Nitrogen Nutrition and Salinity Tolerance of Distichlis Spicata and Spartina Alterniflora

In a greenhouse investigation Distichlis spicata (L.) and Spartina alterniflora (Loisel.) were grown from seed on freshwater, brackish, and marine sediments. These species were also concurrently grown in sand culture under conditions of nitrogen or phosphorus limitation in order to establish critical tissue concentrations of these elements. These experimentally determined values were used to assess the limiting nutrient status of the plants grown on the sediments. Growth of both species was nitrogen limited on most sediments, and phosphorus was consumed luxuriously on all sediments. Aboveground biomass was correlated with interstitial water nitrogen concentration of the sediments. Under low nutrient conditions relatively more biomass was allocated to belowground rather than aboveground portions of the plants. Although the availability of nitrogen ultimately determined biomass accrual, growth rate was affected by the sediment salinity. Analysis of plant tissues and the sediment interstitial water at the end of the investigation revealed selective uptake of potassium and exclusion of sodium. These processes increased the ratio of sodium to potassium in the interstitial waters and also resulted in increased sediment salinities. The effect of salinity stress on plant growth in Spartina marshes is discussed in relation to nitrogen limitation.