Biochar and metal-immobilizing Serratia liquefaciens CL-1 synergistically reduced metal accumulation in wheat grains in a metal-contaminated soil

Abstract

Biochar and metal-immobilizing bacteria play an important role in reducing the metal uptake of plants. However, little research has characterized the synergistic effects of biochar and metal-immobilizing bacteria on reducing metal accumulation in wheat grains and the underlying mechanisms. In this study, the effects of biochar, metal-immobilizing Serratia liquefaciens CL-1, and biochar + CL-1 on grain Cd and Pb uptake in wheat (Triticum aestivum L. Sumai-188) and the mechanisms involved under field conditions were characterized. Biochar, CL-1, and biochar + CL-1 reduced wheat grain Cd and Pb contents by 17–25%, 24–27%, and 45–55% and reduced the available Cd and Pb contents in the rhizosphere soils by 14–33%, 13–38%, and 27–57%, respectively, compared with the controls. Biochar, CL-1, and biochar + CL-1 increased soil pH values. CL-1 and biochar + CL-1 increased putrescine contents by 93% and 150% and bacterial aguA gene copy numbers by 30% and 44%, respectively, in the rhizosphere soils compared to the controls based on qPCR analysis. Furthermore, biochar + CL-1 reduced the Cd and Pb bioconcentration and translocation factors by 23–33% compared to the controls. CL-1 significantly increased the pH and reduced water-soluble Cd and Pb concentrations (18–44%) in the metal-contaminated soil solution compared to the controls. The results showed a synergistic effect of biochar and CL-1 on the reduction of Cd and Pb accumulation in wheat grains. These findings suggested that biochar plus CL-1 reduced wheat grain metal uptake by reducing metal availability and translocation from the roots to grains and increasing pH levels, putrescine production, and aguA gene abundance, and they highlight the possibility of developing an effective technique for reducing the metal uptake of wheat grains using biochar plus metal-immobilizing bacteria in metal-contaminated soils.