Solanum spp. straw improves phytoremediation ability of hyperaccumulator Galinsoga parviflora on cadmium-contaminated soil

Cadmium (Cd) is a major cause of soil contamination in farmlands. To improve the phytoremediation ability of hyperaccumulators, the straws of three Solanum spp. (Solanum alatum, Solanum nigrum var. humile, and Solanum nigrum) were added to Cd-contaminated soil, and Cd-hyperaccumualtor Galinsoga parviflora were planted in the soil to explore their effect on phytoremediation ability of G. parviflora. The straws of three Solanum spp. increased the biomass of G. parviflora, but had no significant effects on the photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid) contents in G. parviflora. The straws of three Solanum spp. decreased or had no significant effects on the superoxide dismutase activity and soluble protein content of G. parviflora, however, they enhanced the catalase activity of this plant. The straw of S. nigrum var. humile enhanced the peroxidase activity of G. parviflora, whereas the straws of S. alatum and S. nigrum decreased the peroxidase activity of G. parviflora. The straws of three Solanum spp. increased the Cd content in shoots and the Cd extraction by shoots of G. parviflora. Compared with the control, the straws of S. alatum, S. nigrum var. humile, and S. nigrum increased the Cd extraction by shoots by 46.41%, 35.33%, and 41.20%, respectively. Correlation and gray relational analyses revealed that the root biomass, shoot biomass, and catalase activity were closely associated with the Cd extration by shoots of G. parviflora. These results indicate that the straws of three Solanum spp. can promote the growth and Cd uptake of G. parviflora, thus improving its phytoremediation ability.