Figure 2: Net loss of SOC compared with the initial field soil.

Phase I: Sieved field soil (white block) was incubated with (coloured blocks) and without (control; grey block) earthworms for 23 days. Earthworms: L. rubellus (Lu; orange block), A. agrestis (Am; light blue block). Phase II: The incubated control soil and the two newly obtained earthworm-worked soils were incubated for an additional 31 days after removing earthworms. Values inside the boxes are the mean of SOC content (g C kg⁻¹ dw soil), with±1 s.e.m. indicated by error bars. A one-sample t-test (two-tailed) was performed between the mean organic C content of the initial field soil (n=9) and the SOC content of the field soil with and without earthworm incubation (n=3) after 23 days and again after further 31 days incubation; bars marked with ‘*’ indicate significant decline of soil C content compared with the mean C content of the initial field soil with date for a given treatment. A one-way ANOVA was performed to examine the differences among the control soil and the two earthworm-worked soils (that is, Asoil and Lsoil; n=3) at the end of phase II; bars marked with the letter ‘a’ indicate non-significant (P>0.05) differences of soil C content among treatments at day 54.