Effect of Biochar and Earthworms on Mineralization of Organic Matter in Top Soil and Deep Soil

Biochar has been widely used for soil remediation and carbon sequestration. However, the effects of biochar and earthworms on the mineralization of soil organic matter (SOM) remain controversial. In this study, SOM mineralization in top and deep soils with or without earthworm activity and 0.5% (w/w) maize straw biochar was investigated during a 43-day incubation experiment. The results showed that the organic carbon content was reduced after incubation, particularly during earthworm activity. The addition of biochar retained easily degradable fractions (such as tryptophan and tyrosine), whereas earthworms promoted the degradation of these fractions. Earthworms significantly increased the soil respiration rate and soil carbon emissions. The addition of biochar stimulated SOM mineralization under the effect of earthworms in the top soil within 7 days; however, biochar inhibited carbon emissions under earthworm activity for a longer time. Compared with deep soil, earthworms had a stronger respiration effect on top soil, which was mainly attributed to the more easily degradable SOM in the top soil. Overall, the positive effects of biochar on carbon sequestration were more pronounced under earthworm activity. This study emphasizes that soil mineralization was affected by biochar and soil macrofauna, particularly in areas with intense human activity.