Biochar was widely developed for the soil amendment and remediation of heavy metal contaminated soil. The Cd hyperaccumulator, Solanum nigrum L., has been paid much more attention with the wide application of phytoremediation. The effects of biochar on the growth and accumulation capacity of Solanum nigrum L. in Cd contaminated soil have not been explored so far. The objectives of this study were to explore the dual effects of biochar addition on available Cd in the soil and hyperaccumulation of Cd in Solanum nigrum L. under different Cd contaminated levels. The correlations of soil physicochemical and biochemical properties and Cd absorption of Solanum nigrum L. were analyzed after a 60-day pot experiment under three biochar doses (0%, 1% and 5%) and four Cd concentrations (0, 25, 50 and 100 mg kg-1). The availability of Cd obtained by DTPA extraction significantly decreased after biochar application (P = 0.003, P = 0.0001, P = 0.0001 under 1% biochar addition for 25, 50, and 100 mg kg-1 Cd concentrations, P = 0.0001, P = 0.0001, P = 0.0001 under 5% biochar addition for 25, 50, and 100 mg kg-1 Cd concentrations, n ≥ 3). The 1% biochar dose significantly increased leaf dry weight (P = 0.039, P = 0.002 for the Cd concentrations of 50 and 100 mg kg-1, n ≥ 3) compared with the control in higher Cd concentrations (50 and 100 100 mg kg-1). In the presence of biochar, the bioconcentration factor (BCF) increased under the Cd concentrations of 50 and 100 mg kg-1. The translocation factors (TF) decreased with the biochar doses under the Cd concentration of 100 mg kg-1. The dose of 5% biochar significantly increased the urease activity by 41.18% compared to the 1% biochar addition in the Cd contaminated soil of 50 mg kg-1 concentration. The activities of acid phosphatase were inhibited by 1% biochar dose in all the Cd contaminated soils. The dry weight of the root of Solanum nigrum L. was significantly negatively correlated with acid phosphatase activity and BCF, respectively, indicating acid phosphatase in the rhizosphere soil of Solanum nigrum L. were repressed by Cd toxicity despite of biochar amendment. Biochar had no negative effect on Cd accumulation ability of Solanum nigrum L. Two-way ANOVA analysis showed that both biochar and Cd significantly affected the height of Solanum nigrum L. and the dry weight of leaf and stem. This study implied that biochar addition does not limit the absorption of hyperaccumulator Solanum nigrum L. in the remediation of Cd-contaminated soil. This study implied that the simultaneous application of biochar and hyperccumulator Solanum nigrum L. is promising during the remediation of Cd-contaminated soil.
Keywords: Available Cd; Biochar amendment; Plant growth; Solanum nigrum.