期刊
ECOLOGICAL INDICATORS
卷 126, 期 -, 页码 -出版社
ELSEVIER
DOI: 10.1016/j.ecolind.2021.107639
关键词
REOX/MIMS; (NO3-)-N-15; Gross nitrification; Gross NO3- immobilization; Isotope dilution method
资金
- Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology (Qingdao) [2018SDKJ04064]
- National Natural Science Foundation of China [42001088, 41976128]
- Basic Research and Applied Basic Research of Guangdong Province of China [2019A1515110794]
- China Postdoctoral Science Foundation [2019M653151]
- Fundamental Research Funds for the Central Universities [19lgpy93, 181gzd07]
The developed REOX/MIMS method provides a sensitive and precise approach for quantifying (NO3-)-N-15 concentrations in small water volumes. It was rapid, accurate, and cost-effective, making it a valuable tool for studying N transformation rates in isotope-enrichment experiments in various ecosystems.
Using N-15 stable isotope as a tracer to quantify N transformation rates in isotope-enrichment experiments improves understanding of the N cycle in various ecosystems. However, measuring N-15-nitrate ((NO3-)-N-15) in small volumes of water for these experiments is a major challenge due to the inconvenience of preparing samples by traditional techniques. We developed a REOX/MIMS method by applying membrane inlet mass spectrometry (MIMS) to determining (NO3-)-N-15 concentrations in a small volumes of water from isotope-enrichment experiments after converting the dissolved inorganic N to N-2. The nitrates (NO3- + NO2-) were reduced to NH4+ with zinc powder, and the ammonium (NH4+) was then oxidized to N-2 by hypobromite iodine solution. The resulting N-29(2) and N-30(2) were measured via MIMS. This optimized protocol provides a sensitive (similar to 0.1 mu M) and precise (relative standard deviation = 0.1-4.37%) approach to quantify (NO3-)-N-15 concentrations (0.1-500 mu M) in water samples over a wide range of salinities (0-35%) and in 2 M KCl solution with excellent calibration curves (R-2 >= 0.9996, p < 0.0001). The method was combined with (NO3-)-N-15 isotope-enrichment incubation experiments to measure gross nitrification and gross NO3- immobilization rates in various ecosystems. It was rapid, accurate, and cost-effective. Future applications of this efficient approach will inform scientists, modelers and decision makers about mechanisms, sources, fates, and effects of NO3 delivered to or produced in numerous aquatic and terrestrial ecosystems.
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