorrhizal fungi (AMF), as one of the most important symbiotic fungi in soil, contribute predominantly to transportation and distribution of plant photosynthetic carbon into the soil, which influence the terrestrial carbon cycling. However, the potential of AMF in SOC stabilization has not been fully explored. Thus, on the basis of estimating the allocation of plant photosynthetic carbon to extraradical hyphae, we reviewed the possible mechanism of AMF promoting the formation of soil stable organic carbon, mainly including the carbon retention in living hyphae, resistance and soil mineral adsorption of exudates and necromass, improvement of the quality and quantity of plant-derived carbon, priming effect of secretions and necromass and stabilization of soil aggregate. Then we reviewed the abiotic (climate, soil nutrition and minerals) and biotic (plant and AMF species) factors influencing the carbon stabilization. Finally, the future research directions of the interaction mechanism between AMF and SOC turnover were proposed, including exploring the mechanism of transformation of photosynthetic carbon into stable SOC in mycorrhizal plants, analyzing the contribution of AMF to stable SOC in different ecosystems and the influencing factors, and clarifying the relationships among AMF biomass, diversity and stable SOC under different management practices. These discussions provide a theoretical basis for fully utilizing AMF to enhance the carbon sink in terrestrial ecosystems and mitigating climate change.