Bryophytes have an important biogeochemical role in many forest ecosystems, where they regulate soil temperature and moisture and influence carbon and nitrogen (N) cycling. Associations between bryophytes and N2-fixing cyanobacteria have been reported in northern latitude forests and are shown to provide a substantial N input to these ecosystems, but whether the association extends into temperate forests remains largely unknown. We investigated the extent of bryophyte-cyanobacteria associations in common understory bryophytes in a temperate forest in New York using δ15N analyses and ultraviolet fluorescence microscopy. Of the seven taxa examined, three (Fissidens taxifolius, Marchantia polymorpha, and Thuidium delicatulum) were associated with cyanobacteria, with colonization observed in 15–85% of the leaves examined. The taxa with cyanobacterial associations exhibited δ15N values that were 3.9‰ higher compared with taxa that did not, and the δ15N signatures were close to the atmospheric N2 signature of zero, suggesting these taxa acquired a measurable fraction of their N from associated cyanobacteria. Taxa that associated with cyanobacteria also had 55% higher tissue %N that did those not associated with cyanobacteria. This study revealed the utility of natural abundance stable N isotope analysis in detecting bryophyte-cyanobacteria symbioses, and also suggests that bryophyte-cyanobacteria associations may represent a significant yet previously unaccounted for N source to the temperate forest biome.
stable N isotope analysis