Ammonia-oxidizing activity under extremely oligotrophic conditions in strongly acid tea soils

Abstract

The number and the activity of chemolithotrophic ammonia-oxidizing bacteria (CAB) in acid soils were determined and compared with those in neutral soils. Among the soils tested, CAB were predominant in acid tea soils but were not conspicuous in an acid grassland soil. In general, the activity decreased along with the net concentration of NH3 , suggesting that the major factor for CAB activity in acid soils was the substrate availability, regardless of the soil type and soil pH. In one of the acid tea soils tested, NO2 − was actively produced in a hundred-lower range of the net NH3 concentration, compared with other acid soils, and the activity increased sharply with a moderate increase in the NH3 concentration, presumably due to the high cell activity under oligotrophic conditions and not because of the abundance of CAB. A semi-quantitative analysis was carried out based on PCR and probing of the ammonia monooxygenase gene. It was suggested that CAB correlating to Nitrosomonas eutropha and Nitrosomonas sp. TK794 were predominant in the acid tea soils.