Isotopologue fractionation during microbial reduction of N2O within soil mesocosms as a function of water-filled pore space

Estimation of isotopologue variation of N<sub>2</sub>O during denitrification by <i>Pseudomonas aureofaciens</i> and <i>Pseudomonas</i> chlororaphis: Implications for N<sub>2</sub>O source apportionment

“…The non-linear behaviour indicates that the fractionation factor, , is not constant, a phenomenon not unexpected for multi-step reactions in which more than one 25 enzymatic step and diffusion of products and/or substrates into and out of the cell can result in variation in isotopic discrimination (Granger et al, 2008;Sutka et al, 2008). Because the fractionation factor varies during multi-step reactions, it is best considered a net isotope effect (η) (Jinuntuya-Nortman et al, 2008). The reduction of NO3 -to N2O during denitrification involves three enzymes and multiple opportunities for diffusion, all cases where isotope discrimination can occur ( Figure 5).…”

“…These oxygen exchange effects are difficult to quantify making interpretation of η 18 O data difficult. to the relative importance of diffusion and enzymatic fractionation in controlling η. Fractionation associated with enzymes is often much larger than that associated with diffusion, and enzymatic fractionation is fully expressed when diffusion does not limit substrate supply to the enzyme (Jinuntuya-Nortman et al, 2008;Ostrom and Ostrom, 2012). Thus, the largest η is 15 expected at the beginning of the reaction, consistent with what we observed.…”

“…The term net isotope effect (η) has been used to describe isotopic 15 discrimination, the change in isotope value, observed during a multi-step reaction (Jinuntuya-Nortman et al, 2008). Therefore, η is equivalent to y´ in Eq.…”

“…Apportionment approaches require that the isotope 20 values of N2O differ between the two production processes and remain constant throughout the course of a reaction (JinuntuyaNortman et al, 2008;Ostrom and Ostrom, 2017). However, shifts or fractionation in the isotope values of N2O produced during either nitrification or denitrification can compromise source apportionment (Barford et al, 1999;Perez et al, 2000;Sutka et al, 2008;Yoshida, 1988), and reduction of N2O by denitrification may further alter isotope values (Jinuntuya-Nortman et al, 2008 alternative tool for apportionment of N2O production (Yoshida and Toyoda, 2000). The large difference in SP of N2O produced from nitrification and denitrification (ca.…”

Using stable isotopes to follow excreta N dynamics and N2O emissions in animal production systems

“…The isotopomer analyses of N 2 O have been applied to examine the effects of various treatments on N 2 O production and consumption including: biogas residue application to soil (Koster et al, 2011), cropping soils receiving organic and synthetic fertilisers (Toyoda et al, 2011), comparisons of tropical forest and cropping soils (Park et al, 2011), soil moisture conditions (Well et al, 2006;Jinuntuya-Nortman et al, 2008;Bergstermann et al, 2011), composting (Maeda et al, 2010), stimulated soil denitrification using glucose (Meijide et al, 2010), cultivation of temperate grassland (Ostrom et al, 2010), microbial processes (Bol et al, 2003;Toyoda et al, 2005;Perez et al, 2006;Sutka et al, 2006;Well et al, 2008), the effect of ruminant diet on subsequent slurry N 2 O fluxes (Cardenas et al, 2007) and ruminant urine (Yamulki et al, 2001). Most of these early studies were of short duration and had limited temporal sampling.…”