Interfacial microbial communities drive litter decomposition along elevation gradients in alpine forest ecosystems

Litter decomposition is a key process in the global carbon cycle, primarily driven by microbial communities. At the litter-soil interface, microbes interact directly with both substrates and environmental conditions, often exhibiting distinct functional traits. However, differences between interface and non-interface microbial communities remain underexplored. This study conducted a year-long field litter burial experiment on Segrila Mountain in Tibet (3500–4300 m), using high-throughput sequencing and bioinformatics to investigate how interface microbes influence decomposition in alpine forests. Our findings reveal that, although the dominant bacterial and fungal phyla are similar between interface and non-interface soils, Acidobacteria are less abundant at the interface compared to non-interface soils, whereas Proteobacteria and Actinobacteria are more abundant. Interface microbial networks, constructed by Spearman correlations and modularity detection algorithms, display greater structural dynamics and complexity than those in non-interface soils. Variation partitioning analysis reveals that core microbial modules of the interface and non-interface soils, as well as elevation, account for 32.84 %, 3.79 %, and 5.39 % of the variation in litter decomposition, respectively. In the structural equation model, core interface microbial modules exert a significant and direct positive effect on both litter decomposition and lignocellulosic component breakdown, while non-interface modules are not significantly associated. Overall, the structure and activity of interface microbial communities dominate litter degradation dynamics. This study advances our understanding of the critical litter-soil interface processes in maintaining forest soil functions and offers a basis for managing carbon and nutrient dynamics under changing climate conditions in alpine forest ecosystems.