Effects of Applying Lychee Biochar on the Absorption, Accumulation of Lead, Cadmium and Arsenic in Sunflower Plants in Heavy Metal Contaminated Soil

Different amounts of lychee biochar (2.5%, 5% and 10%) were added to heavy metal contaminated soils, with the purposes to analyze and compare the effects of biochar addition on the biomass of sunflower plants and accumulation and distribution of Pb, Cd and As in the sunflower plant and organ. The primary results of the experiments are as follows:With increasing amount of biochar, the biomass of sunflower plants increased significantly. At the addition of 5%, the biomass of sunflower plants reached the maximum, but excessive biochar inhibited the growth of sunflower. The addition of biochar enhanced the ability of sunflower to repair heavy metal contaminated soil. The total amount of Pb, Cd and As accumulated in sunflower plants increased significantly compared to the control group. The increase ranges were 22.90%-58.92%, 15.76%-42.25% and 67.92%-109.78% for Pb, Cd, As, respectively. The addition of biochar in heavy metal contaminated soil significantly increased the contents of Pb, Cd and As in leaves and receptacles of sunflower, but the contents in roots, stems and seeds decreased significantly with the increase of biochar. The contents of Pb, Cd and As in sunflower seeds decreased by 78.13%, 46.18% and 50.23%, respectively, compared to the control group. Although application of biochar to the contaminated soils could reduce effectively heavy metal contents in sunflower seeds, Pb and Cd contents in sunflower seeds were still higher than the contamination limit in the National Food Safety Standards (GB 2762-2017) in nuts and seeds (0.2 and 0.5 mg·kg^-1, respectively). It is not edible and can be used as a bio-energy material.