The bacterial communities of Alaskan mosses and their contributions to N₂-fixation

Mosses in high-latitude ecosystems harbor diverse bacterial taxa, including N₂-fixers which are key contributors to nitrogen dynamics in these systems. Yet the relative importance of moss host species, and environmental factors, in structuring these microbial communities and their N₂-fixing potential remains unclear. We studied 26 boreal and tundra moss species across 24 sites in Alaska, USA, from 61 to 69° N. We used cultivation-independent approaches to characterize the variation in moss-associated bacterial communities as a function of host species identity and site characteristics. We also measured N₂-fixation rates via ¹⁵N₂ isotopic enrichment and identified potential N₂-fixing bacteria using available literature and genomic information.

Host species identity and host evolutionary history were both highly predictive of moss microbiome composition, highlighting strong phylogenetic coherence in these microbial communities. Although less important, light availability and temperature also influenced composition of the moss microbiome. Finally, we identified putative N₂-fixing bacteria specific to some moss hosts, including potential N₂-fixing bacteria outside well-studied cyanobacterial clades.

The strong effect of host identity on moss-associated bacterial communities demonstrates mosses' utility for understanding plant-microbe interactions in non-leguminous systems. Our work also highlights the likely importance of novel bacterial taxa to N₂-fixation in high-latitude ecosystems. Video Abstract.