Long-term regulation of maize crop residue carbon accumulation in soil and aggregates by epigeic and endogeic earthworms is tillage regime-specific

Earthworms influence soil carbon (C) sequestration by modulating the balance between plant residue C incorporation and soil C mineralization below ground. The knowledge of the prolonged effects and backstaging mechanisms of C sequestration by earthworms belonging to different ecological groups in no-tillage (NT) and conventional tillage (CT) agroecosystems is still surprisingly sketchy. Therefore, we analyzed the contribution of the epigeic species Eisenia nordenskioldi (Eisen) and the endogeic species Metaphire tschiliensis (Michaelsen) to the distribution of C in soil and soil aggregates of different sizes from the 13C-labeled maize residue. For this, we ran a 337-day-long mesocosm experiment with simulated NT and CT systems. At the end of the experiment, epigeic and endogeic earthworm treatments in NT soil significantly increased SOC concentration by 16.61% and 17.31%, respectively if compared with the situation on day 40. However, no significant effects were observed in CT soil. In NT soil, the presence of M. tschiliensis significantly increased residue-derived C in SOC, whereas this effect was not significant in CT soil. The presence of M. tschiliensis increased the 13C content in all soil aggregate size classes in both NT and CT soils at the end of the experiment. The interaction between the two earthworm species treatments significantly positively affected the 13C content across all soil aggregate size classes in NT soil. This means that in NT soil, earthworms can aid the accumulation of larger amounts of 13C via enriching soil aggregates with C derived from crop residues. Our study further demonstrated that compared to epigeic earthworms, endogeics are more likely to promote the retention of maize residue-derived C in soil. Such differential contribution of the two ecological groups of earthworms explored to the stabilization of C in aggregates highlights the need for functionally diverse soil macrofauna in agroecosystems to achieve synergies in the delivery of essential ecological services in low input agriculture.