Interactions of ammonium, nitrate, and D- and Lamino acids in the nitrogen assimilation of two species of estuarine benthic diatoms

Assimilation of D- and L-amino acids by axenic cultures of Navlcula salinarum and Amphiprora cf. paludosa was measured by High Performance Liquid Chromatography (HPLC) Ammonlum ions at concentrations of 5 to 100 pm01 l-' effectively suppressed the utilization of concentrations of 100 km01 l-' of nitrate, but d~d not eliminate the uptake of amino acids in concentrations
of 0.05 to 0.8 pm01 I-'. N. salinarum assimilated low concentrations of several amino acids parallel with high concentrations of ammonium, whereas A. cf. paludosa depleted the concentration of aspartic and glutamic acid more rapidly than that of ammonium. Nitrogen-depnved cultures of both species assimilated spikes of amino acids very rapidly: half of the concentration added was assimilated in 0.5 h. The assimilation of 6 D-amino acids was compared with that of the corresponding Lforms; the effect of the isomeric form on the uptake rate differed widely among the amino acids. The possible application of these uptake experiments to interstitial water is discussed.