SELECTIVE-INHIBITION OF AMMONIUM OXIDATION AND NITRIFICATION-LINKED N2O FORMATION BY METHYL-FLUORIDE AND DIMETHYL ETHER

Methyl fluoride (CH3F) and dimethyl ether (DME) inhibited nitrificatio n in washed-cell suspensions of Nitrosomonas europaea and in a variety of oxygenated soils and sediments. Headspace additions of CHF (10% v ol/vol!) and DME (25% vol/vol!) fully inhibited NO2- and N2O producti on from NH4+ in incubations of N. europaea, while lower concentrations of these gases resulted in partial inhibition. Oxidation of hydroxyla mine (NH2OH) by N. europaea and oxidation of NO2- by a Nitrobacter sp. were unaffected by CHF or DME. In nitrifying soils, CH3F and DME inhi bited N2O production. In field experiments with surface flux chambers and intact cores, CH3F reduced the release of N2O from soils to the at mosphere by 20- to 30-fold. Inhibition by CH3F also resulted in decrea sed NO3- + NO2- levels and increased NH4+ levels in soils. CH3F did no t affect patterns of dissimilatory nitrate reduction to ammonia in cel l suspensions of a nitrate-respiring bacterium, nor did it affect N2O metabolism in denitrifying soils. CHF and DME will be useful in discri minating N2O production via nitrification and denitrification when bot h processes occur and in decoupling these processes by blocking NO2- a nd NO3- production.