Phosphorus-Enriched Biochar Promotes Brassica napus L. Growth under Cadmium Stress by Immobilizing Cadmium and Sustained Phosphorus Release
Cadmium (Cd) contamination in farmland soils poses a threat to food security, necessitating effective remediation strategies. This study prepared three types of phosphorus-enriched biochar (PBC) from rice straw and different phosphorus sources (fused calcium magnesium phosphate, citric acid-activated fused calcium magnesium phosphate, and monocalcium phosphate) to evaluate their potential in stabilizing Cd(II), releasing phosphorus, and enhancing plant resistance to heavy metal stress. Under Cd stress, PBC amendments significantly improved soil physicochemical properties and reduced Cd bioavailability through direct immobilization (adsorption, precipitation) and indirect mechanisms. Specifically, CBC and MBC treatments reduced DTPA-extractable Cd by 45.73% and 48.92%, respectively. The porous structure of biochar facilitated sustained phosphorus release, influencing soil solution phosphorus dynamics. In pot experiments with Brassica napus L., PBC application significantly improved agronomic traits and reduced oxidative stress markers. The C5 treatment increased leaf area by 100%, M7 increased plant height by 26.8%, and M3 reduced malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents by 72.5% and 61.2%, respectively. These findings demonstrate that PBC effectively alleviates Cd toxicity, promotes plant growth, and enhances stress resistance, offering a feasible strategy for remediating Cd-contaminated soils while providing a sustainable phosphorus source.