FACTORS CONTROLLING ABOVEGROUND SPARTINA-ALTERNIFLORA (SMOOTH CORDGRASS) TISSUE ELEMENT COMPOSITION AND PRODUCTION IN DIFFERENT-AGE BARRIER-ISLAND MARSHES

Aboveground production and tissue element composition of Spartina alte rniflora were compared in barrier island marshes of different age off the Eastern Shore of Virginia. The marshes were also characterized by physical and chemical parameters of the substrate. The results suggest that sediment nutrient stocks do not directly control the spatial pat tern of element content or production of S. alterniflora between these marshes. Elevated salinity likely limits the nitrogen uptake capabili ty of S. alterniflora in the high marsh, which, in turn, controls leaf tissue nitrogen content of plants within individual sites. Low substr ate redox potential may control the spatial pattern of nitrogen uptake between the different-age marsh sites, leading to more favorable grow ing conditions at the low stations of the young marsh sites where valu es of tissue nitrogen and production are highest. Tissue phosphorus di d not differ between or within the marsh sites. The results of a ferti lization experiment suggest that nitrogen, and not phosphorus, is the primary limiting nutrient in this system. This indicates that nutrient limitation and other stresses work in conjunction to control tissue e lement content and macrophyte production at these marsh sites. Spatial variability of factors that control leaf tissue nitrogen and producti on is likely related to topography and grain size of an individual mar sh, which is a function of marsh age. Most studies in different-age ma rshes have compared transplanted marshes to older, natural marshes. Th is work is one of few studies comparing developing and mature natural marshes on barrier islands.