Rhizosphere‐driven alteration of cadmium bioavailability under Cd stress

Abstract Rhizosphere processes are recognized as critical factors influencing the efficiency of phytoremediation, particularly for heavy metal‐contaminated soils. This study investigates how rhizosphere effects alter the distribution of cadmium (Cd) among soil fractions with distinct plant availability under varying Cd stress conditions, using Bidens pilosa as a model species. A gradient of Cd concentrations (0–80 mg/kg) was applied to soil, and Cd fractionation, soil enzymatic activities, and pH were analyzed in rhizosphere and non‐rhizosphere zones. Results revealed that the rhizosphere significantly shifted Cd partitioning: the proportion of Cd in potentially more bioavailable fractions (reducible and oxidizable) increased, while the less plant‐available fractions (residual) decreased. Concurrently, rhizosphere pH was consistently lower, and urease/catalase activities correlated with Cd redistribution. These findings suggest that rhizosphere‐induced acidification and enzymatic changes drive Cd mobilization from recalcitrant to more plant‐accessible phases. Combined with elevated Cd accumulation in plants, our study demonstrates that rhizosphere processes enhance Cd bioavailability by modifying its binding forms, providing a mechanistic basis for optimizing phytoremediation strategies in Cd‐contaminated environments.