No evidence that earthworms increase soil greenhouse gas emissions (CO 2 and N 2 O) in the presence of plants and soil moisture fluctuations

Earthworms can stimulate plant productivity, but their impact on soil greenhouse gases (GHG) is still debated. Methodological challenges of measuring GHG in experiments with plants are presumably contributing to the status quo, with the majority of studies being conducted without plants. Here we report the effect of earthworms (without, anecic, endogeic and their combination) and plants (with and without) on GHG (CO 2 and N 2 O) emissions in an experiment. N 2 O emissions were also 34.6 and 44.8% lower when both earthworm species and only endogeic species were present, respectively, while plants reduced the cumulative N 2 O emissions by 19.8%. No effects on CO 2 were found. Estimates of soil macroporosity measured by X-ray tomography show that the GHG emissions were mediated by their burrowing activity affecting the soil aeration and water status. Both GHG emissions decreased with the macropore volume in the top soil, presumably due to reduced moisture and microbial activity. N 2 O emissions also decreased with macropore volume in the deepest layer, likely caused by a reduction in anaerobic microsites. Our results indicate that, under experimental conditions allowing for plant and earthworm engineering effects on soil moisture, earthworms do not increase GHG emissions and that endogeic earthworms may even reduce N 2 O emissions.