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Closed Access item Short-term temporal variability of ammonium and urea uptake by Alexandrium Catenella (Dinophyta) in cultures

Authors:Jauzein, Cécile
Collos, Yves
Garcés, Esther
Vila, Magda
Masó, Mercedes
Keywords:Alexandrium catenella, ammonium, ammonium release, uptake kinetics, urea, temporal availability
Issue Date:Oct-2008
Publisher:Phycological Society of America
Citation:Journal of Phycology 44(5): 1136-1145 (2008)
Abstract:In batch cultures of four Mediterranean strains (from France, Italy, and Spain) of Alexandrium catenella (Whedon et Kof.) Balech growing on a daily light cycle, ammonium and urea uptake were estimated by the 15N tracer technique. Ammonium uptake could be described by Michaelis-Menten kinetics along a substrate gradient of 0.1-10 μgat N · L−1 for the four strains, while two different patterns were observed for urea uptake with Michaelis-Menten kinetics for one strain and linear kinetics for the others. In all cases, an increase in uptake rates with time was noted over the daylight period. This trend led to a net increase in the maximum uptake rate (Vmax; for saturable kinetics) and in the initial slope α. For ammonium, Vmax increased by a factor of 2-10 depending on the strain, and, for urea, the maximal uptake rates measured increased by a factor of 2-18. Temporal variations of half-saturation constants (Ks) for both nutrients did not show a clear trend. Increases in Vmax and α showed an acclimation of the cells' uptake system over time to a N pulse, which may be explained by the light periodicity. For two strains, extensive ammonium release was observed during urea assimilation. This mechanism removes urea from the medium, so it is no longer available to other potential competitors, but supplies N back to the medium in the form of ammonium. From a methodological point of view, the phenomenon leads to considerable underestimates of the contribution of urea to phytoplankton growth.
Description:10 pages, 4 figures, 3 tables Full text version available open access at http://archimer.ifremer.fr/doc/2008/publication-6416.pdf
Publisher version (URL):http://doi.org/10.1111/j.1529-8817.2008.00570.x
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