How gut-stimulated denitrifiers influence soil N2O emission without earthworm activity

• Earthworm addition increased soil N2O flux both in sterilized and unsterilized soil.
• Cast addition did not change soil N2O and CO2 flux in unsterilized soil.
• Cast addition did not change soil N2O, but increased CO2 flux in sterilized soil.
• The separate effect of gut-stimulated denitrifiers on N2O emissions is not significant.

Gut-stimulated denitrifiers are responsible for the in vivo emission of N2O by earthworms, and contribute to the N2O that is emitted from certain terrestrial ecosystems. To evaluate the separate effect of gut-stimulated denitrifiers on N2O emissions, earthworms or their casts were inoculated into sterilized and unsterilized soil, respectively, and compared with control (soil without inoculation) in this study, to find out if there was a difference in N2O emissions during the 15 days incubation period. Compared with the control, earthworm inoculation significantly increased N2O flux and relative densities of nirS and narG gene copy numbers both in sterilized and unsterilized soil, while no significant difference was found when we transited and recolonized those gut-stimulated denitrifiers into soil artificially. In contrast, cast inoculation did not change CO2 emission in the unsterilized soil, but significant increased cumulative CO2 emission in the sterilized soil. Our data suggest that the effect of gut-stimulated denitrifiers on soil N2O produce was strongly diminished when separated from earthworm activity.