Nitrogen deposition homogenizes moss-microbiomes and associated nitrogen fixation but with host-specific responses.

Moss microbiomes contribute significantly to terrestrial nitrogen (N) cycling through N fixation, especially in nutrient-poor environments. Yet, the relative roles of environment (abiotic factors) and host species (biotic factors) in shaping these microbiomes remain understudied even though this could reveal how host-specific moss-associated microbiomes are. To assess whether moss-associated microbiomes are shaped predominantly by the moss host or by the environment, we compared three common moss species ( IMPORTANCE: Mosses host diverse microbiomes that contribute to terrestrial N cycling through processes such as nitrogen (N) fixation. Thus, these microbial communities play important roles in nutrient-poor environments where mosses often dominate. Here, N fixation is a key source of N input, making it important to understand what drives microbiome composition and associated N fixation activity. We ascertained the roles of the environment and moss-host species in shaping the moss-microbiomes and associated N fixation rates in two forest types with varying N deposition rates. We showed that forest type shapes moss-associated microbiomes and N fixation activity, while aligning N availability also aligned N fixation activity and changed the moss microbiomes with implications for the ecosystem functions they provide.