PRODUCTION OF NO AND N2O BY PURE CULTURES OF NITRIFYING AND DENITRIFYING BACTERIA DURING CHANGES IN AERATION

Peak emissions of NO and N2O are often observed after wetting of soil, The reactions to sudden changes in the aeration of cultures of nitrif ying and denitrifying bacteria with respect to NO and N2O emissions we re compared to obtain more information about the microbiological aspec ts of peak emissions. In continuous culture, the nitrifier Nitrosomona s europaea and the denitrifiers Alcaligenes eutrophus and Pseudomonas stutzeri were cultured at different levels of aeration (80 to 0% air s aturation) and subjected to changes in aeration, The relative producti on of NO and N2O by N. ercr-opaea, as a percentage of the ammonium con version, increased from 0.87 and 0.17%, respectively, at 80% air satur ation to 2.32 and 0.78%, respectively, at 1% air saturation, At 0% air saturation, ammonium oxidation and N2O production ceased but NO produ ction was enhanced. Coculturing of N. europaea with the nitrite oxidiz er Nitrobacter winogranskyi strongly reduced the relative levels of NO and N2O production, probably as an effect of the lowered nitrite conc entration, After lowering the aeration, N. europaea produced large sho rt-lasting peaks of NO and N2O emissions in the presence but not in th e absence of nitrite, A. eutrophus and P. stutzeri began to denitrify below 1% air saturation, with the former accumulating nitrite and N2O and the latter reducing nitrate almost completely to N-2, Transition o f A. eutrophus and P. stutzeri from 80 to 0% air saturation resulted i n transient maxima of denitrification intermediates, Such transient ma xima were not observed after transition from 1 to 0%, Reduction of nit rate by A. euhophus continued 48 h after the onset of the aeration, wh ereas N2O emission by P, stutzeri increased for only a short period. I t was concluded that only in the presence of nitrite are nitrifiers ab le to dominate the NO and N2O emissions of soils shortly after a rainf all event.