Research advances in the impacts of ectomycorrhizal fungi on the formation and decomposition of soil organic matter in forests.

Ectomycorrhizal (EcM) fungi are one of the important functional groups of soil fungi, playing a crucial role in the formation, stabilization, and decomposition of soil organic matter (SOM). We summarized the main processes and mechanisms by which EcM fungi contribute to SOM formation, stabilization, and decomposition in forests. Plants allocate a portion of photosynthetic products to symbiotic EcM fungi, which participate in SOM formation by importing them into the soil in the form of mycorrhizal exudates or necromass, whose activities promote the formation of soil aggregate structure and SOM stabilization. EcM fungi decompose SOM directly by secreting extracellular enzymes or by driving the Fenton reaction to generate hydroxyl radicals. They also influence SOM decomposition indirectly by enhancing the activity of saprotrophic fungi (priming effect) or inhibiting their activity (Gadgil effect). The precise quantification of EcM fungi's role in SOM formation remains unclear. Most available studies are concentrated in Europe and North America, but the difference in methodologies makes it difficult to integrate data across regions. Future research should adopt standardized techniques and promote cross-regional collaborative studies. Current understanding of EcM fungi's role in SOM decomposition is mainly based on a few laboratory-cultured species. Future studies should include a broader range of EcM fungal species and investigate their roles in natural environments, particularly in different soil types and forest communities. In addition, the interactions between EcM fungi and saprotrophic fungi have significant impacts on SOM dynamics. Future research should explore the responses of EcM fungi to climate, soil and vegetation in depth to better understand their role in soil carbon cycling.