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Abstract

In model experiments under defined conditions (80%WHC, 300 mu g nitrate-N g(-1) dry soil, 30 degrees C) the effect of pO(2), pH and addition of easily decomposable organic matter on nitrous oxide production by Streptomyces nitrosporeus DSM 40023 from a sterilized sandy loam soil was studied. This streptomycete reduces nitrate to N2O but not to N-2. The strain was inoculated into a sterilized sandy loam sail (pH 6), enriched with nitrate and incubated at approximately 20 and 10% (v/v) O-2 for 26 days. In another series of experiments the pH was increased with NaOH-solution up to pH 7 or the soil was enriched with pulverized leaves (1%) to increase mineralization activity and the demand for electron accepters. In the headspace the concentration of O-2, CO2 and N2O was analysed by GC. The soil concentration of NO3-, NO2- and NH4+ was measured as well as the pH value. The population density was determined by the plate count method. At a decreased oxygen concentration of about 2.5% (v/v) in the headspace, S. nitrosporeus increased the release of N2O. In the experiments with an initial oxygen concentration of approximately 20% (v/v) this threshold of about 2.5%/(v/v) O-2 was hardly reached and consequently only little N2O was produced. Apparently, S. nitrosporeus uses O-2 in preference to nitrate, which is characteristical of nitrate respiration. A pH increase from pH 6 to 7 reduced the lag phase significantly and increased the rate of oxygen consumption, CO2 release and N2O production. Maximum nitrous oxide production was reached after 13 days. The result indicated that streptomycetes Like S. nitrosporeus may use nitrate, rate alternativly to O-2 to maintain energy conservation (ATP synthesis) with the release of N2O. So far, nothing is known about the role of streptomycetes in contributing to N2O production in natural soils.