The drilosphere concept: Fine-scale incorporation of surface residue-derived N and C around natural Lumbricus terrestris burrows

Anecic (deep-burrowing) earthworms are important for soil biogeochemical functioning, but the fine-scale spatial range at which they incorporate C and N around their burrows (the drilosphere sensu stricto) needs to be investigated under realistic conditions. We conducted a field experiment to delimit spatially the extent to which soil around natural Lumbricus terrestris burrows is influenced biochemically. We placed plant litter dual-labelled with C-13 and N-15 stable isotope tracers on L terrestris burrow openings and we measured residue-derived C-13 and N-15 in thin concentric layers (0-2, 2-4, 4-8 mm) around burrows with or without a resident earthworm. After 45 days, earthworms were significantly enriched in C-13 and N-15 as a result of feeding on the plant litter. At 0-5 cm soil depth, soil N-15 concentrations were significantly higher around occupied than unoccupied burrows, and they were significantly higher in all burrow layers (including 4-8 mm) than in bulk soil (50-75 mm from burrow). This suggests that biochemical drilosphere effects of anecic earthworms, at least in the uppermost portion of the burrow, extend farther than the 2 mm layer assumed traditionally. (C) 2013 Elsevier Ltd. All rights reserved.