Inter- and intra-specific interactions of Lumbricus rubellus (Hoffmeister, 1843) and Octolasion lacteum (Örley, 1881) (Lumbricidae) and the implication for C cycling

Abstract Earthworms are important engineering species of many terrestrial ecosystems as they play a significant role in regulating C turnover. The effects of earthworms on moderating C decomposition processes differ across species and with interactions between species, which is not fully understood. We carried out an experiment to study the interactions of Lumbricus rubellus and Octolasion lacteum , and their effects on soil respiration. Laboratory mesocosms were set up using tulip poplar ( Liriodendron tulipifera) leaf litter and varying densities of earthworms in single and combined species treatments. CO 2 efflux rate was used as an indicator of C decomposition rates, and measured with CO 2 sensors every five days over one month. L. rubellus induced higher leaf consumption rate and higher CO 2 efflux than O. lacteum ; meanwhile O. lacteum grew more than L. rubellus . Both litter consumption rate and growth rate of earthworms decreased with increasing earthworm density. Soil CO 2 efflux increased with increasing earthworm density (from ∼1–2 μg CO 2  g −1  hr −1 with no earthworms to ∼ 4 μg CO 2  g −1  hr −1 with 8 earthworms). Combining the two species had a synergistic effect on leaf litter consumption, and neutralizing effects on soil respiration. The data suggest that the strength of intra- and inter-specific interactions among earthworm ecological groups varies at different absolute and relative densities, leading to altered leaf litter decomposition and C cycling.