Abstract: Bryophytes play key roles in ecosystems in terms of regulating soil microclimate and in carbon and nitrogen (N) cycles. Associations between bryophytes and N-fixing bacteria are a significant source of N in boreal forests and may also be important in temperate ecosystems. However, the extent to which these processes are applicable to the boreal-temperate ecotone, which includes a mosaic of deciduous, mixed, and coniferous forests, remains unknown. It is increasingly recognized that these associations are widespread across species and that the focus on a few very common species limits our understanding of this process at the community level. The objective of this project was to characterize the presence of cyanobacteria and the rate of nitrogen fixation on bryophyte species found in red spruce (Picea rubens)-dominated forests in Fundy National Park (FNP; New Brunswick). In 2021, we opportunistically harvested samples from two liverwort and eleven moss species from two sites (71 bryophyte samples) and measured environmental covariates (e.g., canopy composition, soil pH). Samples were brought back to the lab and used for measurements of nitrogen fixation, isotopic composition and cyanobacterial abundance. N-fixation was measured directly by incubating 10-20 stems from each sample for 24h in a growth chamber (20°C, 18h light-6hours dark) in syringes filled with 10 ml of air and 10 ml of 98% 15N2 gas. These incubated stems plus 10-20 stems used for estimates of the natural abundance of 15N were then dried (72h at 60°C), ground, and analyzed on an elemental analyzer coupled to a mass spectrometer to obtain isotopic ratios. Cyanobacteria abundance was measured by phycocyanin extraction and spectrofluorometry analysis on 10 stems from each sample. All bryophyte species investigated presented measurable N-fixation. This included feather mosses which are well-known to associated with N-fixing microbes, as well as less studied acrocarpous and pleurocarpous mosses and leafy liverworts. Our combined approach will allow for a first assessment of the role of the bryosphere in the Wabanaki-Acadian forest and will help to identify target species for subsequent studies.
