Stable isotope discrimination during soil denitrification: Production and consumption of nitrous oxide

Abstract

Measuring the stable isotope composition of nitrous oxide (N2O) evolved from soil could improve our understanding of the relative contributions of the main microbial processes (nitrification and denitrification) responsible for N2O formation in soil. However, interpretation of the isotopic data in N2O is complicated by the lack of knowledge of fractionation parameters by different microbial processes responsible for N2O production and consumption. Here we report isotopic enrichment for both nitrogen and oxygen isotopes in two stages of denitrification, N2O production and N2O reduction. We found that during both N2O production and reduction, enrichments were higher for oxygen than nitrogen. For both elements, enrichments were larger for N2O production stage than for N2O reduction. During gross N2O production, the ratio of δ18O‐to‐δ15N differed between soils, ranging from 1.6 to 2.7. By contrast, during N2O reduction, we observed a constant ratio of δ18O‐to‐δ15N with a value near 2.5. If general, this ratio could be used to estimate the proportion of N2O being reduced in the soil before escaping into the atmosphere. Because N2O‐reductase enriches N2O in both isotopes, the global reduction of N2O consumption by soil may contribute to the globally observed isotopic depletion of atmospheric N2O.

Evidence for the predominance of denitrification as a source of N2O in temperate agricultural soils based on isotopologue measurements

“…Using the flux-weighted average d 15 N for soil NO 3 À at KBS of 2.5% [Ostrom et al, 1998] to represent the nitrogen isotope value of the substrate, the NIE for our data, 7 to À19%, falls within or above the range of values indicative of N 2 O production from denitrification (À13 to À28%). However, like Perez et al [2001] [Menyailo and Hungate, 2006;Ostrom et al, 2007;Sutka et al, 2008;Vieten et al, 2007;JinuntuyaNortman et al, 2008]. Variation in a fractionation factor can result from changes in the relative importance of the reaction rate, constants for diffusion and enzymatic reduction that occur during an experiment [Jinuntuya-Nortman et al, 2008;Sutka et al, 2008].…”

Continuous measurements of nitrous oxide isotopomers during incubation experiments

“…(3). Equation (3) is valid for the bulk 15 N / 14 N isotope ratios of N 2 O (δ 15 N bulk ) and for both of the two isotopomer isotope ratios (δ 15 N α and δ 15 N β ) (Mariotti et al, 1981;Menyailo and Hungate, 2006;Ostrom et al, 2007;Lewicka-Szczebak et al, 2014). …”

Can N2O stable isotopes and isotopomers be useful tools to characterize sources and microbial pathways of N2O production and consumption in tropical soils?

“…References: a, [Sutka et al, 2006;Ueda et al, 1999;Yoshida et al, 1984]; b, [Pérez et al, 2006]; c, [Barford et al, 1999;Snider et al, 2008;Sutka et al, 2006;Thompson et al, 2004;Toyoda et al, 2005;Yoshida et al, 1984]; d, [Mariotti et al, 1981[Mariotti et al, , 1982Menyailo and Hungate, 2006;Ostrom et al, 2007;Pérez et al, 2006;Snider et al, 2008;Wada et al, 1991;Well et al, 2006]; e, [Barford et al, 1999;Ostrom et al, 2007;Thompson et al, 2004;Wahlen and Yoshinari, 1985;Webster and Hopkins, 1996;Yoshida et al, 1984]; f, [Mandernack et al, 2000;Menyailo and Hungate, 2006;Ostrom et al, 2007;Vieten et al, 2007]; g, [Sutka et al, 2003[Sutka et al, , 2004.…”

“…Thus, " a /" 18 = +1.6 ± 0.3. We must next make the assumption that an average value for " 18 of ∼−15‰ for the reduction of N 2 O [Menyailo and Hungate, 2006;Ostrom et al, 2007;Vieten et al, 2007] is relevant for the soils of this study (at least for the sake of our back of the envelope calculation here). Thus, we derive a value for " a of −24‰.…”