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Correcting for background nitrate contamination in KCl-extracted samples during isotopic analysis of oxygen and nitrogen by the denitrifier method

2014; Wiley; Volume: 28; Issue: 5 Linguagem: Inglês

10.1002/rcm.6824

1097-0231

Michael D. Bell, James O. Sickman,

Geology and Paleoclimatology Research

Rapid Communications in Mass SpectrometryVolume 28, Issue 5 p. 520-526 Research Article Correcting for background nitrate contamination in KCl-extracted samples during isotopic analysis of oxygen and nitrogen by the denitrifier method Michael D. Bell, Corresponding Author Michael D. Bell University of California, Riverside, Department of Botany and Plant Sciences, 900 University Avenue, Riverside, CA, 92521 USA Correspondence to: M. D. Bell, University of California, Riverside, Department of Botany and Plant Sciences, 900 University Avenue, Riverside, CA 92521, USA. E-mail: [email protected]Search for more papers by this authorJames O. Sickman, James O. Sickman University of California, Riverside, Department of Environmental Sciences, 900 University Avenue, Riverside, CA, 92521 USASearch for more papers by this author Michael D. Bell, Corresponding Author Michael D. Bell University of California, Riverside, Department of Botany and Plant Sciences, 900 University Avenue, Riverside, CA, 92521 USA Correspondence to: M. D. Bell, University of California, Riverside, Department of Botany and Plant Sciences, 900 University Avenue, Riverside, CA 92521, USA. E-mail: [email protected]Search for more papers by this authorJames O. Sickman, James O. Sickman University of California, Riverside, Department of Environmental Sciences, 900 University Avenue, Riverside, CA, 92521 USASearch for more papers by this author First published: 29 January 2014 https://doi.org/10.1002/rcm.6824Citations: 8Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Abstract RATIONALE Previous research has shown that the denitrifying bacteria Pseudomonas chlororaphis ssp. aureofaciens (P. aureofaciens) can be used to measure the δ15N and δ18O values of extracted soil nitrate (NO3–) by isotope ratio mass spectrometry. We discovered that N2O production from reference blanks made in 1 M KCl increased relative to blanks made of deionized water (DIW). Further investigation showed that isotopic standards made in KCl yielded δ15N and δ18O values different from the standards prepared in DIW. METHODS Three grades of crystalline KCl were dissolved in DIW to create solutions of increasing molarity (0.1 M to 2 M), which were added to P. aureofaciens broth and measured as blanks. Reference standards USGS-32, USGS-34, and USGS-35 were then dissolved in a range of KCl concentrations to measure isotopic responses to changing KCl molarity. Reference blanks and standards created in DIW were analyzed as controls to measure the impact of KCl on the δ15N and δ18O values. RESULTS The amount of N2O in the KCl blanks increased linearly with increasing molarity, but at different rates for each KCl grade. The isotopic values of the reference standards measured in KCl were systematically different from those measured in DIW, suggesting contamination by background NO3– in the KCl reagents. However, we also noted reduced conversion of NO3– into N2O as the KCl molarity increased, suggesting there is a physiological response of P. aureofaciens to KCl. CONCLUSIONS There is a small amount of NO3– present in crystalline KCl, which can bias isotopic measurement of NO3– at low sample concentrations. This can be minimized by making standards and blanks in the same KCl as is used in samples, diluting all samples and standards to the appropriate NO3– concentration using matched KCl solutions, and adding samples and standards to the broth at a constant volume to standardize the KCl molarity in the reaction vial. Copyright © 2014 John Wiley & Sons, Ltd. REFERENCES 1 C. M. Scrimgeour, D. Robinson, in Soil and Environmental Analysis Modern Instrumental Techniques, ( 3rd edn.), (Eds: K. A. Smith, M. S. Cresser). Marcel Dekker, New York, 2004. 2 C. Kendall, in Isotope Tracers in Catchment Hydrology, (Eds: C. Kendall, J. J. McDonnell). Elsevier Science B.V., Amsterdam, 1998. 3 R. Amundson, A. T. Austin, E. A. G. Schuur, K. Yoo, V. Matzek, C. Kendall, A. Uebersax, D. Brenner, W. T. Baisden. Global patterns of the isotopic composition of soil and plant nitrogen. Global Biogeochem. Cycles 2003, 17, 11. 4 D. A. Burns, C. Kendall. 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