Abstract
<jats:p>Nitrogen isotope kinetic fractionation factors were carefully studied and determined for 2 the production and consumption processes of the microbiological nitrate reduction system. Two 3 species of denitrifying bacteria were incubated under several concentrations of nitrate and 4 nitrous oxide (N2O), the thirdly important greenhouse gases and most effective ozone layer 5 regulation in the stratosphere. The kinetic nitrogen isotope fractionation factor for NO3- → 6 N2O was 0.963–0.967 and was not strongly influenced by the NO3- concentration over the 7 range 10-3–10-1 M, whereas the fractionation factor for N2O → N2 was 0.974–0.995 and was 8 influenced by the partial pressure of N2O over the range 0.33–0.01 atm. Although the present 9 results were estimated through in vitro simulation, and N2O reduction may occur in vivo, 10 fractionation for N2O → N2 is likely not significant under naturally occurring conditions in 11 which the partial pressure of N2O is much lower than the present experimental conditions.</jats:p>