Respiration of nitrous oxide in suboxic soil

Reduction of nitrous oxide (N2O) is an autonomous respiratory pathway. Nitrous oxide is an alternativeelectron acceptor to O2 when intensive biological activity and reduced diffusivity result in an O2 deficit.Hypoxic or anoxic micro sites may form even in well-aerated soils, and provide a sink for N2O diffusingthrough the gas-filled pore space. We reproduced similar in vitro conditions in suboxic (0.15% O2)flow-through incubation experiments with samples from a Stagnosol and from a Histosol. Apparenthalf-saturation constants (km) for N2O reduction were similar for both soils and were, on average,3.8 mmol mol1 at 5°C, 5.1 mmol mol1 at 10°C, and 6.9 mmol mol1 at 20°C. Respiration of N2O wasestimated to contribute a maximum proportion of 1.7% to total respiration in the Stagnosol (pH 7.0)and 0.9% in the Histosol (pH 2.9).