M. Kirwan K. J. McGlathery J. C. Zieman T. J. Mozdzer 2011 The smooth cordgrass <i>Spartina alterniflora</i> is the foundation species in intertidal salt marshes of the North American Atlantic coast. Depending on its elevation within the marsh, <i>S. alterniflora</i> may be submerged for several hours per day. Previous ecosystem-level studies have demonstrated that <i>S. alterniflora</i> marshes are a net sink for nitrogen (N), and that removal of N from flooding tidal water can provide enough N to support the aboveground biomass. However, studies have not specifically investigated whether <i>S. alterniflora</i> plants assimilate nutrients through their aboveground tissue. We determined <i>in situ</i> foliar and stem N uptake kinetics for ¹⁵NH₄, ¹⁵NO₃, and ¹⁵N-glycine by artificially flooding plants in a mid-Atlantic salt marsh. To determine the ecological importance of shoot uptake, a model was created to estimate the time of inundation of <i>S. alterniflora</i> in 20 cm height intervals during the growing season. Estimates of inundation time, shoot mass, N uptake rates, and N availability from long-term data sets were used to model seasonal shoot N uptake. Rates of aboveground N uptake rates (leaves + stems) were ranked as follows: NH₄⁺ > glycine > NO₃^&ndash;. Our model suggests that shoot N uptake may satisfy up to 15% of the growing season N demand in mid-Atlantic salt marshes, with variation depending on plant elevation and water column N availability. However, in eutrophic estuaries, our model indicates the potential of the plant canopy as a nutrient filter, with shoot uptake contributing 66 to 100% of plant N demand. application/pdf 10.3354/meps09117 en Inter-Research Science Center Nitrogen uptake by the shoots of smooth cordgrass Spartina alterniflora article