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ABSTRACT: The aim of this research was to test whether NH4
+ and NO3
− affect the growth, P demand, cell composition and N2 fixation of Cylindrospermopsis raciborskii under P limitation. Experiments were carried out in P-limited (200μgl−1 PO4-P) chemostat cultures of C. raciborskii using an inflowing medium containing either 4,000μgl−1 NH4-N, 4,000μgl−1 NO3-N or no combined N. The results showed the cellular N:P and C:P ratios of C. raciborskii decreased towards the Redfield ratio with increasing dilution rate (D) due to the alleviation of P limitation. The cellular C:N and carotenoids:chlorophyll-a ratios also decreased with D, predominantly as a result of an increase in the chlorophyll-a and N content. The NH4
+ and NO3
− supply reduced the P maintenance cell quota of C. raciborskii. Consequently, the biomass yield of the N2-grown culture was significantly lower. The maximum specific growth rate of N2-grown culture was also the lowest observed. It is suggested that these differences in growth parameters were caused by the
P and energy requirement for heterocyte formation, nitrogenase synthesis and N2 fixation. N2 fixation was partially inhibited by NO3
− and completely inhibited by NH4
+. It was probably repressed through the high N content of cells at high dissolved N concentrations. These results indicate
that C. raciborskii is able to grow faster and maintain a higher biomass under P limitation where a sufficient supply of NH4
+ or NO3
− is maintained. Information gained about the species-specific nutrient and pigment stoichiometry of C. raciborskii could help to access the degree of nutrient limitation in water bodies.
Hydrobiologia 04/2012; 623(1):191-202. · 1.78 Impact Factor
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ABSTRACT: A pico sized Synechococcus species isolated from Lake Balaton was studied in batch and continuous cultures. This picocyanobacterium had a pH optimum at 8.5 and a temperature optimum at 28-30°C. The Ik value for growth was 52 μEinstein m−2 S−1, the maximum growth rate 2.27 d−1, the half saturation Constant of growth 1.2 μg PO4-P I−1 and the minimal cell quota 1.74 nig P g dry weight−1. The dry weight of cells showed a minimum, the chlorophyll-a/biomass ratio a maximum as a function of growth rate. Above the quota of 3.4 fg P Cell−1 significant amounts of non-reactive dissolved Phosphorous were released.
Internationale Revue der gesamten Hydrobiologie und Hydrographie 11/2010; 81(4):503 - 512.
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ABSTRACT: 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.
Algological Studies 04/2004; 112(1):157-176.
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ABSTRACT: Ammonium and nitrate uptake and N2-fixation of the heterocystous cyanoprokaryote Cylindrospermopsis raciborskii was examined in continuous cultures under different nitrogen concentrations and dilution rates using the 15N technique. It was found that at luxury phosphorus supply (5 mg PO4-P l–1) the biomass was similar in all cultures irrespective of the amount and portioning (continuous or pulsed) of available nitrogen forms. The added ammonium and nitrate was fully taken up by C. raciborskii and the remaining nitrogen demand was met by N2-fixation. Different ammonium concentrations (300, 750, 1500 and 3000 g 15N l–1) added at the same dilution rate did not affect the growth of C. raciborskii. In the culture supplied with pulsed ammonium, N2-fixation was detected prior to ammonium addition only. After the ammonium pulse, the N2-fixation continued for a while then decreased and stopped. In addition, the inflowing ammonium was fully taken up by the organism. The rate of nitrogen fixation reached its original level after 8–24 hours, depending on the dilution rate. It can be suggested that the nitrogen fixation system stopped and was then activated again depending on the nitrogen content of the cells.
Hydrobiologia 10/2003; 506-509(1):169-174. · 1.78 Impact Factor
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ABSTRACT: 1. The importance of various forms of nitrogen to the nitrogen supply of phytoplankton has been investigated in the mesotrophic eastern and eutrophic western basin of Lake Balaton. 2. Uptake rates of ammonium, urea, nitrate and carbon were measured simultaneously. The uptake rates were determined using N and C methodologies, and N2-fixation was measured using the acetylene-reduction method. The light dependence of uptake was described with an exponential saturation equation and used to calculate surface-related (areal) daily uptake. 3. The contribution of ammonium, urea and nitrate to the daily nitrogen supply of phytoplankton varied between 11 and 80%, 17 and 73% and 1 and 15%, respectively. N2-fixation was negligible in the eastern basin and varied between 5 and 30% in the western region of the lake. The annual external nitrogen load was only 10% of that utilized by algae. 4. The predominant process supplying nitrogen to the phytoplankton in the lake is the rapid recycling of ammonium and urea in the water column. The importance of the internal nutrient loading is emphasized.
Freshwater Biology 12/2000; 46(1):125 - 139. · 3.29 Impact Factor
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ABSTRACT: Seasonal variations of phyto-, bacterio- and colourless flagellate plankton were followed across a year in the large shallow Lake Balaton (Hungary). Yearly average chlorophyll-a concentration was 11 g 1–1, while the corresponding values of bacterioplankton and heterotrophic nanoflagellate (HNF) plankton biomass (fresh weight) were 0.24 mg 1–1 and 0.35 mg 1–1, respectively. About half of planktonic primary production was channelled through bacterioplankton on the yearly basis. However, there was no significant correlation between phytoplankton biomass and bacterial abundance. Bacterial specific growth rates were in the range of 0.009 and 0.09 h–1, and ended to follow the seasonal changes in water temperature. In some periods of the year, predator-prey relationships between the HNF and bacterial abundance were obvious. The estimated HNF grazing on bacteria varied between 3% and 227% of the daily bacterial production. On an annual basis, 87% of bacterial cell production was grazed by HNF plankton.
Hydrobiologia 10/1996; 339(1):57-65. · 1.78 Impact Factor
