Ageing effects on nitrogen dynamics and enzyme activities in casts of Aporrectodea caliginosa (Lumbricidae)

Earthworm casts are stable structures characterized by higher nutrients contents, microbial biomass and activity than uningested material, thereby constituting hotspots of microbial-driven processes such as nutrient release or nutrient immobilization and decomposition. Here we studied the changes that ageing produced in the chemical and microbiological properties of casts of the earthworm Aporrectodea caliginosa (Savigny, 1826). The results obtained showed that ageing favoured the release of microbial retained N, mainly as dissolved organic nitrogen, and which was associated with the high protease activity observed. In addition we found an age-dependent decrease in both microbial biomass and activity, which were stimulated by the addition of glucose. This could indicate the existence of C limitation for microbial metabolism in casts, but the enhanced β-glucosidase and cellulase activities suggest that new pools of labile C may be used by microbes during ageing of casts.