[Regulation Mechanism of Mg/Fe-LDH Modified Biochar on Cadmium Tolerance and Cadmium Reduction in Rice]

Modified biochar has emerged as a pivotal material in environmental remediation due to its superior specific surface area, porous structure, and abundant surface functional groups. To evaluate the feasibility of modified biochar in enhancing cadmium (Cd) tolerance and reducing Cd accumulation in rice, this study synthesized magnesium-iron layered double hydroxide-modified biochar (Mg/Fe-LDH@BC) from rice straw-derived biochar (BC) via a hydrothermal method. The regulatory mechanisms of Mg/Fe-LDH@BC on rice growth, Cd uptake, subcellular distribution, and cell wall component interactions were systematically investigated. The results demonstrated that the application of 50 mg·L^-1 and 100 mg·L^-1 LDH@BC significantly improved rice shoots and roots biomass in rice, plant height, and root length under Cd stress, while alleviating oxidative damage, with superior efficacy compared to pristine BC. Moreover, LDH@BC reduced Cd content in roots and shoots by 34.8%-41.7% and 42.9%-52.8%, respectively, and decreased the Cd translocation factor by 12.5%-19.1%. The analysis of the subcellular distribution of Cd indicated that 100 mg·L^-1 LDH@BC increased the proportion of Cd in the root cell wall and decreased the proportion in the soluble fraction, suggesting its role in immobilizing Cd and inhibiting upward translocation. Subcellular distribution analysis revealed that 100 mg·L^-1 LDH@BC enhanced Cd retention in root cell walls and reduced Cd proportion in soluble fractions, indicating its role in immobilizing Cd and inhibiting upward translocation. Mechanistic studies further showed that LDH@BC elevated pectin content in root cell walls, leading to a 23.6% increase in pectin-bound Cd, while reducing Cd allocation to hemicellulose fractions. Chemical speciation analysis confirmed that LDH@BC promoted the transformation of Cd into less mobile NaCl-exchangeable forms and decreased the highly mobile water-soluble Cd fraction. These findings highlight a dual regulatory mechanism that LDH@BC not only reduces Cd uptake by rice but also enhances Cd sequestration in root cell walls by stimulating pectin biosynthesis, thereby effectively inhibiting Cd translocation from roots to shoots. This study identifies the potential of Mg/Fe-LDH@BC as a high-performance material for Cd-contaminated soil remediation, offering both ecological and agricultural benefits.