Interactive effects of bacteria-loaded biochar on the physiological responses of Brassica rapa var. chinensis in the Pb and Zn contaminated soil

Abstract

Lead (Pb) and zinc (Zn) are widely recognized as common environmental contaminants, contributing to soil degradation and posing risks to environmental health. Combining functional carbon-based materials with microorganisms has been considered as an effective and environmentally friendly strategy for remediating Pb/Zn-contaminated soil. However, there is still a lack of understanding the connection between heavy metal immobilization and plant responses, which hampers practical applications. Here, a 90-day pot experiment was conducted to investigate the integrated effects of biochar (WS700) and microorganisms including inorganic phosphate-solubilizing bacteria (IPSB) and sulfate reducing bacteria (SRB) on Pb and Zn synchronous immobilization and the physiological responses of Brassica rapa var. chinensis (Brassica). Compared with CK, bacteria-loaded biochar treatment declined the exchangeable Pb and Zn fraction by 94.69%–98.37% and 94.55%–99.52%, while increasing the residual state Pb and Zn by 75.50%–208.58% and 96.71%–110.85%, respectively. Three amendments enhanced Brassica growth by improving total chlorophyll content and superoxide dismutase (SOD) and peroxidase (POD) activities. The bacteria-loaded biochar treatment effectively regulated stomatal conductance and reduced intercellular CO₂ concentration. Moreover, compared with CK, three amendments reduced MDA content by 28.84%, 28.30% and 41.60%, respectively, under the high concentration of Pb and Zn. The findings demonstrated the significant role of bacterial-biochar consortia in immobilizing Pb and Zn and mitigating Pb and Zn-induced stress in plants by regulating photosynthetic characteristics and antioxidant enzyme activities.

Keywords

biochar / immobilized bacteria consortia / photosynthetic properties / Pb and Zn immobilization / antioxidant enzymes

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