Heterotrophic and autotrophic contribution to dinitrogen fixation in the Gulf of Aqaba

Eyal Rahav, Barak Herut, Margaret R. Mulholland, Natalia Belkin, Hila Elifantz, Ilana Berman-Frank

Research output: Contribution to journalArticlepeer-review


We evaluated the seasonal contribution of heterotrophic and autotrophic diazotrophy to the total dinitrogen (N2) fixation in the photic zone of a pelagic station in the northern Gulf of Aqaba, Red Sea. N2 fixation rates were highest during a Trichodesmium bloom in winter (0.7 nmol N l-1 d-1), decreased 7-fold 1 wk later throughout the upper 200 m (∼0.1 nmol N l-1 d-1), and were significantly coupled with both primary and bacterial productivity. N2 fixation rates were generally higher in the upper 200 m (∼0.4 nmol N l-1 d-1) during the thermally stratified summer and were correlated solely with bacterial productivity. Experimental enrichment of seawater by phosphorus (P) enhanced bacterial productivity and N2 fixation rates during both seasons by 3- to 5-fold. Moreover, during the stratified season, experimental amendments to seawater applying a combination of the photosynthetic inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea and a mixture of amino acids increased both bacterial productivity and N2 fixation rates. Our findings from the northern Gulf of Aqaba indicate that in the photic zone, a shift occurs in the diazotrophic community from phototrophic and heterotrophic populations in winter, including the cyano bacteria Trichodesmium, to predominantly heterotrophic diazotrophs in summer. These hetero trophic diazotrophs may be both carbon and P limited as illustrated by their response to additions of P and amino acids.

Original languageEnglish
Pages (from-to)67-77
Number of pages11
JournalMarine Ecology - Progress Series
StatePublished - 2 Mar 2015
Externally publishedYes

Bibliographical note

Publisher Copyright:
© Inter-Research 2015.


  • Autotrophic diazotrophs
  • Bacterial productivity
  • Gulf of Aqaba
  • Heterotrophic diazotrophs
  • N fixation
  • P limitation
  • Primary productivity

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science
  • Ecology


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