Respiration of nitrous oxide in suboxic soil

Summary Reduction of nitrous oxide (N 2 O) is an autonomous respiratory pathway. Nitrous oxide is an alternative electron acceptor to O 2 when intensive biological activity and reduced diffusivity result in an O 2 deficit. Hypoxic or anoxic micro sites may form even in well‐aerated soils, and provide a sink for N 2 O diffusing through the gas‐filled pore space. We reproduced similar in vitro conditions in suboxic (0.15% O 2 ) flow‐through incubation experiments with samples from a Stagnosol and from a Histosol. Apparent half‐saturation constants ( k m ) for N 2 O reduction were similar for both soils and were, on average, 3.8 μmol mol −1 at 5°C, 5.1 μmol mol −1 at 10°C, and 6.9 μmol mol −1 at 20°C. Respiration of N 2 O was estimated 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).