Dynamics of reduction enzymes involved in the denitrification process in pasture soil

When oxygen is depleted in soil, reduction enzymes involved in the denitrification process are activated and de novo synthesis of enzymes starts within a few hours. The dynamics of these enzymes and the effect on the concentration of inorganic N formed were investigated for a soil from permanent pasture. Soil was incubated aerobically for 5 days and then amended with 100 mg NO3−-N kg−1. Treatments were with or without C2H2 and with or without chloramphenicol (found to inhibit de novo synthesis of reduction enzymes), purged of all O2, shaken and anaerobically incubated for 48 h while CO2 and N2O production and no3− and NO2− concentrations were monitored. Chloramphenicol was found to have no inhibitory effects on nitrate reduction indicating that nitrate reductase activity persisted in the absence of de novo synthesis. The persistence of nitrite reductase and nitrous oxide reductase was lower as the application of chloramphenicol increased NO2− concentrations and reduced N2 production. In the absence of chloramphenicol, de novo synthesis of nitrite reductase started 5 h and that of nitrous oxide 16 h after anaerobiosis was imposed. It is concluded that the dynamics of nitrite reductase have only a small effect on the N2O production as NO2− concentrations remained below l mg N kg−1 but the low persistence of N2O reductase in combination with its retarded de-repression results in a high N2O-to-N2 ratio when anaerobic conditions are rapidly induced.