Ectomycorrhizal exploration types mediate soil decomposition and nitrogen dynamics of sub-alpine forest

Background and Aims Ectomycorrhizal (ECM) fungi interact with saprotrophic fungi and bacteria, thereby influencing soil decomposition and nitrogen (N) mineralization. However, how the functional composition of ECM communities (i.e., exploration types) affects these processes under varying levels of N availability remains unclear. Methods We conducted a soil trenching experiment to manipulate root-associated fungal communities in two forest types—natural forest (higher N availability, dominated by long- and medium-distance ECM types) and plantation (lower N availability, dominated by contact exploration types). We evaluated the effects of trenching on fungal biomass, community composition, soil enzyme activities, nitrogen mineralization, and root decomposition. Results Trenching significantly reduced ECM fungal biomass and the relative abundance of medium-distance exploration types, particularly in the natural forest. In contrast, saprotrophic fungal sequence read abundance increased more in the plantation. Enzyme activities (except β-glucosidase) and nitrification rates were more strongly affected by trenching in the natural forest, where nitrification was positively correlated with the activities of leucine aminopeptidase and N-acetyl-β-D-glucosaminidase, and negatively correlated with ECM fungal biomass. Root decomposition increased only in the plantation and was also negatively correlated with ECM fungal biomass. Conclusion ECM exploration types influence soil N cycling and decomposition through their effects on fungal biomass and enzyme activity, with these impacts modulated by soil N availability. In low-N soils dominated by contact exploration type-ECM fungi, ECM communities exert a suppressive effect on decomposition. These findings underscore the role of ECM functional traits in shaping belowground processes under changing forest conditions.