The contamination of commercial 15N2 gas stocks with 15N-labeled nitrate and ammonium and consequences for 
nitrogen fixation measurements

Dabundo, R. and Lehmann, Moritz F. and Treibergs, L. and Tobias, C. L. and Altabet, M. A. and Moisander, P. H. and Granger, J.. (2014) The contamination of commercial 15N2 gas stocks with 15N-labeled nitrate and ammonium and consequences for 
nitrogen fixation measurements. PLoS ONE, Vol. 9, H. 10 , e110335. pp. 1691-1705.

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Official URL: http://edoc.unibas.ch/dok/A6337652

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We report on the contamination of commercial 15-nitrogen (N-15) N-2 gas stocks with N-15-enriched ammonium, nitrate and/or nitrite, and nitrous oxide. N-15(2) gas is used to estimate N-2 fixation rates from incubations of environmental samples by monitoring the incorporation of isotopically labeled N-15(2) into organic matter. However, the microbial assimilation of bioavailable N-15-labeled N-2 gas contaminants, nitrate, nitrite, and ammonium, is liable to lead to the inflation or false detection of N-2 fixation rates. N-15(2) gas procured from three major suppliers was analyzed for the presence of these N-15-contaminants. Substantial concentrations of N-15-contaminants were detected in four Sigma-Aldrich N-15(2) lecture bottles from two discrete batch syntheses. Per mole of N-15(2) gas, 34 to 1900 mmoles of N-15-ammonium, 1.8 to 420 mmoles of (15)Nnitrate/nitrite, and <= 21 mmoles of N-15-nitrous oxide were detected. One N-15(2) lecture bottle from Campro Scientific contained <= 11 mmoles of N-15-nitrous oxide per mole of N-15(2) gas, and no detected N-15-nitrate/nitrite at the given experimental N-15(2) tracer dilutions. Two Cambridge Isotopes lecture bottles from discrete batch syntheses contained <= 0.81 mu moles N-15-nitrous oxide per mole (15)N2, and trace concentrations of N-15-ammonium and N-15-nitrate/nitrite. N-15(2) gas equilibrated cultures of the green algae Dunaliella tertiolecta confirmed that the N-15-contaminants are assimilable. A finite-differencing model parameterized using oceanic field conditions typical of N-2 fixation assays suggests that the degree of detected N-15-ammonium contamination could yield inferred N-2 fixation rates ranging from undetectable, >0.01 nmoles N L-1 d(-1), to 530 nmoles N L-1 d(-1), contingent on experimental conditions. These rates are comparable to, or greater than, N-2 fixation rates commonly detected in field assays. These results indicate that past reports of N-2 fixation should be interpreted with caution, and demonstrate that the purity of commercial N-15(2) gas must be ensured prior to use in future N-2 fixation rate determinations.
Faculties and Departments:05 Faculty of Science > Departement Umweltwissenschaften > Geowissenschaften > Aquatic and Isotope Biogeochemistry (Lehmann)
UniBasel Contributors:Lehmann, Moritz F
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:Public Library of Science
Note:Publication type according to Uni Basel Research Database: Journal article
Identification Number:
Last Modified:31 Aug 2018 06:39
Deposited On:06 Feb 2015 09:59

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