Fig. 2 The percentage of initially added excess ¹⁵N that was incorporated into the 5–20 cm soil layer in cores treated with ¹⁵N-labeled KNO₃ (upper panel), rye (middle panel) or manure (lower panel), and incubated with (shaded bars) or without (open bars) earthworms . Asterisks and error bars are as for Fig. 1