Unicellular Cyanobacterial Distributions Broaden the Oceanic N2 Fixation Domain

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Science  19 Mar 2010:
Vol. 327, Issue 5972, pp. 1512-1514
DOI: 10.1126/science.1185468

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Nitrogen (N2)–fixing microorganisms (diazotrophs) are an important source of biologically available fixed N in terrestrial and aquatic ecosystems and control the productivity of oligotrophic ocean ecosystems. We found that two major groups of unicellular N2-fixing cyanobacteria (UCYN) have distinct spatial distributions that differ from those of Trichodesmium, the N2-fixing cyanobacterium previously considered to be the most important contributor to open-ocean N2 fixation. The distributions and activity of the two UCYN groups were separated as a function of depth, temperature, and water column density structure along an 8000-kilometer transect in the South Pacific Ocean. UCYN group A can be found at high abundances at substantially higher latitudes and deeper in subsurface ocean waters than Trichodesmium. These findings have implications for the geographic extent and magnitude of basin-scale oceanic N2 fixation rates.

  • Present address: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 01238, USA.

  • Present address: Department of Microbiology, 403 Wing Hall, Cornell University, Ithaca, NY 14853, USA.

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