Soil Organic Matter Dynamics Mediated by Arbuscular Mycorrhizal Fungi - an Updated Conceptual Framework

Arbuscular mycorrhizal (AM) fungi play an important role in soil organic matter (SOM) formation and stabilization. Previous studies have emphasized organic compounds produced by AM fungi as persistent binding agents for aggregate formation and SOM storage. This concept overlooks the multiple biogeochemical processes mediated by AM fungal activities, which drive SOM generation, reprocessing, reorganization, and stabilization. Here, we propose an updated conceptual framework to facilitate a mechanistic understanding of the role of AM fungi in SOM dynamics. In this framework, four pathways for AM fungi-mediated SOM dynamics are included: 'Generating', AM fungal exudates and biomass serve as key sources of SOM chemodiversity; 'Reprocessing', hyphosphere microorganisms drive SOM decomposition and resynthesis; 'Reorganizing', AM fungi mediate soil physical changes and influence SOM transport, redistribution, transformation, and storage; and 'Stabilizing', AM fungi drive mineral weathering and organo-mineral interactions for SOM stabilization. Moreover, we discuss the AM fungal role in SOM dynamics at different scales, especially when translating results from small scales to complex larger scales. We believe that working with this conceptual framework can allow a better understanding of AM fungal role in SOM dynamics, therefore facilitating the development of mycorrhiza-based technologies toward soil health and global change mitigation.