Hydrobiologia

, Volume 623, Issue 1, pp 191–202

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

Primary research paper

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 (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.

Keywords

Cylindrospermopsis raciborskii Heterocytic cyanobacteria Phosphorus limitation N2 fixation Chemostat 

Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  1. 1.Balaton Limnological Research Institute of the Hungarian Academy of SciencesTihanyHungary
  2. 2.Botany Department, Faculty of ScienceSuez Canal UniversityPort SaidEgypt

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