Report Number: 10
Year: 1980

Nitrogen Uptake by Tropical Freshwater Macrophytes

The kinetics of nitrogen uptake were examined for three specimens of aquatic macrophytes which are common Guam. Nitrate-nitrogen and ammonium-nitrogen uptake by Pistia stratiotes were monitored in response to a wide range of substrate concentrations. First-order kinetics of nitrate-nitrogen uptake were examined for P. stratiotes, Hydrilla verticillata and Microspora sp. Uptake rates were higher after 24 hrs of exposure to the nitrate source than immediately after exposure. The rate of uptake of nitrate-nitrogen by P. stratiotes was greater in the light than in the dark. Nitrate uptake followed a pattern which could be described by the Michaelis-Menton expression. Rates of ammonium-nitrogen uptake were similar in the dark and in the light. Ammonium-nitrogen uptake response to substrate concentration appeared to be linear. For any given dissolved nitrogen concentration, the rate of ammonium-nitrogen uptake was greater than the rate of nitrate-nitrogen uptake.

Stephen G. Nelson
Barry D. Smith
Bruce R. Best