| Summary: | Heavy metal pollution is one of the major agronomic challenges. Tungsten (W) exposure leads to its accumulation in plants, which in turn reduces plant growth, inhibits photosynthesis and induces oxidative damage. In addition, the predicted increase in CO<sub>2</sub> could boost plant growth under both optimal and heavy metal stress conditions. The aim of the present study was to investigate the effect of W on growth, photosynthetic parameters, oxidative stress and redox status in rye plants under ambient and elevated (eCO<sub>2</sub>) levels. To this end, rye plants were grown under the following conditions: ambient CO<sub>2</sub> (aCO<sub>2</sub>, 420 ppm), elevated CO<sub>2</sub> (eCO<sub>2</sub>, 720 ppm), W stress (350 mg kg<sup>−1</sup> soil) and W+eCO<sub>2</sub>. W stress induced significant (<i>p</i> < 0.05) decreases in growth and photosynthesis, increases in oxidative damages (lipid peroxidation) and the antioxidant defense system, i.e., ascorbate (ASC), reduced glutathione (GSH), GSH reductase (GR), peroxidase (POX), catalase (CAT), superoxide dismutase (SOD), ASC peroxide (APX) and dehydroascorbate reductase (DHAR). On the other hand, eCO<sub>2</sub> decreased W uptake and improved photosynthesis, which sequentially improved plant growth. The obtained results showed that eCO<sub>2</sub> can decrease the phytotoxicity risks of W in rye plants. This positive impact of eCO<sub>2</sub> on reducing the negative effects of soil W was related to their ability to enhance plant photosynthesis, which in turn provided energy and a carbon source for scavenging the reactive oxygen species (ROS) accumulation caused by soil W stress.
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