A linear model of external interactions during uptake of different forms of inorganic nitrogen by microalgae

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Abstract
A simple model is described to deal with external interactions during uptake of two inorganic nitrogen sources supplied simultaneously to microalgae. It is based on classical competitive enzyme inhibition kinetics and involves three variables: the external concentrations of the two nitrogen compounds and an index of algal biomass. The applicability of such a simple model to examples taken in the literature indicates that complex phenomena such as feedback inhibition may not always need to be taken into account and that uptake is sometimes regulated solely by the three above variables. The model can explain not only the apparent inhibition of nitrate uptake by ammonium in many cases, but also the ‘inhibition’ of ammonium uptake by nitrate, a phenomenon for which no physiological explanation has so far been offered.