@article{196,
  author = {R. *Darnajoux and L. *Reji and X.R. *Zhang and K.E. *Luxem and X. Zhang},
  title = {Ammonium Sensitivity of Biological Nitrogen Fixation by Anaerobic Diazotrophsin Cultures and Benthic Marine Sediments},
  abstract = {<p>New bioavailable nitrogen (N) from biological nitrogen fixation (BNF) is critical for the N\&nbsp;budget and productivity of marine ecosystems. Nitrogen-fixing organisms typically inactivate BNF when\&nbsp;less metabolically costly N sources, like ammonium (NH\&nbsp;4\&nbsp;+), are available. Yet, several studies have observed\&nbsp;BNF in benthic marine sediments linked to anaerobic sulfate-reducing bacteria and fermenting firmicutes\&nbsp;despite high porewater NH\&nbsp;4\&nbsp;+\&nbsp;concentrations (10{\textendash}1,500 μM). To better understand the regulating controls\&nbsp;and importance of benthic marine BNF, we evaluate BNF sensitivity to NH\&nbsp;4\&nbsp;+\&nbsp;in benthic diazotrophs using\&nbsp;incubations of increasing biogeochemical complexity. BNF by cultures of model anaerobic diazotrophs\&nbsp;(sulfate-reducer\&nbsp;Desulfovibrio vulgaris\&nbsp;var. Hildenborough, fermenter\&nbsp;Clostridium pasteurianum\&nbsp;strain W5),\&nbsp;sulfate-reducing sediment enrichment cultures, and sediments from three Northeastern salt marshes (USA) is\&nbsp;highly sensitive to external NH\&nbsp;4\&nbsp;+\&nbsp;. BNF is inhibited by NH4\&nbsp;+\&nbsp;beyond an apparent threshold [NH4\&nbsp;+\&nbsp;] of 2 μM in\&nbsp;liquid cultures, most closely reflecting the true cellular sensitivity of BNF to NH4\&nbsp;+. Sediment slurries exhibited\&nbsp;an apparent threshold [NH\&nbsp;4\&nbsp;+\&nbsp;] of 9 μM. Consistent with other studies, we find SRB-like nitrogenase (nifH) gene\&nbsp;and transcripts are prevalent in sediments. Our survey of porewater NH\&nbsp;4\&nbsp;+\&nbsp;data from diverse sediments suggests\&nbsp;the broad applicability of inhibition thresholds measured here and confinement of benthic BNF to surficial\&nbsp;sediments. Variations in BNF inhibition timing, NH\&nbsp;4\&nbsp;+\&nbsp;uptake rate, sediment composition, and biophysics could\&nbsp;affect measurements of the apparent sensitivity of benthic BNF to NH\&nbsp;4\&nbsp;+\&nbsp;. We propose NH4\&nbsp;+\&nbsp;transporter affinity\&nbsp;as a fundamental mechanistic constraint on NH4\&nbsp;+\&nbsp;control of cellular BNF to improve biogeochemical models of\&nbsp;N cycling.</p>
},
  year = {2022},
  journal = {Journal of Geophysical Research: Biogeosciences},
  volume = {127},
  month = {07/2022},
  url = {https://doi.org/10.1029/2021JG006596},
  doi = {10.1029/2021JG006596},
}