Revealing the transfer pathways of cyanobacterial-fixed N into the boreal forest through the feather-moss microbiome.

Introduction: 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.

Methods: 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.

Results: NanoSIMS images reveal that newly fixed N, derived from cyanobacteria, is incorporated into moss tissues and associated bacteria, fungi and micro-algae.

Discussion: 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.