Rhizospheric Regulation and Antioxidative Defense Mediate Species-Specific Phytoremediation Efficiency in Multi-Metal Contaminated Soils

Effective phytoremediation of multi-metal contaminated soils requires understanding species-specific strategies that integrate rhizospheric engineering with physiological defense mechanisms. This study compared the phytoremediation responses of Medicago sativa , Bidens pilosa , and Celosia argentea under cadmium (Cd), lead (Pb), and zinc (Zn) co-contamination. B. pilosa and C. argentea exhibited higher shoot metal accumulation and translocation factors (TF > 1.5), attributed to efficient root-to-shoot transport and favorable rhizospheric conditions, including moderate pH and elevated β-glucosidase, acid phosphatase, and alkaline phosphatase activities. In contrast, M. sativa showed limited shoot accumulation due to sustained O 2 release and rhizospheric alkalization, which reduced metal solubility and availability. At the physiological level, all species experienced metal-induced oxidative stress, evidenced by elevated root malondialdehyde (MDA) concentrations. However, shoot responses diverged markedly: B . pilosa maintained oxidative homeostasis with stable shoot MDA levels, while C . argentea and M . sativa showed progressive oxidative burden. Metallothionein-based detoxification strategies also varied tissue and species specifically. Root tissues generally upregulated glutathione (GSH) and phytochelatin (PC) biosynthesis, yet foliar responses differed: GSH predominated in B . pilosa leaves, whereas PCs dominated in C . argentea and M . sativa . Antioxidant enzyme profiles further distinguished species strategies: B . pilosa and C . argentea showed coordinated catalase (CAT) and peroxidase (POD) upregulation in shoots, while M . sativa exhibited enzymatic imbalances indicative of compromised oxidative defense. These findings establish a mechanistic framework linking rhizosphere modification, metal translocation efficiency, and antioxidative capacity, providing critical insights for rational plant selection in tailored phytoremediation programs targeting multi-metal contaminated environments. • Cd-remediation species differentially co-accumulate Cd, Pb, and Zn. • B. pilosa and C. argentea show higher TFs and metal sequestration capacity. • GSH–phytochelatin pathways mitigate ROS-induced oxidative damage. • Rhizospheric β-glucosidase and phosphatases enhance DGT-labile Cd, Pb, and Zn.