Interactions between earthworm species in artificial soil cores assessed through the 3D reconstruction of the burrow systems

Abstract

The aim of this study was to determine the impact of the interactions between different earthworm species on the individual burrowing activity and especially on the characteristics of burrow systems. Towards this end, individuals of different earthworm species ( Lumbricus terrestris, Aporrectodea giardi, A. caliginosa) were inoculated as single or paired species treatments into artificially packed soil columns. After 8 months, the soil columns were scanned by X-ray computed tomography. Three-dimensional skeletons of the burrow systems were then computed to characterise the burrow systems (burrow number, total and mean burrowed length, segment distribution in relation to depth, and rate of branching). Pronounced differences between species were found. L. terrestris built a permanent burrow system characterised by low burrowed length, few connections and low rate of branching. On the contrary, A. giardi and A. caliginosa dug temporary burrow systems. The burrow system of A. giardi was the most interconnected and showed the highest total and mean burrowed lengths. Differences observed between single and paired species treatments mainly concerned the distribution of the burrow system in relation to soil depth in the core and total burrowed length. The burrow system of L. terrestris was much less deep and showed a higher length when the species was incubated together with A. caliginosa. The burrow system of A. caliginosa was much deeper when the worm was cultivated with A. giardi. Differences in the rate of branching were also shown in paired species treatments compared to single species treatments.