Earthworms promote the accumulation of maize root-derived carbon in a black soil of Northeast China, especially in soil from long-term no-till

Recent studies have shown that earthworms regulate dynamics of plant litter and soil organic carbon. However, the effects of earthworms on rhizospheric carbon, which is the main energy source of soil food webs and a vital factor in soil carbon sequestration, remain unclear. Here, a (CO2)-C-13-labeling experiment was performed to determine the effects of earthworms on the fate of maize rhizodeposit carbon from black soil (Mollisol) following conventional tillage (CT) and 14 years (2002-2016) of conservation tillage (no-till, NT). A total of 4 treatments was established: NTE (no-till soil with earthworms), CTE (conventional till soil with earthworms), NTC (control, no-till soil without earthworms) and CTC (control, conventional till soil without earthworms). The results indicated that earthworms increased the amounts of root-derived in soils relative to the amounts in the corresponding no-earthworm control treatments. Maize biomass was significantly higher in the NTE treatment than in the CTE treatment (P < 0.05). Compared with the control treatments (NTC and CTC), the presence of earthworms stimulated maize biomass growth. On day 30 after labeling, the amount of rhizodeposit carbon in NT soil was significantly higher than that in CT soil (P < 0.05), and a higher delta C-13 signature in the soil organic carbon (SOC) was observed in the NTE treatment than in the CTE treatment (P < 0.05). These findings indicate that earthworms in NT soils were more likely due to the higher biomass inputs and were more likely to assimilate rhizodeposit carbon from roots than that in CT soils. We found that neither earthworm presence nor tillage significantly affected the delta C-13 signatures in the labile SOC fractions (dissolved organic carbon, DOC; microbial biomass carbon, MBC and particulate organic carbon, POC). Our results suggest that the presence of earthworm affects microbes and may increase the retention of rhizodeposit carbon. In the earthworm-worked soils, higher amounts of carbon were mineralized by soil microorganisms in the CT soil than in the NT soil. This finding demonstrates that earthworms in NT soils could promote the accumulation of rhizodeposit carbon. Our work highlights how earthworms in long-term NT soil facilitate photosynthesized carbon accumulation belowground.