ObjectiveThis paper aims to study the effects of single and combined stress of lead and cadmium at different concentrations on seed germination and seedling growth of mulberry, as well as the bio-enrichment and transfer of Pb and Cd in mulberry to explore the repair capacity of mulberry on contaminated soil.

MethodThe germination and pot-based experiment was designed with different concentrations Pb (0, 250, 500, 750, 1 000, 1 250 mg/kg) and Cd (0, 0.2, 1, 25, 75, 100 mg/kg) to study the germination rate of seed, plant height and biomass of mulberry, as well as the enrichment and transfer coefficients of Pb and Cd in mulberry roots, stems and leaves.

Result(1) The germination of mulberry seeds was inhibited by single and combined stress at different concentrations of Pb and Cd. (2) Low concentrations of Pb and Cd (250, 0.2 mg/kg) promoted the high biomass of mulberry seedlings, which turned into inhibition when the concentration increased. (3) Pb and Cd were mainly accumulated in mulberry roots, and low concentration of Pb (250 mg/kg) would promote Cd enrichment and transfer in mulberry. The enrichment coefficient and transfer coefficient of Cd were higher than Pb, but the maximum values of both were less than 1. The bio-enrichment coefficient and transfer coefficient of combined stress were lower than those of single stress. The enrichment coefficient and transfer coefficient of Pb and Cd will be reduced when the concentration of Pb and Cd increased.

ConclusionThe germination of mulberry seeds is inhibited by different concentrations of Pb and Cd, and the inhibitory effect increases with the increase of Pb and Cd concentration. Although mulberry is not a hyper-accumulator, the enrichment coefficient and transfer coefficient of low-concentration Pb and Cd are relatively high, and low-concentration Pb and Cd would promote the growth of mulberry, which can be used to plant mulberry and raise silkworm in soil contaminated with low-concentration Pb and Cd for soil heavy metal pollution remediation.