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Growth kinetic parameters of two planktonic desmid species under fluctuating phosphorus conditions in continuous-flow culture
Authors:Spijkerman, Elly   Coesel, Peter F.M.
Affiliation:Department of Aquatic Ecology, University of Amsterdam Kruislaan 320, NL-1098 SM Amsterdam, The Netherlands
Abstract:Two planktonic desmid taxa, Staurastrum chaetoceras and Cosmariumabbreviatum var. planctonicum, were examined under pulsed phosphorus(P)-limited conditions in continuous culture. Two pulse regimeswere applied, i.e. 2.5 µM P twice a week and 10 µMP once every 2 weeks. Under both pulse regimes, S.chaetocerasshowed a higher maximum P uptake rate (Vmax) and affinity forP uptake (Vmax/affinity constant Km) than C.abbreviatum. Affinityfor P uptake in S.chaetoceras just before pulsing was higherthan shortly after pulsing, whereas C.abbreviatum did not showany significant difference. Cell densities and cellular P quotain S.chaetoceras and C.abbreviatum fluctuated in a comparableway, but fluctuations in C.abbreviatum were less pronouncedthan in S.chaetoceras. The mean cell volume of both specieswas greater under the bimonthly than under the biweekly pulseregime, and the lowest under continuous P-limited conditions.Competition between S.chaetoceras and C.abbreviatum under thebimonthly pulse regime was won by S.chaetoceras, but displacementwas less fast than under more frequent pulsing (equalling thesame total P supply). The above-mentioned results are discussedin relation to possible ecological strategies.
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