Short-Term Effects of Earthworms (Eisenia andrei) on Soil CO₂ Emission during Autumn in a Temperate Deciduous Forest

This study examined the short-term effects of earthworms on (1) soil CO₂ emissions from litter decomposition and (2) the soil factors in an oak-dominated temperate forest in Korea. Cylindrical containers with openings covered with mesh at the top and bottom were half-buried in the forest floor. The layout of the containers comprised three treatments—control (C: soil), litter (L: soil + litter), and litter with earthworms (LE: soil + litter + earthworms), using Salix alba leaf litter and Eisenia andrei earthworms. The headspace CO₂ concentrations and soil properties, including temperature and water content, were measured from October 7 to November 25, 2022. The mean soil CO₂ emissions in the C, L, and LE treatments were determined to be 2.5 ± 0.3, 3.0 ± 0.3, and 2.8 ± 0.2 g C m^− 2 day^− 1, respectively. CO₂ emissions in the LE treatment were initially the highest but subsequently declined and were surpassed by those in the C and L treatments. This decline may be attributed to reduced earthworm activity and an increase in earthworm mortality through decreasing soil temperatures, with an earthworm recovery rate of 36%. At the end of the study period, it appeared that earthworms did not contribute to soil CO₂ emissions through their direct activity and indirect microbial activation, but rather inhibited microbial activity. Soil CO₂ emissions were additionally negatively related with soil carbon and nitrogen concentrations. This study presented microbial activity being a prominent factor in soil CO₂ emissions. Further investigations into the microbial contribution and interaction with earthworms to organic matter decomposition are warranted.