First evidence of nitrogen fixation associated with bryophytes from coastal Wabanaki–Acadian forests

Abstract

Associations between bryophytes and dinitrogen (N2)-fixing bacteria are a significant source of exogenous N in unmanaged boreal and possibly temperate ecosystems. However, the extent to which biological N2-fixation (BNF) applies to the boreal–temperate ecotone remains elusive. The current focus on common species limits our understanding of BNF at the community level. Our objective was to characterize the presence of cyanobacteria and BNF activity associated with bryophytes in the coastal forests of Fundy National Park (New Brunswick, Canada). In 2021, we harvested three liverwort and 11 moss species from two sites (71 samples) and measured environmental covariates (e.g., canopy composition and soil pH). We used stable isotope incubations with 15N2 gas in growth chambers to quantify potential BNF activity and used phycocyanin extractions as a cyanobacteria abundance proxy. Many species presented detectable BNF rates, which were similar to or higher than those of well-studied feather mosses. These included species that have rarely been found to contribute to BNF. While cyanobacteria were present on most samples, we found no positive association between abundance and BNF. Our findings are among the first records for bryophyte-associated BNF in the boreal–temperate ecotone of eastern Canada and offer insights into the potential role of this process in N cycling in coastal conifer-dominated forests.