Earthworm activity is known to increase emissions of nitrous oxide (N 2 O) from arable soils. Earthworm gut, casts, and burrows have exhibited higher denitrification activities than the bulk soil, implicating priming of denitrifying organisms as a possible mechanism for this effect. Furthermore, the earthworm feeding strategy may drive N 2 O emissions, as it determines access to fresh organic matter for denitrification. Here, we determined whether interactions between earthworm feeding strategy and the soil denitrifier community can predict N 2 O emissions from the soil. We set up a 90-day mesocosm experiment in which 15 N-labeled maize (Zea mays L.) was either mixed in or applied on top of the soil in the presence or absence of the epigeic earthworm Lumbricus rubellus and/or the endogeic earthworm Aporrectodea caliginosa. We measured N 2 O fluxes and tested the bulk soil for denitrification enzyme activity and the abundance of 16S rRNA and denitrifier genes nirS and nosZ through real-time quantitative PCR. Compared to the control, L. rubellus increased denitrification enzyme activity and N 2 O emissions on days 21 and 90 (day 21, P ‫؍‬ 0.034 and P ‫؍‬ 0.002, respectively; day 90, P ‫؍‬ 0.001 and P ‫؍‬ 0.007, respectively), as well as cumulative N 2 O emissions (76%; P ‫؍‬ 0.014). A. caliginosa activity led to a transient increase of N 2 O emissions on days 8 to 18 of the experiment. Abundance of nosZ was significantly increased (100%) on day 90 in the treatment mixture containing L. rubellus alone. We conclude that L. rubellus increased cumulative N 2 O emissions by affecting denitrifier community activity via incorporation of fresh residue into the soil and supplying a steady, labile carbon source.

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