Analysis of the C2H2 inhibition-based N2O production curve to characterize the N2O-reducing activity of denitrifying communities in soil

The characterization of an C2H2 inhibition-based N2O production curve was conducted to estimate the N2O-reducing activity of denitrifying communities in soil. By normalizing the N2O production curve and calculating the value of the area under the curve (AUC), visual differences in the time course of N2O production in the presence and absence of an C2H2 treatment were quantified in a series of experiments. The effects of liming and the addition of selected inorganic salts on the N2O-reducing activity of soil were analyzed. The average N2O/N2 + N2O ratio, which is the ratio of the AUC value in the absence and presence of C2H2, indicated that a declining pH and the addition of Cl− and Ca2+ resulted in the inhibition of the N2O-reducing activity, whereas liming (pH 6 using calcined lime, dolomite, charcoal, and ash of the charcoal) and SO42− and Mg2+ addition resulted in enhancing the N2O-reducing activity. Since the charcoal addition resulted in lowering the average N2O/N2 + N2O ratio despite the fact that charcoal contained larger amounts of Cl− and Ca2+ than SO42− and Mg2+, the alkalinity of the charcoal (pH 9.3) rather than the types of anions and cations may be the most significant factor in the stimulation of the N2O-reducing activity. In addition, we found a non-linear negative relationship between the average N2O/N2 + N2O ratios and the specific increasing rate constant of the N2O production curve. This result indicated that the application of a growth inhibitor of denitrifying communities into soil decreases the N2O-reducing activity of soil.