Influence of 15N enrichment on the net isotopic fractionation factor during the reduction of nitrate to nitrous oxide in soil.
Nitrous oxide, a greenhouse gas, is mainly emitted from soils during the denitrification process. Nitrogen stable-isotope investigations can help to characterise the N(2)O source and N(2)O production mechanisms. The stable-isotope approach is increasingly used with (15)N natural abundance or relatively low (15)N enrichment levels and requires a good knowledge of the isotopic fractionation effect inherent to this biological mechanism. This paper reports the measurement of the net and instantaneous isotopic fractionation factor (alpha(s/p) (i)) during the denitrification of NO(3) (-) to N(2)O over a range of (15)N substrate enrichments (0.37 to 1.00 atom% (15)N). At natural abundance level, the isotopic fractionation effect reported falls well within the range of data previously observed. For (15)N-enriched substrate, the value of alpha(s/p) (i) was not constant and decreased from 1.024 to 1.013, as a direct function of the isotopic enrichment of the labelled nitrate added. However, for enrichment greater than 0.6 atom% (15)N, the value of alpha(s/p) (i) seems to be independent of substrate isotopic enrichment. These results suggest that for isotopic experiments applied to N(2)O emissions, the use of low (15)N-enriched tracers around 1.00 atom% (15)N is valid. At this enrichment level, the isotopic effect appears negligible in comparison with the enrichment of the substrate.
Mathieu
Olivier
O
UMR 1229 Microbiologie et Géochimie des Sols, Université de Bourgogne, UFR des Sciences de la Terre et de l'Environnement, 6 boulevard Gabriel, 21000 Dijon, France. olivier.mathieu@u-bourgogne.fr
Lévêque
Jean
J
Hénault
Catherine
C
Ambus
Per
P
Milloux
Marie-Jeanne
MJ
Andreux
Francis
F
D005591:Chemical Fractionation; D008401:Gas Chromatography-Mass Spectrometry; D009566:Nitrates / Q000737:chemistry*; D009587:Nitrogen Isotopes / Q000737:chemistry*; D009609:Nitrous Oxide / Q000737:chemistry*; D010084:Oxidation-Reduction; D012987:Soil; D012989:Soil Pollutants / Q000737:chemistry*
D009566:Nitrates; D009587:Nitrogen Isotopes; D012987:Soil; D012989:Soil Pollutants; D009609:Nitrous Oxide