ABSTRACTEarthworm activity is known to increase emissions of nitrous oxide (N2O) 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 N2O 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 N2O emissions from the soil. We set up a 90-day mesocosm experiment in which15N-labeled maize (Zea maysL.) was either mixed in or applied on top of the soil in the presence or absence of the epigeic earthwormLumbricus rubellusand/or the endogeic earthwormAporrectodea caliginosa. We measured N2O fluxes and tested the bulk soil for denitrification enzyme activity and the abundance of 16S rRNA and denitrifier genesnirSandnosZthrough real-time quantitative PCR. Compared to the control,L. rubellusincreased denitrification enzyme activity and N2O emissions on days 21 and 90 (day 21,P= 0.034 andP= 0.002, respectively; day 90,P= 0.001 andP= 0.007, respectively), as well as cumulative N2O emissions (76%;P= 0.014).A. caliginosaactivity led to a transient increase of N2O emissions on days 8 to 18 of the experiment. Abundance ofnosZwas significantly increased (100%) on day 90 in the treatment mixture containingL. rubellusalone. We conclude thatL. rubellusincreased cumulative N2O emissions by affecting denitrifier community activity via incorporation of fresh residue into the soil and supplying a steady, labile carbon source.
Association of Earthworm-Denitrifier Interactions with Increased Emission of Nitrous Oxide from Soil Mesocosms Amended with Crop Residue
