Root sequestration and antioxidant defense underpin cadmium tolerance in Arundo donax under contrasting Cd concentrations

Cadmium (Cd) contamination poses a persistent threat to plant growth and environmental safety, yet plant responses to contrasting Cd exposure remain insufficiently understood. Here, Arundo donax seedlings were hydroponically exposed to low (0.1 mM) and high (1.0 mM) Cd stress. Physiological responses were evaluated after 14 d, while transcriptomic profiling at 3 d was used to characterize early molecular responses. Total chlorophyll content decreased by 30.5% and 63.9% under low and high Cd, respectively, and high Cd reduced major gas-exchange parameters by more than 50%. High Cd increased O 2 •− levels by 273.2% and 202.5% in leaves and roots, respectively, and H 2 O 2 by 91.8% and 160.1%, accompanied by enhanced lipid peroxidation and DNA damage. In response, antioxidant and osmotic defenses were activated, with leaf SOD activity increasing by 366.37% under high Cd. Cd was predominantly retained in roots, and the root-to-shoot translocation factor decreased from 0.126 under low Cd to 0.051 under high Cd. Early transcriptomic profiling identified 9798 and 10,964 DEGs in roots under low and high Cd, respectively, compared with 1541 and 4198 in leaves, indicating a stronger early transcriptional response in roots. Changes in Cd transport-related genes were broadly consistent with restricted Cd uptake and translocation and the potential involvement of sequestration-related pathways. Overall, A. donax exhibits dose-dependent physiological and molecular responses involving antioxidant defense, osmotic adjustment, and root-dominant Cd retention, supporting its potential for phytostabilization of Cd-contaminated environments.