The Nitrogen Uptake Kinetics of Spartina Alterniflora in Culture

Rates of nitrogen uptake were measured in cultures of Spartina alterniflora growing outdoors in continuously flowing nutrient solutions. A Michaelis—Menten model with V m a x expressed as an exponential function of temperature was an accurate predictor of uptake rates during the growing season. Half—saturation constants were estimated to be 0.057 @+ 0.016 mg N/L for NH 4 and 0.124 @+ 0.034 mg N/L for NO 3 . These half—saturation constants are too low in comparison to levels of inorganic NH 4 in marsh pore water to account for nitrogen—limited growth in the field. It was suggested that an edaphic factors(s), possibly an oxygen deficiency, or a metabolic poison such as H 2 S, or competition from other ions for carriers, might inhibit nitrogen uptake in the marsh in such a way as to increase the half—saturation constant for uptake. A gradient of such an environmental factor could account for gradients in morphology and productivity in communities of Spartina alterniflora.