Application of X-ray tomography to evaluate liming impact on earthworm burrowing activity in an acidic forest soil under laboratory conditions

Abstract

This study investigated the burrowing activity responses of two earthworm species (Aporrectodea caliginosa and Aporrectodea giardi) with contrasting ecological strategies to lime application under laboratory conditions. The impact of liming on earthworm burrowing activity was measured in 25-cm, repacked soil cores sampled from an acidic forest of the Vosges Mountains (North-eastern, France). Soil treatments included: (i) a non-limed field soil (OH horizon, 0–5cm, pH=3.8; A horizon, 5–25cm, pH=4.5) that had received decades of atmospheric acidic deposition, (ii) an in situ limed soil (OH, 0–5cm, pH=4.1; A horizon, 5–25cm, pH=4.7) that had been limed at 2.5tha−1 six years prior to sampling for this experiment and (iii) an in vitro non-limed field OH horizon limed in the laboratory to 2.5tha−1 equivalence over a non-limed A horizon (OH, 0–5cm of core, pH=5.4; A horizon, 5–25cm, pH=4.5). After 9weeks of incubation, X-ray computed tomography was used to characterize the burrow system of the two earthworm species for each of the three soil treatments. Soil pH, amount of surface casts, and earthworm biomass were also measured. All earthworms were alive at the end of the experiment. A. giardi lost significantly less weight and produced more surface casts than A. caliginosa. The in vitro liming increased total burrow volume and length of A. giardi. Liming had no effect on A. caliginosa biomass, surface cast production or total burrow system volume and length. However, in vitro liming significantly enhanced A. caliginosa burrowing activity in the OH horizon. Finally, for both species, the burrowing activity was not improved into the in situ limed treatment.