Nitrogen-limited growth of marine phytoplankton—II. Uptake kinetics and their role in nutrient limited growth of phytoplankton

Abstract

The kinetics of nutrient uptake for nitrate ion are developed for four species of phytoplankton, and for ammonium ion for two species of phytoplankton. All cases are shown to be well described by the Michaelis-Menten hyperbolas. The two sets of half-saturation constants do not show significant interspecific variation, nor do they show intraspecific variation with different steady-state preconditioning growth rates. The maximum uptake rate parameter shows marked intraspecific variability that is positively correlated with the preconditioning growth rate of the population. This linear function, combined with the limiting nutrient uptake hyperbola and the relation between growth rate and the nutritional state of the population developed in Part I of this paper, provides a model that relates steady-state growth rate to environmental substrate concentration. The model is used to explain the failure to observe significant growth rate related variation in environmental limiting nutrient concentration at different steady-state growth rates in the chemostat. The evidence suggests that this model would be applicable to field situations for a mixed phytoplankton population in either a nitrate- or ammonium-limited environment, but the very low range of nutrient concentration involved would require more precision in nutrient analysis than is presently available.