Kinetics of nitrate and ammonium uptake by the tropical freshwater macrophyte Pistia stratiotes L.

Abstract

The kinetics of nitrogen uptake were examined for a common freshwater macrophyte Pistia stratiotes. Nitrate-nitrogen and ammonium-nitrogen uptake were monitored in response to a wide range of substrate concentrations. Nitrate uptake rates were higher after 24 h of exposure to the nitrate source than immediately after exposure. The rate of uptake of nitrate-nitrogen was greater in the light than in the dark. Nitrate uptake followed a pattern which could be adequately described by the Michaelis—Menten expression. Ammonium-nitrogen uptake response to substrate concentration appeared to be linear. Rates of ammonium-nitrogen uptake were similar in the dark and in the light. For any given dissolved nitrogen concentration, the rate of ammonium-nitrogen uptake was greater than the rate of nitrate-nitrogen uptake.