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JOURNAL OF PLANKTON RESEARCH | VOLUME 19 | NUMBER 12 | PAGES 1899-1912 | 1997
© Oxford University Press
research-article |
Growth kinetic parameters of two planktonic desmid species under fluctuating phosphorus conditions in continuous-flow culture
Department of Aquatic Ecology, University of Amsterdam Kruislaan 320, NL-1098 SM Amsterdam, The Netherlands
Received on April 9, 1997; accepted on August 11, 1997 Two planktonic desmid taxa, Staurastrum chaetoceras and Cosmarium abbreviatum var. planctonicum, were examined under pulsed phosphorus (P)-limited conditions in continuous culture. Two pulse regimes were applied, i.e. 2.5 µM P twice a week and 10 µM P once every 2 weeks. Under both pulse regimes, S.chaetoceras showed a higher maximum P uptake rate (Vmax) and affinity for P uptake (Vmax/affinity constant Km) than C.abbreviatum. Affinity for P uptake in S.chaetoceras just before pulsing was higher than shortly after pulsing, whereas C.abbreviatum did not show any significant difference. Cell densities and cellular P quota in S.chaetoceras and C.abbreviatum fluctuated in a comparable way, but fluctuations in C.abbreviatum were less pronounced than in S.chaetoceras. The mean cell volume of both species was greater under the bimonthly than under the biweekly pulse regime, and the lowest under continuous P-limited conditions. Competition between S.chaetoceras and C.abbreviatum under the bimonthly pulse regime was won by S.chaetoceras, but displacement was less fast than under more frequent pulsing (equalling the same total P supply). The above-mentioned results are discussed in relation to possible ecological strategies.