Coordinated Growth and Physiological Adaptations to Cadmium Stress in Pomegranate (Punica granatum L.) Seedlings

Phytoremediation utilizing woody plants represents a promising approach for mitigating cadmium (Cd) contamination; however, the potential of ornamental species such as Punica granatum L. (pomegranate) remains insufficiently characterized. This study evaluated the growth performance, physiological responses, and Cd accumulation patterns of pomegranate seedlings exposed to increasing Cd concentrations (T1–T6) in a hydroponic system. High Cd levels (≥T4) markedly suppressed plant growth, as evidenced by reductions in biomass, root necrosis, leaf wilting, and chlorosis. Photosynthetic efficiency was severely compromised, indicated by significant declines in chlorophyll content and key chlorophyll fluorescence parameters (Fv/Fm, ΦPSII, and qP). Simultaneously, increases in the chlorophyll a/b ratio, carotenoid content, and non-photochemical quenching (NPQ) reflected the activation of photoprotective mechanisms. A reduction in stomatal conductance (Gs) and net photosynthetic rate (Pn), coupled with elevated intercellular CO2 concentration (Ci), suggested that non-stomatal limitations were primarily responsible for photosynthetic inhibition. Cd exposure also triggered oxidative stress, as shown by increased levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2). In response, seedlings activated antioxidative and osmotic adjustment pathways, including elevated peroxidase (POD) activity and the accumulation of glutathione (GSH), proline, soluble proteins, and sugars. Notably, pomegranate displayed a root-based Cd sequestration strategy, with high root accumulation (bioconcentration factor, BCF > 271) and minimal translocation to aerial tissues (translocation factor, TF < 0.17). These findings demonstrate that pomegranate seedlings exhibit pronounced tolerance to Cd stress and substantial bioaccumulation capacity, supporting their potential application as ornamental woody species for phytoremediation of Cd-contaminated environments.