Recovery of nitrification and production of NO and N2O after exposure of soil to acetylene

Incubation of soil under low partial pressures of acetylene (10 Pa) is a widely used method to specifically inhibit nitrification due to the suicide inhibition of ammonium monooxygenase (AMO), the first enzyme in NH4+ oxidation by nitrifying bacteria. Although the inhibition of AMO is irreversible, recovery of activity is possible if new enzyme is synthesized. In experiments with three different soils, NH4+ concentrations decreased and NO; concentrations increased soon after acetylene was removed from the atmosphere. Recovery of NO production started immediately after the removal of acetylene. The release rates of NO and N2O were higher in soil samples which were only preincubated with 10 Pa acetylene than in those which were kept in the presence of 10 Pa acetylene. In the permanent presence of 10 Pa acetylene, NH4+ and NO3- concentrations stayed constant, and the release rates of NO and N2O were low. These low release rates were apparently due to processes other than nitrification. Our experiments showed that the blockage of nitrification by low (10 Pa) acetylene partial pressures is only reliable when the soil is kept in permanent contact with acetylene.