Litter decomposition regulated by stand ECM dominance but not litter mycorrhizal type in a subtropical mountainous forest

Litter decomposition is a key process regulating terrestrial carbon and nutrient cycling. Tree mycorrhizal association shape both litter chemistry and below-ground ecological processes. However, how mycorrhizal association mediates litter decomposition is poorly understood, particularly in species-rich subtropical forests. Here, we conducted two in-situ litter decomposition experiments to disentangle the effects of mycorrhizal type and stand ECM dominance on litter decomposition. One-year field litter decomposition experiment of 21 AM and 6 ECM tree species indicated that AM litter decomposed faster than ECM litter only during the initial one month, but this difference diminished over time. The overall decomposition rates of AM and ECM litter were comparable for the entire year. Litter nutrient concentrations were the main factors affecting litter decomposition. In the initial one month, leaf dry matter content (LDMC) was the most important factor. AM and ECM litter decomposition in plots with a natural gradient of ECM tree dominance showed that the decomposition rates of both AM litter and ECM litter decreased significantly in plots with increasing ECM dominance. Stand-level variation in decomposition was strongly associated with reductions in soil nitrogen availability, increased fine root biomass, and decreased abundance of saprotrophic fungi, suggesting intensified competition between ECM and saprotrophic fungi under N-limited conditions suppressed litter decay.Our findings underscore stand level ECM dominance, rather than litter mycorrhizal type alone, plays a key role in regulating litter decomposition. This suggest that shifts in mycorrhizal dominance may have far-reaching consequences for carbon and nutrient cycling in subtropical forests.