Tree species composition alters the decomposition of mixed litter and the associated microbial community composition and function in subtropical plantations in China

Converting coniferous plantations to mixed plantations influences the microbial community composition and potential functions during litter decomposition. However, it is unclear how litter decomposition and associated microbial communities are interactively affected by litter mixing and environmental factors. Here, an in situ litter decomposition experiment was conducted to investigate the dynamics of microbial diversity in mixed litter (at a mass ratio of 1:1) from coniferous (Pinus massoniana) and broadleaf tree, including Bretschneidera sinensis, Manglietia chingii, Cercidiphyllum japonicum, Michelia maudiae, and Camellia oleifera. We found that the mass loss from mixed litter was higher than that of monospecific litter. The chemical characteristics of the broadleaf tree species included in the mixed litter significantly affected the microbial community composition and diversity, and those effects increased over time. Compared to the monospecific litter, the mixed litter had a higher relative abundance of saprotrophs and microbial functional groups related to carbon and nitrogen cycling. Moreover, litter chemistry (i.e., pH, lignin and cellulose content) and environmental factors (i.e., air temperature and soil moisture content) were the most crucial factors affecting the microbial decomposer community. Our results suggest that introducing broadleaf tree species with high litter quality to coniferous plantations changes the composition and function of microbial communities related to litter decomposition, which is conducive to accelerating litter decomposition in subtropical plantations.