Rhizospheric regulation and antioxidative defense mediate species-specific phytoremediation efficiency in multi-metal...

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 O₂ 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.