Fractionation factors for stable isotopes of N and O during N₂O reduction in soil depend on reaction rate constant

B. Vieten, T. Blunier, A. Neftel, C. Alewell, and F. Conen
Rapid Communications in Mass Spectrometry, 21, 846-850 (PR, CO)

ABSTRACT.
Nitrous oxide (N₂O) is a major greenhouse gas that is mainly produced but also reduced by microorganisms in soils. We determined factors for N and O isotope fractionation during the reduction of N₂O to N₂ in soil in a flow-through incubation experiment. The absolute value of the fractionation factors decreased with increasing reaction rate constant. Reaction rates constants ranged from 1.7 10^-4 s^-1 to 4.5 10^-3 s^-1. The minimum, maximum and median of the observed fractionation factors were for N -36.0‰, -1.0‰ and -9.3‰ and for O -74.0‰, -6.9‰ and -26.3‰, respectively. The ratio of O isotope fractionation to N isotope fractionation was 2.4±0.3 and it was independent from the reaction rate constants. This leads us to conclude that fractionation factors are variables while their ratio in this particular reaction might be a constant.