Microbial functional potential and soil–atmosphere greenhouse gas fluxes across subtropical forest types

Forest soils play a critical role in the global carbon cycle, but the microbial and environmental factors underlying the heterogeneity of soil greenhouse gas exchange at the soil–atmosphere interface remain poorly understood. Focusing on broadleaf, coniferous, and bamboo forests, we integrated litter chemical and hydrological traits, soil physicochemical properties, metagenomics, and untargeted metabolomics to examine the associations of aboveground litter characteristics and belowground soil conditions with microbial functional potential, metabolite composition, and greenhouse gas fluxes. Our results showed that broadleaf litter had higher carbon/nitrogen ratios and lignin content, while broadleaf soils had lower bulk density and greater water-holding capacity, and exhibited significantly higher cumulative carbon dioxide efflux than coniferous and bamboo forests. Bamboo litter showed higher water absorption rates and greater potential water-holding and interception capacities, while bamboo soils were enriched in functional genes associated with plant-derived polysaccharide degradation and fermentation-related carbon transformations. Procrustes analysis further indicated coordinated variation between microbial functional potential and metabolite profiles. All three forest types acted as net methane (CH 4 ) sinks, with no significant differences in instantaneous CH 4 fluxes among forest types but significant differences in cumulative CH 4 uptake, which was highest in broadleaf forests. The intermediate microbial functional and metabolite profiles of coniferous soils further indicated that omics-level variation did not necessarily parallel environmental gradients across forest types. This study provides a more integrated understanding of soil–atmosphere carbon exchange across subtropical forest types and highlights the importance of jointly considering above- and belowground characteristics when evaluating forest soil carbon dynamics.