Effect of nitrogen forms on growth, cell composition and N₂ fixation of Cylindrospermopsis raciborskii in phosphorus-limited chemostat cultures

• Published in: Hydrobiologia 2009-05, Vol.623 (1), p.191-202
• Main Authors: Kenesi, Gyöngyi, Shafik, Hesham M, Kovács, Attila W, Herodek, Sándor, Présing, Mátyás
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Bacteria; Biological and medical sciences; Biomedical and Life Sciences; Carotenoids; Chlorophyll; Ecology; Freshwater & Marine Ecology; Fundamental and applied biological sciences. Psychology; General aspects; Life Sciences; Nitrogen; Nitrogen fixation; Nutrients; Phosphorus; Primary Research Paper; Studies; Synecology; Zoology
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1007/s10750-008-9657-9

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 (200 μg l⁻¹ PO₄-P) chemostat cultures of C. raciborskii using an inflowing medium containing either 4,000 μg l⁻¹ NH₄-N, 4,000 μg l⁻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.