Table 1.

Enrichment levels (atom % excess, APE, means ± SD) with stable isotopes (¹³C and ¹⁵N) in earthworm tissue and casts (Lumbricus terrestris, Aporrectodea caliginosa) after feeding four days on labelled soil. Results of Kruskal–Wallis–tests comparing five different labelling treatments (for details see Materials and methods section) are provided.

	Treatments					Kruskall–Wallis (df = 4)
	Once + incub	Once + incub + oat	Staggered + incub	Once + no incub	Staggered + no incub	χ2	P
Tissue – 13C APE
L. terrestris	0.146 ± 0.063	0.021 ± 0.009	0.029 ± 0.016	0.012 ± 0.004	0.026 ± 0.015	36.13	<0.001
A. caliginosa	0.062 ± 0.075	0.019 ± 0.012	0.066 ± 0.036	0.054 ± 0.044	0.058 ± 0.042	15.32	0.004
Tissue – 15N APE
L. terrestris	0.556 ± 0.138	0.049 ± 0.024	0.160 ± 0.079	0.082 ± 0.066	0.146 ± 0.056	41.26	<0.001
A. caliginosa	0.352 ± 0.113	0.050 ± 0.035	0.309 ± 0.138	0.363 ± 0.185	0.475 ± 0.176	29.33	<0.001
Casts (days 7–21) – 13C APE
L. terrestris	0.012 ± 0.008	0.007 ± 0.003	0.002 ± 0.001	0.002 ± 0.001	0.005 ± 0.005	15.89	0.003
A. caliginosa	0.008 ± 0.005	0.003 ± 0.003	0.007 ± 0.003	0.004 ± 0.002	0.007 ± 0.004	9.03	0.060
Casts (days 7–21) – 15N APE
L. terrestris	0.706 ± 0.069	0.080 ± 0.038	0.578 ± 0.074	0.464 ± 0.154	0.513 ± 0.144	21.96	<0.001
A. caliginosa	0.664 ± 0.168	0.110 ± 0.029	0.373 ± 0.024	0.113 ± 0.038	0.426 ± 0.094	20.62	<0.001