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 p roduction in slurries of calcareous silt loam and river bank sediment at different oxygen concentrations was determined using acetylene as n itrification inhibitor. The addition of 10 Pa acetylene resulted in in hibition of nitrous oxide production at oxic conditions, but strongly enhanced the nitrous oxide production at oxygen-poor and anoxic condit ions. Inhibition of nitrification by short exposure (1 to 24 h) to hig h concentrations of acetylene (100 Pa to 10 kPa) was tested using the same samples. After the removal of acetylene, nitrification was inhibi ted 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 ni trate-rich microsites and that the method was suitable for assessing t he nitrifier contribution to the nitrous oxide emission of intact soil and sediment cores.