Synergistic Effects but Divergent Responses: Physiological and Uptake Strategies of Inula britannica L. under Combined Cd and Pb Stress

Combined contamination by Cd and Pb is widespread in soils, yet plant responses to their co-occurrence remain insufficiently understood. This study investigated how Inula britannica L. responds to single and combined Cd–Pb stress, with emphasis on growth performance, physiological regulation, and metal uptake behavior. Plants were exposed to controlled Cd and Pb treatments, and changes in biomass, chlorophyll content, oxidative stress indicators, antioxidant enzyme activities, thiol-based detoxification compounds, and metal accumulation were systematically assessed. Combined Cd–Pb exposure intensified growth inhibition and oxidative stress compared with single-metal treatments. However, Cd and Pb exhibited contrasting behaviors: Cd showed enhanced uptake and translocation, whereas Pb was predominantly retained in roots with limited mobility. Antioxidant enzymes and thiol compounds were differentially regulated, indicating metal-specific detoxification strategies under combined stress. These results demonstrate that Inula britannica experiences enhanced toxicity under Cd–Pb co-contamination but employs divergent physiological and uptake responses to cope with the two metals. The study provides new insight into plant responses to mixed metal pollution and highlights the potential of Inula britannica for stabilizing Cd–Pb contaminated soils.