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 N-15 and C-13. 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 (NH4+)-N-15 and incubated for 7 days. Then, U-C-13-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 N-15 and 10.3% for C-13. The loss of N-15 and C-13 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 N-15 and C-13 tracers in body tissue were 16 and 37 days, respectively. (c) 2004 Elsevier Ltd. All rights reserved.