Original paper

Competition among freshwater phytoplankton species for ammonium in flow-through cultures

Shafik, Hesham M.; Herodek, Sándor; Présing, Mátyás; Vörös, Lajos


A competition experiment was performed in chemostat cultures with different nutrient treatments using phytoplankton from Lake Balaton, Hungary. The inflowing medium was natural lake water enriched with orthophosphate at a concentration of 100 μg l−1. In the continuous supply culture (CS) the ammonium concentration of the inflowing medium was 200 μg.l−1. Ammonium was injected once daily in the pulsed supply culture (PS). The third culture was run with no N supply (NNS). Large cell volume algae had been excluded from each culture for one to two weeks. Planktolyngbya subtilis was dominant in the CS. Its success may have depended more on the mode of nutrient supply, through a lower half saturation constant, than on nitrogen limitation. In the PS, Nitzschia spp. were the dominant algae along with some Chlorophyta, which may be the result of a high silicon concentration. The results of NNS show that algae could not grow in the culture without ammonium addition. Ammonium uptake in the CS and the PS was measured with 15N methodology at the end of the experiments. The KS and Vmax values were twice as high in the PS (18.7 μg.l−l and 85.1 μg.l−l.h−1) as in the CS (9.2 μg.l−l and 40.8 μg.l−l.h−1). But the ratios of kinetic parameters (α = Vmax/KS) were very similar in the CS and the PS.


phytoplanktoncompetitionnitrogen limitationammonium uptakeflow-through culturescontinuous culture