Short exposure to acetylene to distinguish between nitrifier and denitrifier nitrous oxide production in soil and sediment samples

The contribution of nitrifiers and denitrifiers to the nitrous oxide production in slurries of calcareous silt loam and river bank sediment at different oxygen concentrations was determined using acetylene as nitrification inhibitor. The addition of 10 Pa acetylene resulted in inhibition of nitrous oxide production at oxic conditions, but strongly enhanced the nitrous oxide production at oxygen-poor and anoxic conditions. Inhibition of nitrification by short exposure (1 to 24 h) to high concentrations of acetylene (100 Pa to 10 kPa) was tested using the same samples. After the removal of acetylene, nitrification was inhibited almost completely (82% to 89%) for at least 6 days whereas nitrous oxide reduction was restored within a day. It was concluded that the 'short exposure' inhibition method resulted in adequate nitrification inhibition without repressing the nitrous oxide reduction in anoxic nitrate-rich microsites and that the method was suitable for assessing the nitrifier contribution to the nitrous oxide emission of intact soil and sediment cores. [KEYWORDS: nitrous oxide emission; nitrification; denitrification; soil; sediment Nitrification; inhibition; inactivation; reduction; oxidation;bacteria; n2o]