Soil CO2 flux affected by Aporrectodea caliginosa earthworms

The effects of Aporrectodea caliginosa earthworms on both carbon dioxide (CO₂) accumulation in and emissions from soil, as well as the simultaneous impact of earthworms on soil microbiological properties were investigated in a microcosm experiment carried out over 5.5 months. Concentration of CO₂ in soil air was greater at a depth of 15 cm when compared with a depth of 5 cm, but varied during the season both in control and earthworm-inhabited chambers. Peaks of CO₂ concentrations at both depths occurred in both treatments during August, approximately 80 days after the experiment started. Generally, the presence of earthworms increased the CO₂ concentration at 15-cm depth. Larger CO₂ emissions were consistently recorded in conjunction with higher amounts of CO₂ in soil air when chambers were inhabited by earthworms. The total CO₂ emissions during the experimental period covering 161 days were estimated at 118 g CO₂-C m⁻² and 99 g CO₂-C m⁻² from chambers with and without earthworms respectively. Moreover, the presence of earthworms increased microbial biomass in the centre and at the bottom of chambers, and enhanced both dehydrogenase activity and nitrifying enzyme activity in the soils. We suggest that the effect of earthworms on both the enhanced soil accumulation of CO₂ as well as emissions of CO₂ was mostly indirect, due to the impacts of earthworms on soil microbial community.