Influence of Oxygen and Sulfide Concentration on Nitrogen Uptake Kinetics in Spartina Alterniflora

The effects of sulfide concentration and hypoxia on NH 4 @ ?—uptake kinetics in Spartina alterniflora were examined in a laboratory culture experiment. Both factors significantly influenced the Michaelis—Menten parameters, V m a x and K m , which characterize the nitrogen uptake rate as a function of nitrogen concentration. Under oxygen—saturated conditions, the mean NH 4 @ ? V m a x per unit root dry mass (DM) was 12.91 @mmol°g — 1 °h — 1 and the K m was 1.05 @mmol/L NH 4 @ ?+. Under hypoxia, V m a x decreased to 8.14 @mmol°g — 1 °h — 1 , while K m increased to 2.54 @mmol/L NH 4 @ ?+. Dissolved sulfide concentrations as low as 0.25 mmol/L inhibited the NH 4 @ ?+—uptake kinetics of S. alterniflora significantly, and to a greater extent than hypoxia alone. Exposure to 1.0 mmol/L sulfide resulted in a V m a x per unit root DM of 2.28 @mmol°g — 1 °h — 1 and a K m of 8.79 mmol/L NH 4 @ ?+. No significant NH 4 @ ?+ uptake was found with exposure to 2.0 mmol/L sulfide. The results are consistent with a conceptual model of changes in productivity of S. alterniflora in the salt marsh as a function of environmental modification of NH 4 @ ?+—uptake kinetics.