Cycloheximide inhibition of peptone-induced nitrate production across a soil moisture gradient

The antibiotic block technique is used to distinguish between fungal and bacterial induced activity. In the present study, the antibiotic inhibition of peptone-induced NO3- production was tested across a soil moisture gradient. Soil was incubated at 60, 80, 90 and 100% water-filled pore space (WFPS) and as a water slurry. Peptone was used as the substrate and cycloheximide and C2H2 (0.1% v/v) were added to inhibit fungal and autotrophic nitrification, respectively, the latter being considered mainly of bacterial origin. At all moisture contents is more than 80% of NO 3- production was due to autotrophic nitrification. At increasing water contents the percentage of NO3- production inhibited by C2H2 increased, whereas the percentage inhibited by cycloheximide decreased from 26.4% at 60% WFPS to 4.6% in the water slurry, suggesting a different sensitivity of bacterial and fungal nitrification to soil moisture. Although no direct evidence of an alteration in the fungal population was produced in this experiment, data proved that water content influences the result of the test and hence care should be taken when comparing data using different test conditions. © Springer-Verlag 2005.