Background Cadmium (Cd) is considered to be a highly toxic and non-biodegradable pollutant, which is easily absorbed by plant roots and transferred to other parts, and stored in leafy vegetables. Seed germination and seedling root development are important stages of plant growth cycle, while Cd significantly inhibits the seed germination and seedling growth of pakchoi cabbage. Green waste compost (GWC) was used as remediation material to alleviate the inhibition of Cd on the seed germination and seedling growth of pakchoi cabbage, so as to provide theoretical basis for preventing early damage of pakchoi cabbage by Cd and controlling Cd contaminated soil.

Methods Pakchoi cabbage seeds were treated with different Cd²⁺ concentration solutions and GWC adsorption solutions (0, 5, 10, 25, 50, 100 and 200 mg/L). The characterization of GWC before and after adsorption of Cd²⁺ by GWC and its effect on the adsorption efficiency and adsorption capacity of Cd²⁺ were determined. The seed germination potential, germination rate, germination index and vigor index, root and shoot growth and root and shoot inhibition rate, Cd accumulation and transfer coefficient of pakchoi cabbage were determined.

Results The SEM-EDS image analysis showed that Cd²⁺ was adsorbed on GWC. GWC had obvious adsorption effect on Cd²⁺ with different solubility, and the adsorption efficiency was 97.66%-98.91%. Cd stress reduced the germination potential, germination rate, germination index and vigor index of pakchoi cabbage seeds, and inhibited the growth of pakchoi cabbage seedlings. GWC treatment significantly alleviated the inhibition of Cd²⁺ stress on seed germination, and improved the germination index of pakchoi cabbage seeds under Cd²⁺ stress. The results showed that Cd had a "low promotion and high inhibition" effect on shoot growth. Compared with the control, the shoot length of pakchoi cabbage increased by 28% and 29% under 5 and 10 mg/L Cd²⁺ concentration treatments, but the root and shoot length inhibition rate increased significantly with the increase of Cd²⁺ concentration (P < 0.05). After GWC treatment, the root length of pakchoi cabbage first increased and then decreased, and the root length inhibition rate was -6%-44%; it significantly promoted the shoot length growth of pakchoi cabbage (P < 0.05), and the inhibition rate of shoot length was negative. The increase of Cd concentration in roots and shoots of pakchoi cabbage increased, but the translocation factor decreased. After GWC treatment, Cd content in roots and shoots of pakchoi cabbage decreased significantly, and the translocation factor ranged from 0.82 to 1.00.

Conclusions In the important growth stages of seed germination and seedling root development, the GWC may substantially alleviate the inhibition of Cd²⁺ stress on the seed germination and seedling growth of pakchoi cabbage, reduce the accumulation of Cd, and prevent the early damage of Cd to pakchoi cabbage. It can available for reference to crop production activities and related basic research in heavy metal polluted farmland.