Effects of biochar and the geophagous earthworm Metaphire guillelmi on fate of 14C-catechol in an agricultural soil

Both biochar and earthworms can exert influence on behaviors of soil-borne monomeric phenols in soil; however, little was known about the combined effects of biochar and earthworm activities on fate of these chemicals in soil. Using 14C-catechol as a representative, the mineralization, transformation and residue distribution of phenolic humus monomer in soil amended with different amounts of biochar (0%, 0.05%, 0.5%, and 5%) without/with the geophagous earthworm Metaphire guillelmi were investigated. The results showed biochar at amendment rate <0.5% did not affect 14C-catechol mineralization, whereas 5% biochar amendment significantly inhibited the mineralization. Earthworms did not affect the mineralization of 14C-catechol in soil amended with <0.5% biochar, but significantly enhanced the mineralization in 5% biochar amended soil when they were present in soil for 9 d. When earthworms were removed from the soil, the mineralization of 14C-catechol was significantly lower than that of in earthworm-free soil indicating that 14C-catecholic residues were stabilized during their passage through earthworm gut. The assimilation of 14C by earthworms was low (1.2%), and was significantly enhanced by biochar amendment, which was attributed to the release of biochar-associated 14C-catecholic residues during gut passage of earthworm.