Volume 20, Issue 12 p. 4281-4296
Research article

Widespread nitrogen fixation in sediments from diverse deep-sea sites of elevated carbon loading

Anne E. Dekas

Corresponding Author

Anne E. Dekas

Department of Earth System Science, Stanford University, Stanford, CA, 94305 USA

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125 USA

For correspondence. E-mail [email protected]; Tel. (+1) 650-736-1225. E-mail [email protected]; Tel. (+1) 626-395-1786Search for more papers by this author
David A. Fike

David A. Fike

Department of Earth & Planetary Sciences, Washington University in St. Louis, St. Louis, MO, 63130 USA

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Grayson L. Chadwick

Grayson L. Chadwick

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125 USA

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Abigail Green-Saxena

Abigail Green-Saxena

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125 USA

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Julian Fortney

Julian Fortney

Department of Earth System Science, Stanford University, Stanford, CA, 94305 USA

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Stephanie A. Connon

Stephanie A. Connon

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125 USA

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Katherine S. Dawson

Katherine S. Dawson

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125 USA

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Victoria J. Orphan

Corresponding Author

Victoria J. Orphan

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125 USA

For correspondence. E-mail [email protected]; Tel. (+1) 650-736-1225. E-mail [email protected]; Tel. (+1) 626-395-1786Search for more papers by this author
First published: 02 July 2018
Citations: 37

Summary

Nitrogen fixation, the biological conversion of N2 to NH3, is critical to alleviating nitrogen limitation in many marine ecosystems. To date, few measurements exist of N2 fixation in deep-sea sediments. Here, we conducted > 400 bottle incubations with sediments from methane seeps, whale falls and background sites off the western coast of the United States from 600 to 2893 m water depth to investigate the potential rates, spatial distribution and biological mediators of benthic N2 fixation. We found that N2 fixation was widespread, yet heterogeneously distributed with sediment depth at all sites. In some locations, rates exceeded previous measurements by > 10×, and provided up to 30% of the community anabolic growth requirement for nitrogen. Diazotrophic activity appeared to be inhibited by pore water ammonium: N2 fixation was only observed if incubation ammonium concentrations were ≤ 25 μM, and experimental additions of ammonium reduced diazotrophy. In seep sediments, N2 fixation was dependent on CH4 and coincident with sulphate reduction, consistent with previous work showing diazotrophy by microorganisms mediating sulphate-coupled methane oxidation. However, the pattern of diazotrophy was different in whale-fall and associated reference sediments, where it was largely unaffected by CH4, suggesting catabolically different diazotrophs at these sites.