Biological N fixation in feather-mosses is one of the largest inputs of new nitrogen (N) to boreal forest ecosystems; however, revealing the fate of newly fixed N within the bryosphere (i.e. bryophytes and their associated organisms) remains uncertain. Herein, we combined N tracers, high resolution secondary ion mass-spectrometry (NanoSIMS) and a molecular survey of bacterial, fungal and diazotrophic communities, to determine the origin and transfer pathways of newly fixed N within feather-moss ( ) and its associated microbiome. NanoSIMS images reveal that newly fixed N , derived from cyanobacteria, is incorporated into moss tissues and associated bacteria, fungi and micro-algae. These images demonstrate that previous assumptions that newly fixed N is sequestered into moss tissue and only released by decomposition are not correct. We provide the first empirical evidence of new pathways for N fixed in feather-mosses to enter the boreal forest ecosystem (i.e. through its microbiome) and discuss the implications for wider ecosystem function. [Abstract copyright: Copyright © 2022 Arróniz-Crespo, Bougoure, Murphy, Cutler, Souza-Egipsy, Chaput, Jones, Ostle, Wade, Clode and DeLuca.]