Nitrifying populations and the destruction of nitrogen dioxide in soil

The nitrite formed from nitrogen dioxide (NO2) was oxidized more readily in soil that had been treated previously with the gas than in soil not so pre-exposed. The reaction was inhibited by 1.0 but not by 0.01 mM chlorate. The population of nitrite-oxidizing autotrophs estimated by the most-probable-number procedure was too small and often grew too late to account for oxidation of the nitrite generated from NO2. The reaction also proceeded in soil heated to 42° to 45°C or treated with 0.16 mM chlorate, although the countable autotrophs did not increase during the transformation or grew only late in the active period of nitrite oxidation. The data suggest that unknown populations are responsible for metabolism of the nitrite produced from NO2 entering soil.