Impact of earthworm Lumbricus terrestris living sites on the greenhouse gas balance of no-till arable soil

Abstract. We studied the effect of the deep-burrowing earthworm Lumbricus terrestris on the greenhouse gas (GHG) fluxes and global warming potential (GWP) of arable no-till soil using both field measurements and a controlled 15-week laboratory experiment. In the field, the emissions of nitrous oxide (N₂O) and carbon dioxide (CO₂) were on average 43 and 32 % higher in areas occupied by L. terrestris (the presence judged by the surface midden) than in adjacent, unoccupied areas (with no midden). The fluxes of methane (CH₄) were variable and had no consistent difference between the midden and non-midden areas. Removing the midden did not affect soil N₂O and CO₂ emissions. The laboratory results were consistent with the field observations in that the emissions of N₂O and CO₂ were on average 27 and 13 % higher in mesocosms with than without L. terrestris. Higher emissions of N₂O were most likely due to the higher content of mineral nitrogen and soil moisture under the middens, whereas L. terrestris respiration fully explained the observed increase in CO₂ emissions in the laboratory. In the field, the significantly elevated macrofaunal densities in the vicinity of middens likely contributed to the higher emissions from areas occupied by L. terrestris. The activity of L. terrestris increased the GWP of field and laboratory soil by 50 and 18 %, but only 6 and 2 % of this increase was due to the enhanced N₂O emission. Our results suggest that high N₂O emissions commonly observed in no-till soils can partly be explained by the abundance of L. terrestris under no-till management and that L. terrestris can markedly regulate the climatic effects of different cultivation practises.