Inhibitory and side effects of acetylene (C2H2) and sodium chlorate (NaClO3) on gross nitrification, gross ammonification and soil-atmosphere exchange of N2O and CH4 in acidic to neutral montane grassland soil

• C2H2 completely eliminated gross nitrification in the investigated soils.
• NaClO3 had no effect on gross nitrification.
• C2H2 effectively blocks the oxidation of ammonia.
• Low concentrations of C2H2 effectively inhibited net CH4 uptake in soil.

Nitrification is a central component of the terrestrial nitrogen (N) cycle, but the contribution of autotrophic and heterotrophic nitrification to total gross nitrification remains poorly understood. To clarify their relative importance in neutral and moderate acid soils, an incubation experiment was conducted with 15N-ammonium isotopic pool dilution techniques and combined with acetylene (C2H2, 10 Pa) as a specific inhibitor of autotrophic nitrification and sodium chlorate (NaClO3) as a potential inhibitor of heterotrophic nitrification. Additionally, CO2, N2O and CH4 fluxes were measured to identify potential side-effects of inhibitors on soil respiration and CH4 fluxes.The presence of C2H2 completely eliminated gross nitrification in all investigated soil samples. The addition of NaClO3 affected neither gross nitrification nor gross ammonification in soils of both investigated grassland sites. This provided strong evidence that heterotrophic nitrification was not an important process in the investigated grassland soils. Acetylene but not NaClO3 decreased net CH4 uptake, likely due to homology of the enzymes ammonia monooxygenase. Overall, the present study shows a dominant role of autotrophic nitrification in gross nitrate production for both neutral and slightly acid soils and illustrates the potential of acetylene as an inhibitor of gross autotrophic nitrification.