Dinitrogen Fixation in Aphotic Oxygenated Marine Environments

Authors

Eyal Rahav
Edo Bar-Zeev
Sarah Ohayon
Hila Elifantz
Natalia Belkin
Barak Herut
Margaret R. Mulholland, Old Dominion UniversityFollow
IIana Berman-Frank

Document Type

Article

Publication Date

2013

DOI

10.3389/fmicb.2013.00227

Publication Title

Frontiers in Microbiology

Volume

4

Pages

1-11

Abstract

We measured N₂ fixation rates from oceanic zones that have traditionally been ignored as sources of biological N₂fixation; the aphotic, fully oxygenated, nitrate (NO¯₃)-rich, waters of the oligotrophic Levantine Basin (LB) and the Gulf of Aqaba (GA). N₂ fixation rates measured from pelagic aphotic waters to depths up to 720 m, during the mixed and stratified periods, ranged from 0.01 nmol N L^-1 d^-1 to 0.38 nmol N L^-1 d^-1. N₂ fixation rates correlated significantly with bacterial productivity and heterotrophic diazotrophs were identified from aphotic as well as photic depths. Dissolved free amino acid amendments to whole water from the GA enhanced bacterial productivity by 2-3.5 fold and N₂ fixation rates by similar to 2-fold in samples collected from aphotic depths while in amendments to water from photic depths bacterial productivity increased 2-6 fold while N₂ fixation rates increased by a factor of 2 to 4 illustrating that both BP and heterotrophic N₂ fixation were carbon limited. Experimental manipulations of aphotic waters from the LB demonstrated a significant positive correlation between transparent exopolymeric particle (TEP) concentrations and N₂ fixation rates. This suggests that sinking organic material and high carbon (C): nitrogen (N) micro-environments (such as TEP-based aggregates or marine snow) could support high heterotrophic N₂ fixation rates in oxygenated surface waters and in the aphotic zones. Indeed, our calculations show that aphotic N₂ fixation accounted for 37 to 75% of the total daily integrated N₂ fixation rates at both locations in the Mediterranean and Red Seas with rates equal or greater to those measured from the photo layers. Moreover, our results indicate that that while N₂ fixation may be limited in the surface waters, aphotic, pelagic N₂ fixation may contribute significantly to new N inputs in other oligotrophic basins, yet it is currently not included in regional or global N budgets.

Original Publication Citation

Rahav, E., Bar-Zeev, E., Ohayon, S., Elifantz, H., Belkin, N., Herut, B., . . . Berman-Frank, I. (2013). Dinitrogen fixation in aphotic oxygenated marine environments. Frontiers in Microbiology, 4, 1-11. doi: 10.3389/fmicb.2013.00227

Repository Citation

Rahav, Eyal; Bar-Zeev, Edo; Ohayon, Sarah; Elifantz, Hila; Belkin, Natalia; Herut, Barak; Mulholland, Margaret R.; and Berman-Frank, IIana, "Dinitrogen Fixation in Aphotic Oxygenated Marine Environments" (2013). OES Faculty Publications. 166.
https://digitalcommons.odu.edu/oeas_fac_pubs/166