Synergistic effects of nitrate and ammonium ion on the growth and uptake kinetics of Monochrysis lutheri in continuous culture

Continuous-culture results for Monochrysis lutheri grown on 12 h light-12 h dark cycles with a spectrum of ratios of nitrate and ammonium serving as limiting nutrients are compared with continuous light, exclusively nitrate, and exclusively ammonium-limited data for this species. The diel effects of the light regime on the maximum specific uptake rate are examined for both nitrate and ammonium. Synergistic effects on uptake by various initial concentrations of these two nutrients are presented. Preconditioning with light-dark cycles did not affect maximum uptake rate, but preconditioning on a combination of nitrate and ammonium gave much lower uptake rates than those observed for populations preconditioned on either nutrient exclusively. The implications of high maximum specific-uptake rates compared to maximum specific-growth rates in terms of the range of nitrate and ammonium ion concentrations associated with nutrient limitation are reviewed.Hawaii Institute of Marine Biology Contribution No. 477.