Fig. 1 The percentage of initially added excess ¹⁵N that was incorporated into the 0–5 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 indicate significant differences (P < 0.05) between cores with or without worms. Error bars are standard errors