Growing maize while biological remediating a multiple metal-contaminated soil: a promising solution with the hyperaccumulator plant Sedum alfredii and the earthworm Amynthas morrisi

Abstract

This study was aimed to investigate the effect of earthworm Amynthas morrisi on the metal bioaccumulation by two plant species, Sedum alfredii Hance (Sedum) and maize (Zea mays L.), in a co-cropping system and possible influencing pathways, and assess the remediation potential of all combination of these organisms to identify the best option. In this study, an eight-week microcosm experiment was conducted to investigate the main and interactive effects of the earthworm Amynthas morrisi, the hyperaccumulator plant Sedum alfredii Hance (Sedum), and maize (Zea mays L.) on C and N forms, and microbial characteristics and diethylene triamine penta acetic acid (DTPA) extractable metals of a soil heavily contaminated by multiple metals (i.e., Cd, Zn, Pb, and Cu). In addition, plant growth and metal accumulation were evaluated and the possible influencing pathways of metal accumulation by the two plant species were assessed. Finally, a remediation strategy was proposed based on the amounts of metals removed by sedum and maize. The soil quality index achieved after eight weeks of experiments, was best with Sedum, and worst in the control with no plants and no earthworms. A path analysis suggests that earthworms exerted strong effects on plant metal accumulation by changing plant growth, with soil microbes playing a mediating role. The association of Sedum and Maize significantly increased the Zn concentration and decreased the Pb and Cu concentrations in the aboveground parts of Sedum compared with Sedum alone, whereas Sedum decreased the Zn, Cd, Pb, and Cu concentrations in the aboveground parts of maize compared with maize alone treatment. PCA showed that when maize was co-cropped with Sedum, metal transfer from its roots to the aboveground parts decreased. The Earthworm + Sedum + Maize treatment displayed the most effective Cd and Zn removal, indicating that the combined introduction of A. morrisi and S. alfredii can effectively remediate soils co-contaminated by Cd and Zn in maize cropping systems.