Sources of nitrous oxide production following wetting of dry soil

Abstract Production of N₂O was detected within 30 min of adding water to very dry soil (matric water potential < −9 MPa) sampled at the end of the dry season from an annual grassland of California, U.S.A. Using C₂H₂ to inhibit nitrification, we demonstrate that nitrification was a modest source of N₂O in sieved soil wetted to a water content below field capacity, but that denitrification was the major source of N₂O in sieved soils wetted to a water content above field capacity and in intact cores wetted either below or above field capacity. Significant abiological sources of N₂O were not detected. De novo enzyme synthesis began within 4–8 h of wetting, and denitrifying enzyme activity doubled within 26 h, indicating that denitrifying bacteria can quickly transform their metabolic state from adaptation to severe drought stress to rapid exploitation of changing resources.