Differential inhibition of nitrification by three metabolic inhibitors

In a soil slurry the effects of two uncouplers of oxidative phosphorylation, DNP (2,4 dinitrophenol) and CCCP (carbonyl cyanide m-chlorophenyl hydrazone), and one inhibitor of terminal oxidase (KCN) on biological oxidation (nitrification) of NH4+ and NO2- to NO3- were studied. DNP did not affect, KCN reduced, and CCCP fully inhibited the oxidation of both NH4+ and NO2- to NO3- Addition of DNP to soil slurry resulted in formation of excess NO3- (over that of the control) which was stoichiometrically close to the amount of nitrogen in the added DNP. It is suggested that the ineffectiveness of DNP as nitrification inhibitor was partly due to its rapid hydrolysis and formation of excess NO2- which was in turn nitrified to NO3-. It is concluded that in comparison to DNP, CCCP and KCN introduce no artefacts into the experimental cultures and are thus better suited for studies involving inhibition of biological nitrification than DNP.