COMPARISON OF HALF-SATURATION CONSTANTS FOR GROWTH AND NITRATE UPTAKE OF MARINE PHYTOPLANKTON

Growth rates and rates of nitrate uptake by N‐depleted cells were measured for an oceanic diatom, Chaetoceros gracilis, and a neritic diatom, Asterionella japonica, as functions of nitrate concentration of the medium. Both growth and N‐uptake rates appeared to be hyperbolic with nitrate concentration and could be fit to an equation of Michaelis‐Menten form: where v is rate, Vm. is the maximum rate, S is nitrate concentration, and Ksis the half‐saturation constant. Ksvalues for uptake and growth were similar if not identical for each species. Uptake experiments can provide a presumptive measure of Ksfor growth, thought to be an ecologically significant characteristic of a species. Copyright © 1969, Wiley Blackwell. All rights reserved