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
ABSTRACT: Since the middle of 1990s the trend of Lake Balaton towards an increasingly trophic status has been reversed, but N2-fixing cyanobacteria are occasionally dominant, endangering water quality in summer. The sources of nitrogen and its uptake
by growing phytoplankton were therefore studied. Experiments were carried out on samples collected from the middle of the
Eastern (Siófok) and Western (Keszthely) basins between February and October 2001. Ammonium, urea and nitrate uptake and ammonium
regeneration were measured in the upper 5-cm layer of sediment using the 15N-technique. Ammonium was determined by an improved microdiffusion assay. N2 fixation rates were measured by the acetylene-reduction method. Ammonium regeneration rates in the sediment were similar
in the two basins. They were relatively low in winter (0.13 and 0.16 µg N cm−3 day−1 in the Eastern and Western basin, respectively), increased slowly in the spring (0.38 and 0.45 µg N cm−3 day−1) and peaked in late summer (0.82 and 1.29 µg N cm−3 day−1, respectively). Ammonium uptake was predominant in spring in the Eastern basin and in summer in the Western basin, coincident
with the cyanobacterial bloom. The amount of N2 fixed was less than one third of the internal load during summer when external N loading was insignificant. Potentially,
the phytoplankton N demand could be supported entirely by the internal N load via ammonium regeneration in the water column
and sediment. However, the quantity of N from ammonium regeneration in the upper layer of sediment combined with that from
the water column would limit the standing phytoplankton crop in spring in both basins and in late summer in the Western basin,
especially when the algal biomass increases suddenly.
12/2007: pages 87-95;
ABSTRACT: Morphological characteristics of Cylindrospermopsis raciborskii were investigated in batch culture under P-starvation and in continuous cultures at two growth rates with different N forms. The species displayed an enormous morphological variability under controlled condition. In the P-starved batch culture very short and extreme morphology trichomes with conical or drop-shape heterocytes were formed. In continuous culture extremely long, twisted filaments were found near the maximum growth rate. Rarely, C. raciborskii formed intercalary heterocytes.
Hydrobiologia 10/2003; 506-509(1):163-167. · 1.78 Impact Factor
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
ABSTRACT: Remote sensing has been used extensively to provide quantitative information on the distribution of phytoplankton in inland waters through the surrogate mapping of chlorophyll a, but as chlorophyll a is common to almost all species of phytoplankton it cannot provide any information on the taxonomic composition of phytoplankton communities. However, the varied optical properties of phytoplankton taxa may present a means to their discrimination via remote sensing data. This paper presents the results of an experimental study in which the spectral dissimilarities of brown, green, blue-green and red algae were examined with a view to establishing a basis upon which broad changes in phytoplankton communities might be monitored through remote sensing. Pseudo phytoplankton communities were simulated in a series of mesocosm experiments from which spectral reflectance measurements were acquired. The results demonstrated that the phytoplankton colour groups examined were indeed spectrally dissimilar. The spectral distinction between colour groups was noted to be greatest at high concentrations of chlorophyll a and between pseudo-communities dominated by a single species; spectral differences were lower in mixed pseudo-communities with co-dominant species. Moreover, it proved possible to quantify the concentration of two potential biomarker pigments, fucoxanthin and C-phycocyanin, through the derivation of simple spectral indices. The coincidental presence of varying concentrations of SPM (SPIM and SPOM) caused significant attenuation of the spectral response of the pseudo-communities and affected the accuracy of biomarker pigment estimation. It is considered that the realisation of a remote sensing technique for the discrimination of phytoplankton taxa in inland waters would be an extremely useful tool for limnological research and water resource management and thus the future application of this research to inland waters is also discussed.
Remote Sensing of Environment.