A simple and rapid method for labelling earthworms with 15N and 13C

A simple, rapid and cost-effective laboratory method was developed for labelling soil-feeding earthworms simultaneously with 15N and 13C. The method circumvents the production of labelled plant material and can be adapted to devise pulse-labelling or long-term labelling protocols. Soil was amended with 15NH4+ and incubated for 7 days. Then, U-13C-glucose was added and endogeic earthworms, Aporrectodea caliginosa (Oligochaeta: Lumbricidae), were provided individually with 4 g of this pre-incubated soil. The labelling period was 4 days. The labelling efficiency (percentage of tracer retained in earthworm tissues) was estimated to be 15.8% for 15N and 10.3% for 13C. The loss of 15N and 13C label from tissue and mucus was traced for 21 days post-labelling. Label loss from mucus was best described by a two-term exponential function, whereas the label loss in body tissue followed a single-term exponential function. Half-life estimates for the 15N and 13C tracers in body tissue were 16 and 37 days, respectively.