Combined stress of Pb and Cd toxic effects on physiological response and potentially toxic elements accumulation characteristics in Cunninghamia lanceolata seedlings.

The extensive contamination of terrestrial ecosystems with multiple potentially toxic elements (PTEs) necessitates elucidation of plant adaptive mechanisms under combined PTEs stress. This study examines the physiological adaptations, antioxidant regulation, and PTEs allocation patterns in Cunninghamia lanceolata seedlings exposed to lead (Pb) stress (Pb4, 4.0 mg kg-1 Pb; Pb40, 40 mg kg-1 Pb), cadmium (Cd) stress (Cd2, 2 mg kg-1 Cd; Cd20, 20 mg kg-1 Cd), and combined Pb and Cd stress. Results demonstrated concentration-dependent inhibition of biomass production and chlorophyll b biosynthesis under both single and combined PTEs stress conditions. Different responses in superoxide dismutase activity were observed under combined stress compared to the controls, with lower concentration Pb stress causing notably higher enzymatic activation compared to higher concentration Pb stress. Elevated Cd concentrations resulted in significant accumulation of malondialdehyde in leaf tissues, indicating membrane damage. Lead preferentially accumulated in leaves under single Pb stress, while Cd predominantly accumulated in root systems. However, when the plants were exposed to combined Pb and Cd stress, the PTEs translocation pathways in the plants were altered, which resulted in a greater retention of Cd in the stems compared to when the plants were exposed to the single PTE stress. These findings provide insights into species-specific PTE homeostasis mechanisms under polymetallic stress, thereby providing theoretical foundations for the development of phytoremediation strategies in environments contaminated with multiple PTEs.