Moss-microbe interactions play important roles for ecosystem processes in boreal forests. Yet, the extent to which the environment and host-specific characteristics drive the composition and metabolic potential of boreal moss microbiomes is still poorly understood. In this study, we use shotgun metagenomics to identify the taxonomy and metabolic potential of the bacterial communities of four moss species in the boreal forests of Northern Québec, Canada. To better characterize moss bacterial community composition and diversity, we assembled the genomes of 110 potentially novel bacterial species. Our results highlight that moss genus, species, gametophyte section, and key abiotic factors drive moss-associated bacterial community composition and diversity. Green gametophyte sections harbored differentially abundant bacteria (e.g., Bradyrhizobia) exhibiting significant carbon fixation capacities, particularly through the phosphate acetyltransferase-acetate kinase pathway. On the other hand, brown gametophyte sections harbored differentially abundant Cyanobacteria (e.g., Stigonema spp.) demonstrating partial pathways for anoxygenic photosynthesis and nitrogen fixation, which are important for nitrogen cycling in boreal ecosystems. Overall, our findings provide insights into the relationships between boreal mosses and their bacterial communities, for which data remains scarce. As global change accelerates in boreal ecosystems, identifying the roles of moss microbial symbionts in influencing their hosts and ecosystem functions becomes critical.
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