Assessment of moss-associated biological nitrogen fixation of dominant moss species in mature black spruce forests in Eastern Canada

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Biological nitrogen fixation (BNF) by bryophytes is an essential source of new nitrogen in nitrogen-limited boreal ecosystems. This assessment is, however, primarily based on reports from northern Europe and, to a lesser extent, Western North America. A more systematic and extensive evaluation of nitrogen fixation by moss is required to close current gaps in records of moss BNF and better assess the importance of bryophytes on N input in boreal ecosystems. Here, we evaluated nitrogen fixation activity and contribution to N input of dominant bryophyte species in black spruce forests from Eastern Canada. We assessed the relative abundance, BNF activity, and relative contribution to nitrogen input on five sites along a 600 km transect. We report that several moss species contribute to nitrogen input but that Ptilium crista-castrensis is the main contributor. Estimated nitrogen input by mosses (≪ 1 kg·ha−1·year−1) is in the low range of N inputs reported in the literature and is consistent with activities reported elsewhere for similar species, N deposition, and forest age. Results show that atmospheric deposition, while low, remains a more significant source of exogenous N to mature black spruce forests than bryophytes.