Effects of anecic Amynthas aspergillum on the proportion and depth of straw-derived carbon input into soil

Straw mulching significantly affects the soil organic carbon (OC) pool, but its positive effect on soil OC is limited by the slow decomposition rate and shallow depth. Increasing the conversion rate of straw-derived carbon (C) to soil OC and the depth affected are important for enhancing soil carbon storage and mitigating global climate change. Anecic earthworms feed on surface organic residues and dwell underground; and thus, they can carry surface straw directly underground. However, previous studies have focused on European earthworms, and it is still unclear how Chinese widely distributed earthworms, such as the anecic Amynthas aspergillum, affect the conversion rate of straw-derived C into soil OC and the depth affected, and whether these effects are related to soil properties. Using ¹³C tracing technology, we established treatments with and without A. aspergillum in soil with added straw to examine how A. aspergillum regulate the distribution of straw-derived OC in soil profiles during incubation for 31 days. Soil samples from the plow layer (PL) and plow pan layer (PP) of subtropical corn land were used in this study to represent two soils of different properties. Visible earthworm casts were not observed on the surface soil. A. aspergillum significantly increased the loss of surface straw by 86.1 % and 43.1 % in the PL and PP soils, respectively (p < 0.05). The conversion rate of straw-derived C into soil OC was 21.8 ± 0.5 % in the presence of earthworms in the PL soils, which was significantly greater than that without earthworms (7.9 ± 0.5 %, p < 0.05). The conversion rates were 8.0 % and 12.8 % in the absence and presence of earthworms, respectively, in the PP soils. The A. aspergillum increased the soil depth affected by straw-derived C input in the profiles of both the PL (to 10–20 cm) and PP soils (to 5–10 cm) compared with the treatments without earthworms (0–5 cm). Thus, anecic A. aspergillum promoted the decomposition of straw, enhanced the conversion of straw-derived C into soil OC and depth affected, and the effects of A. aspergillum were greater in the fertile soils. The underground casting behavior of A. aspergillum, may enhance the effects of incorporation of surface straw-derived C in deep soils. We suggest that earthworm regulation combined with straw return could be considered in sustainable agriculture.