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Niche construction by non‐diazotrophs for N 2 fixers in the eastern tropical North Atlantic Ocean
Author(s) -
Singh Arvind,
Bach Lennart T.,
Fischer Tim,
Hauss Helena,
Kiko Rainer,
Paul Allanah J.,
Stange Paul,
Vandromme Pieter,
Riebesell Ulf
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl074218
Subject(s) - diazotroph , prochlorococcus , cyanobacteria , nitrogen fixation , trichodesmium , biogeochemical cycle , redfield ratio , biogeochemistry , phosphate , synechococcus , oceanography , nitrate , biology , tropical atlantic , geomicrobiology , nitrogenase , ecology , nutrient , geology , phytoplankton , microorganism , paleontology , bacteria , sea surface temperature , biochemistry , environmental biotechnology
Diazotrophic dinitrogen (N 2 ) fixation contributes ~76% to “new” nitrogen inputs to the sunlit open ocean, but environmental factors determining N 2 fixation rates are not well constrained. Excess phosphate (phosphate–nitrate/16 > 0) and iron availability control N 2 fixation rates in the eastern tropical North Atlantic (ETNA), but it remains an open question how excess phosphate is generated within or supplied to the phosphate‐depleted sunlit layer. Our observations in the ETNA region (8°N–15°N, 19°W–23°W) suggest that Prochlorococcus and Synechococcus , the two ubiquitous non‐diazotrophic cyanobacteria with cellular N:P ratios higher than the Redfield ratio, create an environment of excess phosphate, which cannot be explained by diapycnal mixing, atmospheric, and riverine inputs. Thus, our results unveil a new biogeochemical niche construction mechanism by non‐diazotrophic cyanobacteria for their diazotrophic phylum group members (N 2 fixers). Our observations may help to understand the prevalence of diazotrophy in low‐phosphate, oligotrophic regions.