Metabolism of nitric oxide and nitrous oxide during nitrification and denitrification in soil at different incubation conditions

Abstract

NO production and consumption rates as well as N2O accumulation rates were measured in a loamy cambisol which was incubated under different conditions (i.e. soil moisture content, addition of nitrogen fertilizer and/or glucose, aerobic or anaerobic gas phase). Inhibition of nitrification with acetylene allowed us to distinguish between nitrification and denitrification as sources of NO and N2O. Under aerobic conditions untreated soil showed very low release of NO and N2O but high consumption of NO. Fertilization with NH4+ or urea stimulated both NO and N2O production by nitrification. Addition of glucose at high soil moisture contents led to increased N2 and N2O production by denitrification, but not to increased NO production rates. Anaerobic conditions, however, stimulated both NO and N2O production by denitrification. The production of NO and N2O was further stimulated at low moisture contents and after addition of glucose or NO3−. Anaerobic consumption of NO by denitrification followed Michaelis-Menten kinetics and was stimulated by addition of glucose and NO3−. Aerobic consumption of NO followed first-order kinetics up to mixing ratios of at least 14 ppmv NO, was inhibited by autoclaving but not by acetylene, and decreased with increasing soil moisture content. The high NO-consumption activity and the effects of soil moisture on the apparent rates of anaerobic and aerobic production and consumption of NO suggest that diffusional constraints have an important influence on the release of NO, and may be a reason for the different behaviour of NO release vs N2O release.