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Aquatic Microbial Ecology

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AME 65:43-53 (2011)  -  DOI:

Nitrogen fixation by Trichodesmium and small ­diazotrophs in the subtropical northeast Atlantic

Mar Benavides1,*, Nona S. R. Agawin2, Javier Arístegui1, Pere Ferriol2, Lucas J. Stal3,4

1Instituto de Oceanografía y Cambio Global, Universidad de Las Palmas de Gran Canaria, 35017 Las Palmas de Gran Canaria, Spain
2Interdisciplinary Ecology Group, Biology Department, University of the Balearic Islands, 07122 Palma de Mallorca, Spain
3Netherlands Institute for Ecology, NIOO-KNAW, Department of Marine Microbiology, 4400 AC Yerseke, The Netherlands
4Department of Aquatic Microbiology, IBED, University of Amsterdam, 1090 GE Amsterdam, The Netherlands

ABSTRACT: We measured gross and net nitrogen fixation in fractionated samples (organisms >10 µm and <10 µm), and the density of Trichodesmium, during a cruise along the northeast Atlantic boundary current system and during 2 mesoscale experiments in the upwelling systems of Cape Silleiro (northwest Iberia) and Cape Ghir (northwest Africa). The density of Tricho­desmium (<0.5 trichomes l−1) and its associated rates of nitrogen fixation (<0.1 μmol N m−2 d−1) were low. Trichomes appeared to accumulate at frontal sites—such as upwelling filaments and the Azores Front. Gross and net rates of nitrogen fixation were always <0.4 nmol N l−1d−1 except off the northwest African coast where a gross nitrogen fixation peak of 0.98 nmol N l−1 d−1 was measured. The <10 µm fraction contributed more to both gross and net nitrogen fixation than did the >10 µm fraction in most of the areas studied. The <10 µm fraction was responsible for 70 to 92% of the total nitrogen fixation in cold nutrient-rich areas. The contribution of small diazotrophs to nitrogen fixation in the upwelling sites suggests that the distribution and activity of these organisms are more widespread than previously thought.

KEY WORDS: Nitrogen fixation · Trichodesmium · Upwelling · Subtropical northeast Atlantic · Canary Current Large Marine Ecosystem

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Cite this article as: Benavides M, Agawin NSR, Arístegui J, Ferriol P, Stal LJ (2011) Nitrogen fixation by Trichodesmium and small ­diazotrophs in the subtropical northeast Atlantic. Aquat Microb Ecol 65:43-53.

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