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Nitrogen fixation by Trichodesmium and small diazotrophs in thesubtropical northeast Atlantic
Benavides, M.; Agawin, N.S.R.; Aristegui, J.; Ferriol, P.; Stal, L.J. (2011). Nitrogen fixation by Trichodesmium and small diazotrophs in thesubtropical northeast Atlantic. Aquat. Microb. Ecol. 65(1): 43-53. dx.doi.org/10.3354/ame01534
In: Aquatic Microbial Ecology. Inter-Research: Oldendorf/Luhe. ISSN 0948-3055, more
Peer reviewed article  

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Keyword
    Trichodesmium Ehrenberg ex Gomont, 1892 [WoRMS]
Author keywords
    Nitrogen fixation; Trichodesmium; Upwelling; Subtropical northeastAtlantic; Canary Current Large Marine Ecosystem

Authors  Top 
  • Benavides, M.
  • Agawin, N.S.R.
  • Aristegui, J.
  • Ferriol, P.
  • Stal, L.J.

Abstract
    We measured gross and net nitrogen fixation in fractionated samples (organisms > 10 mu m and < 10 mu m), 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 mu mol 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(-1)d(-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 mu m fraction contributed more to both gross and net nitrogen fixation than did the > 10 mu m fraction in most of the areas studied. The < 10 mu m 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.

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