Fig. 4 The percentage of initially added excess ¹⁵N that was recovered in the 53–2000 µm size fraction of POM in the 0–5 cm soil layer of cores treated with ¹⁵N-labeled KNO₃ (upper panel), rye (middle panel) or manure (lower panel), and incubated with or without worms . Asterisks and error bars are as for Fig. 1