Earthworms facilitate carbon sequestration through unequal amplification of carbon stabilization compared with mineralization

A recent review concluded that earthworm presence increases CO 2 emissions by 33% but does not affect soil organic carbon stocks. However, the findings are controversial and raise new questions. Here we hypothesize that neither an increase in CO 2 emission nor in stabilized carbon would entirely reflect the earthworms’ contribution to net carbon sequestration. We show how two widespread earthworm invaders affect net carbon sequestration through impacts on the balance of carbon mineralization and carbon stabilization. Earthworms accelerate carbon activation and induce unequal amplification of carbon stabilization compared with carbon mineralization, which generates an earthworm-mediated ‘carbon trap’. We introduce the new concept of sequestration quotient to quantify the unequal processes. The patterns of CO 2 emission and net carbon sequestration are predictable by comparing sequestration quotient values between treatments with and without earthworms. This study clarifies an ecological mechanism by which earthworms may regulate the terrestrial carbon sink. The presence of earthworms in soil may significantly increase CO 2 emissions, but the impacts of earthworms on net carbon sequestration are poorly understood. Zhang et al . introduce a new concept by which the effects of earthworms on the balance of carbon mineralization and stabilization can be quantified.