Denitrification as the dominant nitrogen loss process in the Arabian Sea

Primary production in over half of the world’s oceans is limited by fixed nitrogen availability. The main loss term from the fixed nitrogen inventory is the production of dinitrogen gas (N2) by heterotrophic denitrification or the more recently discovered autotrophic process, anaerobic ammonia oxida...

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Bibliographic Details
Published in:	Nature (London) Vol. 461; no. 7260; pp. 78 - 81
Main Authors:	Chang, B. X, Pratihary, Anil, Rich, J. J, Devol, A. H, Jayakumar, A, Bulow, S. E, Ward, B. B, Naik, Hema
Format:	Journal Article
Language:	English
Published:	London Nature Publishing Group UK 03-09-2009 Nature Publishing Group
Subjects:	Anaerobiosis Animal and plant ecology Animal, plant and microbial ecology Arabia Bacteria Bacteria - genetics Bacteria - metabolism Biological and medical sciences Carbon - metabolism Carbon dioxide Denitrification Environmental aspects Fundamental and applied biological sciences. Psychology Gases - metabolism Humanities and Social Sciences letter Methods Microbiology multidisciplinary Nitrites - metabolism Nitrogen Nitrogen - metabolism Nitrogen cycle Nitrogen Fixation Oceans and Seas Oxidation-Reduction Oxygen - metabolism Pacific Ocean Quaternary Ammonium Compounds - metabolism RNA, Ribosomal, 16S - genetics Science Sea water ecosystems Seawater - chemistry Seawater - microbiology Synecology Indian Ocean Arabian Sea Arabia Pacific Ocean India Marine environment Denitrification Ammonia Oxidation Nitrogen Loss
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Summary:	Primary production in over half of the world’s oceans is limited by fixed nitrogen availability. The main loss term from the fixed nitrogen inventory is the production of dinitrogen gas (N2) by heterotrophic denitrification or the more recently discovered autotrophic process, anaerobic ammonia oxidation (anammox). Oceanic oxygen minimum zones (OMZ) are responsible for about 35% of oceanic N2 production and up to half of that occurs in the Arabian Sea. Although denitrification was long thought to be the only loss term, it has recently been argued that anammox alone is responsible for fixed nitrogen loss in the OMZs. Here we measure denitrification and anammox rates and quantify the abundance of denitrifying and anammox bacteria in the OMZ regions of the Eastern Tropical South Pacific and the Arabian Sea. We find that denitrification rather than anammox dominates the N2 loss term in the Arabian Sea, the largest and most intense OMZ in the world ocean. In seven of eight experiments in the Arabian Sea denitrification is responsible for 87–99% of the total N2 production. The dominance of denitrification is reproducible using two independent isotope incubation methods. In contrast, anammox is dominant in the Eastern Tropical South Pacific OMZ, as detected using one of the isotope incubation methods, as previously reported. The abundance of denitrifying bacteria always exceeded that of anammox bacteria by up to 7- and 19-fold in the Eastern Tropical South Pacific and Arabian Sea, respectively. Geographic and temporal variability in carbon supply may be responsible for the different contributions of denitrification and anammox in these two OMZs. The large contribution of denitrification to N2 loss in the Arabian Sea indicates the global significance of denitrification to the oceanic nitrogen budget.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0028-0836 1476-4687
DOI:	10.1038/nature08276