Chemiluminescent measurements of nitrate kinetics: I. Thalassiosira pseudonana (clone 3H) and neritic assemblages<xref ref-type="fn" rid="fn1"><sup>*</sup></xref>

Abstract

We report the use of a chemiluminescent nitrate method to measure the substrate concentration in chemostat cultures of the diatom Thalassiosira pseudonana (clone 3H) at a range of steady-state growth rates, and after making nanomolar nitrate perturbations to 3H cultures and neritic phytoplankton assemblages. The chemostat steady-state data were combined with data from an exponentially growing batch culture to calculate Michaehs-Menten coefficients, Kx and Vmax. The results can be summarized as follows: (1) Michaehs-Menten kinetics appear to be an appropriate description of the steady-state uptake of nitrate in 3H; (ii) small perturbations of the steady-state nitrate concentration resulted in kinetics that are not described by the standard Michaehs-Menten expression; (iii) perturbed uptake rates were initially higher than the steady-state rate, but declined to 0 before nitrate was exhausted, (iv) the ecological competition for nitrate can only be partly described by Michaehs-Menten coefficients, and the response to perturbations in nitrate concentrations is likely to be a competitive factor in species success.