Environmental Heterogeneity and Host Genotype Jointly Shape Endophytic Bacterial Community Composition Associated with an Endemic Chinese Sphagnum Species

Peat mosses of the genus Sphagnum are keystone species in peatland ecosystems and play critical roles in carbon sequestration, nitrogen fixation, and hydrological regulation. Indeed, these ecological functions are largely mediated by endophytic bacteria associated with Sphagnum. Here, five populations of the endemic Chinese moss species, S. multifibrosum, were sampled across southern China in peatland (PH) and rock habitats (RH). High-throughput sequencing of 16S rRNA and nitrogenase (nifH) genes was applied to characterize overall endophytic bacterial diversity and diazotroph diversity associated with S. multifibrosum, respectively, alongside host microsatellite genotyping. Proteobacteria was the dominant endophytic bacterial phylum. The bacterial communities exhibited significant spatial separation between eastern and western communities and community dissimilarities significantly increased with increasing geographic distances. Environmental heterogeneity and host genetics jointly shaped endophytic bacterial community assemblage. Climate was the most important determinant influencing bacterial composition, followed by host genotype and habitat type. Temperature, precipitation, and nitrogen deposition were the primary environmental factors that influenced composition. Bacterial diversity and composition exhibited no statistically significant differences between the two habitats. Further, the richness and abundances of diazotrophs and methanotrophs from PH communities were higher than in RH communities. Co-occurrence network analysis suggested that RH bacterial networks had lower connectance but were more modularized and exhibited higher complexity than PH networks. These results highlight the ecological functions of peat mosses in carbon and nitrogen cycling and suggest a need to prioritize the conservation of S. multifibrosum in peatland environments under global climate change. The results also provide a framework to help future wetland management and biodiversity conservation efforts in China.