Valorization of bamboo vinegar through modified biochar for synergistic cadmium immobilization and phosphorus...

Heavy metal contamination in saline-alkali soils poses a dual challenge of excessive alkalinity and nutrient deficiency, particularly phosphorus (P). Traditional biochar remediation often exhibits limited efficacy in these complex matrices due to the high ionic strength and recalcitrant P fractions. In this study, a bamboo vinegar-modified biochar (MB) was developed to simultaneously remediate cadmium (Cd) and activate P in saline-alkali soil. Modification significantly enhanced biochar textural properties, increasing the specific surface area and pore volume by 330.6% and 298.6%, respectively. MB application substantially ameliorated soil alkalinity and salinity, achieving superior reductions in pH (12.2%), ionic strength (48.8%), and sodium adsorption ratio (41.2%) compared to pristine biochar. MB induced a profound redistribution of Cd speciation, decreasing bioavailable Cd by 42.3% and expanding the residual pool by 29.6%. Simultaneously, the P availability coefficient was enhanced by 166.2%, driven by the dissolution of recalcitrant calcium-bound P and the mineralization of organic P. Mechanistic investigations reveal that MB establishes a synergistic remediation pathway integrating persistent acidification, desalination-driven immobilization, and microbial revitalization. The reduction in Cd toxicity and improved physiochemical environment stimulated the absolute abundance of P-solubilizing bacteria and phosphatase-encoding genes (phoC and phoD). Overall, our study highlights the potential of multifunctional modified biochar to overcome chemical and biological barriers, offering a sustainable strategy for the integrated management of nutrient cycles and heavy metal risks.