Burrow systems made by Aporrectodea nocturna and Allolobophora chlorotica in artificial cores: morphological differences and effects of interspecific interactions

Abstract

Burrow systems of earthworms contained in artificial cores were analysed through X-ray computed tomography and 3D skeleton reconstructions. Gas diffusion experiments were carried out on these cores to characterize soil transfer properties associated with the different burrow systems. Three types of cores were studied: cores in which Aporrectodea nocturna, an anecic earthworm was introduced (treatment 1), cores in which Allolobophora chlorotica, an endogeic earthworm was introduced (treatment 2) and cores that contained both species (treatment 3). Comparisons of the characteristics of the burrow systems of treatment 1 and 2 show important differences: the burrow system of A. nocturna comprises fewer burrows, which are longer, less branched, more vertical and have a lower sinuosity. The burrow system of A. chlorotica is characterized by lower continuity, which however did not result in a lower soil diffusivity. To study the burrow systems made by the two species in the same core (treatment 3), a separation that was based on differences in pore diameter between the two species and that takes into account the burrow orientation was designed. This separation was proven to be efficient since it resulted in low percentages of errors (around 10%) when applied to the burrow systems of treatments 1 and 2. Comparison of the burrow systems from treatments 1 and 3 demonstrated that the burrow system of A. nocturna was influenced by the presence of A. chlorotica: in treatment 3, A. nocturna made burrows that were smaller, more vertical and less branched. However, these interactions have to be confirmed under natural conditions.