Characterization of the burrow system of the earthworms Lumbricus terrestris and Aporrectodea giardi using X-ray computed tomography and image analysis

The burrow systems of two earthworm species (Lumbricus terrestris and Aporr ectodea giardi) were studied in artificially packed soil columns placed in controlled conditions in the laboratory. At the end of the incubation, whic h lasted 246 days, the burrow systems were characterized on the undisturbed columns using X-ray computed tomography. This method provided a set of dig itized images corresponding to horizontal 3-mm-thick sections. The followin g parameters were measured using image analysis on each section: number of biopores, their volume, and their individual orientation calculated using a n elliptical model of the earthworm channel. The profiles of these paramete rs through the columns showed that the burrow systems of L. terrestris and A. giardi, which are both anecic species, were very different in terms of t otal volume, number of burrows, burrow orientation and extension with soil depth. These results led us to conclude that the burrow system of L. terres tris can be considered as a permanent structure whereas that of A. giardi i s closer to the burrow system of endogeic species.