Upon the onset of anaerobic conditions in the rhizospheres of Spartina alterniflora Loisel. and S. patens (Aiton) Muhl., the root weight-specific uptake rates ( V max ) of NH + 4 decreased by 60% and 40%, respectively. This result can account for the nitrogen limitation of growth found in the short S. alterniflora plants in salt marshes. Increasing the salinity of aerobic nutrient solutions from 3%. to 32%. decreased V max by 30% in both species; while under anoxic conditions this same increase in salinity decreased V max in S. patens by 57% but had no effect on S. alterniflora. The uptake inhibition in S. patens at high salinity and anoxia may provide insight into the factors that control the distribution of this species within a marsh. Under most conditions tested, S. patens had equivalent or higher specific uptake rates than S. alterniflora; in outdoor cultures the specific uptake rates by S. patens were about five times greater. However, the accumulation of nitrogen per unit of growth, 11.0 and 20.9 mg N/g dry wt for S. alterniflora and S. patens respectively, were less different because S. patens maintained a lower ratio of root: total plant weight.