Earthworm activity effectively mitigated the negative impact of microplastics on maize growth

Microplastic pollution can have detrimental effects on soil environments and inhibit crop growth. Earthworms, known as soil engineers, promote crop growth, but their role and impact on the amelioration of microplastic-polluted soil is not yet clear. In this study, we investigated the impact and pathways of earthworm activity on microplastic-contaminated soil by introducing varying densities (without earthworm:0, low-density: 1, medium-density: 2, high-density: 5 ind column-1) of earthworms (epi-endogeic) into soil contaminated with two types of microplastics: polyethylene and polyvinyl chloride. Our results showed that earthworms all survived in soil polluted with two types of microplastics. Meanwhile, earthworm activity increased nutrient content and enzyme activity by 0.2-36.1% and 2.9-34.3%, respectively, and significantly increased soil microbial biomass and community diversity index. Earthworm activity also decreased antioxidant enzyme activity and promoted maize plant growth, including agronomic traits such as plant height, biomass, root length, and root surface area. Furthermore, the nutrient content of maize organs increased by 1.1-29.7%. Partial least squares models confirmed that earthworm activity alleviated the stress effect of microplastic pollution on plant growth by improving soil structure, fertility, and microbial abundance and diversity. The greatest effect on maize growth was observed with the improvement of soil physical-chemical properties. Our results suggest that medium densities of earthworms have the greatest soil improvement effect and provide an important basis for bioremediation of farmland contaminated by microplastics and promoting green and efficient development in agriculture.