Burrowing activity of the earthworms Lumbricus terrestris and Aporrectodeagiardi and consequences on C transfers in soil

Two earthworms species, Lumbricus terrestris (epianecic) and Aporrectodea g iardi (anecic) were incubated in microcosms with an epigeic C-13-labelled l itter for 246 d. At the end of the experiment, different soil compartments (surface casts, walls and peripheries of burrows, and surrounding soil) wer e sampled for C-13 analysis. Two-dimensional images acquired using X-ray co mputed tomography allowed to estimate the weight of the 'burrow wall' and ' burrow periphery' compartments which are required to establish C balance. I n the case of L. terrestris, the formed structures were more C litter enric hed compared to the other species. The permanent character of the burrow sy stem could lead to a high and constant enrichment of the entire burrow syst em. As consequence, the percentage of C litter in the 'burrow wall' and 'bu rrow periphery' compartments was important in spite of their low volume. Th e denser system developed by A. giardi resulted in C litter dilution in the whole formed structures. The C litter enrichment decreased with the soil d epth, but owing to the intensity of the burrowing activity, the C litter tr ansfers into the 'burrow walls' and 'burrow periphery' were important and t he C Litter was homogeneously distributed throughout the whole column. (C) 2000 Editions scientifiques et medicales Elsevier SAS.