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.

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 15 N-ammonium isotopic pool dilution techniques and combined with acetylene (C 2 H 2 , 10 Pa) as a specific inhibitor of autotrophic nitrification and sodium chlorate (NaClO 3 ) as a potential inhibitor of heterotrophic nitrification. Additionally, CO 2 , N 2 O and CH 4 fluxes were measured to identify potential side-effects of inhibitors on soil respiration and CH 4 fluxes. The presence of C 2 H 2 completely eliminated gross nitrification in all investigated soil samples. The addition of NaClO 3 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 NaClO 3 decreased net CH 4 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. [ABSTRACT FROM AUTHOR]