Nitrogen uptake kinetics of freshly isolated zooxanthellae

Abstract

Zooxanthellae freshly isolated from the coral host Pocillopora damicornis exhibited substrate-saturable uptake kinetics for ammonium, nitrate and urea. Maximum uptake velocity for ammonium [10.1 nmol. ( mu chl-a)./1h/1] was greater than that for nitrate [2.8 nmol. ( mu chl-a)./1h/1] and urea [0.37 nmol. ( mu chl-a)./1h/1]. Half-saturation constants for uptake of the three nitrogen compounds were in the range of 10-15 mu mol.l/1. Generally, uptake of any one nitrogen substrate appears to be inhibitEd. by the other 2 substrates when the latter are present in higher concentrations. The observed interactions can be explainEd. by the uncompetitive model. These results are interpreted as indicative of a simultaneous uptake of all 3 nitrogen compounds by the zooxanthellae