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Unicellular Cyanobacterial Distributions Broaden the Oceanic N2 Fixation Domain

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Science  25 Feb 2010:
1185468
DOI: 10.1126/science.1185468

Abstract

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 (1, 2). 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 significant contributor to open ocean N2 fixation. The distributions and activity of the two UCYN were separated as a function of depth, temperature, and water column density structure along a 8000 km transect in the South Pacific Ocean. UCYN-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 basin-scale oceanic N2 fixation rates.