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Nitrogen isotope fractionation by alternative nitrogenases and past ocean anoxia.


ABSTRACT: 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 (?(15)N) of newly fixed N is currently believed to be ?-1‰, 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 ?(15)N (-6 to -7‰). An important contribution of alternative nitrogenases to N2 fixation provides a simple explanation for the anomalously low ?(15)N (<-2‰) 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.

SUBMITTER: Zhang X 

PROVIDER: S-EPMC3977277 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature

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Nitrogen isotope fractionation by alternative nitrogenases and past ocean anoxia.

Zhang Xinning X   Sigman Daniel M DM   Morel François M M FM   Kraepiel Anne M L AM  

Proceedings of the National Academy of Sciences of the United States of America 20140317 13


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 (δ(15)N) of newly fixed N is currently believed to be ∼-1‰, 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 δ(15)N  ...[more]

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