Combined effects of elevated CO 2 and Cd-contaminated soil on the growth, gas exchange, antioxidant defense, and Cd accumulation of poplars and willows

•Elevated CO2 (EC) stimulates leaf photosynthesis, and then increases plant growth.•EC enhances the phytoremediation efficiency, especially under high Cd treatment.•EC decreases oxidative damage by increasing photosynthesis.•EC decreased oxidative damage by increasing antioxidant enzyme activities.•Photosynthesis well maintained under Cd treatment avoids membrane lipid peroxidation.