Nitrogen isotope fractionation by alternative nitrogenases and past ocean anoxia

Xinning Zhang, Daniel Mikhail Sigman, Francois M. M. Morel, Anne M.L. Kraepiel

Research output: Contribution to journalArticlepeer-review

149 Scopus citations


Biological nitrogen fixation constitutes the main input of fixed nitrogen to Earth's ecosystems, and its isotope effect is a key parameter in isotope-based interpretations of the N cycle. The nitrogen isotopic composition (δ15N) of newly fixed N is currently believed to be∼-10/00, based on measurements of organic matter from diazotrophs using molybdenum (Mo)-nitrogenases. We show that the vanadium (V)- and iron (Fe)-only "alternative" nitrogenases produce fixed N with significantly lower δ15N (-6 to -70/00). An important contribution of alternative nitrogenases to N2 fixation provides a simple explanation for the anomalously low δ15N (<-20/00) in sediments from the Cretaceous Oceanic Anoxic Events and the Archean Eon. A significant role for the alternative nitrogenases over Mo-nitrogenase is also consistent with evidence of Mo scarcity during these geologic periods, suggesting an additional dimension to the coupling between the global cycles of trace elements and nitrogen.

Original languageEnglish (US)
Pages (from-to)4782-4787
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number13
StatePublished - Apr 1 2014

All Science Journal Classification (ASJC) codes

  • General


  • Biogeochemistry
  • Paleooceanography
  • Stable isotopes
  • Trace metals


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