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Aquatic Microbial Ecology

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AME 77:111-123 (2016)  -  DOI:

Inorganic phosphorus enrichments in Baltic Sea water have large effects on growth, carbon fixation, and N2 fixation by Nodularia spumigena 

Malin Olofsson1,*, Jenny Egardt2, Arvind Singh3, Helle Ploug

1Department of Marine Sciences, University of Gothenburg, Box 460, 405 30 Göteborg, Sweden
2Department of Biological and Environmental Sciences, University of Gothenburg, Box 461, 405 30 Göteborg, Sweden
3Geosciences Division, Physical Research Laboratory, Navrangpura 380 009, Ahmedabad, India
*Corresponding author:

ABSTRACT: Two strains of the filamentous N2-fixing cyanobacterium Nodularia spumigena were inoculated separately in Baltic Sea water, and their growth, carbon (C)-fixation, and N2-fixation rates were monitored during a 21 d laboratory experiment. Low amounts of P (1 µM final concentration) were added to otherwise un-amended Baltic Sea water (<0.5 µM P). Exponential growth was stimulated under P-enriched conditions, indicating that the natural Baltic Sea water contained all residual nutrients essential for growth, and that N. spumigena was limited by P. The molar ratio of C to N2 fixation was >15 when ammonium was present at concentrations >5 µM on Day 0. This ratio was significantly different between the 2 strains, which indicated variable affinity for ammonium. It decreased in both strains as the ammonium concentration and C assimilation decreased and N2 fixation increased during the experiment. After 7 d, C- and N2-fixation rates co-varied with a relatively stable C:N fixation ratio close to or below the C:N ratio of cells (range: 4.7 to 8.6). The C:N cellular ratio and the specific N2 fixation varied significantly between strains, emphasizing the variability of eco-physiology between strains within the same species. The average growth rate during the experiment, the accumulated biomass, and the total N2-fixation rate were significantly higher under P-enriched compared to P-limited conditions in both strains. Hence, summers with high influx of P may stimulate growth, CO2 sequestration, and N2 fixation by N. spumigena in the Baltic Sea.

KEY WORDS: Heterocystous cyanobacteria · Baltic Sea · Nutrient limitation · Carbon sequestration · N2 fixation · Stable isotopes

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Cite this article as: Olofsson M, Egardt J, Singh A, Ploug H (2016) Inorganic phosphorus enrichments in Baltic Sea water have large effects on growth, carbon fixation, and N2 fixation by Nodularia spumigena . Aquat Microb Ecol 77:111-123.

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