Abstract <p>Elevated CO₂ (eCO₂) would modify the environmental effects and behaviors of heavy metals. Chromium (Cr) is a toxic heavy metal that exists in several chemical forms. How eCO₂ affects the environmental fate of Cr in plant-soil systems is not clear. Here, we used open-top chambers to investigate the effects of eCO₂ on phytotoxicity, transport and microbial toxicity of Cr (0, 200 and 400 mg/kg) in pakchoi-soil systems. The Cr at 200 mg/kg induced visible beneficial effects on pakchoi growth and increased the fresh weight by 95.0%. The Cr at 400 mg/kg significantly increased malonaldehyde contents under ambient CO₂ levels, but it did not affect antioxidant enzyme activities and increased the chlorophyll b contents by 71.4% under eCO₂ conditions. The highest Cr accumulation was observed at Cr of 200 mg/kg, and eCO₂ significantly increased plant Cr uptake by 19.8%. The Cr exposure reduced soil nitrate content and inhibited the activities of soil catalase, phosphatase and urease. Correlation analysis revealed that soil ammonium and nitrate contents were the main factors influencing Cr fractions, further affecting enzyme activities, indicating that Cr contamination could modify soil quality by changing nitrogen cycling and Cr availability. Overall, this study suggested that Cr contamination modified soil nutrient turnover, and eCO₂ mitigated the Cr phytotoxicity and enhanced Cr uptake, with unknown implications for human health.</p> Graphical Abstract <p></p>