Summary:

The intrinsically linked global carbon and nitrogen cycles underpin the functioning of coastal wetlands. Nitrogen availability strongly influences the effect of elevated CO₂ on plant communities and their capacity to sequester carbon. However, the relative importance of different nitrogen forms to plant nutrition under future climate conditions in wetlands is unknown.  We investigated the capacity of two dominant wetland plant species, Spartina patens and Schoenoplectus americanus, to assimilate dissolved organic nitrogen under elevated CO₂ conditions. Our results show direct assimilation of dissolved organic nitrogen by these salt marsh species. Spartina patens uptake rates of glycine were twice that of Schoenoplectus americanus.  These results further our understanding of differences among species in nitrogen form acquisition, competitive dynamics between species, and habitat-level responses to global change.