Tomato meets the dietary nutrient and antioxidant requirements of diverse populations. Being a C 3 crop and an important vegetable, it is likely to be influenced by increased CO 2 concentrations under climate change situation. This study was conducted to investigate the effects of elevated CO 2 on overall physiology, water relations, growth, yield, and fruit quality of tomato (Lycopersicon esculentum Mill) cv. Arka Ashish. Plants were grown at elevated CO 2 [550 (EC 550 ) and 700 (EC 700 ) ppm of CO 2 ] in open top chambers. Increased assimilation rate, decreased stomatal conductance and transpiration rate were observed at elevated CO 2 (EC) concentrations. Reduced leaf osmotic potential and increased water potential were observed at EC compared with the control (380 ppm of CO 2 ) in flowering and fruiting stages. Lower total chlorophyll content was recorded at EC 700 . Plant height was significantly higher at EC 550 compared with EC 700 . Higher number of branches was observed at EC 700 as compared with plants grown at EC 550 and the control. Leaf area was lower at EC 700 compared with EC 550 but specific leaf mass was higher at EC 700 . Due to higher leaf dry mass and root dry mass, the plants grown at EC 700 exhibited higher total dry mass compared to EC 550 and the control. Increased number of flowers and fruits together with higher fruit set led to higher fruit yield at both EC concentrations. The highest yield increase was observed at EC 700 . The fruits showed a lower content of phenols, flavonoids, ferric reducing antioxidant potential, total soluble solids, and titratable acidity in plants grown at EC as compared with the control. The ascorbic acid content was high at both EC 700 and EC 550 . Carotenoids and lycopene content was low at EC 700 compared to higher content observed at EC 550 and the control.

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Tomato being sensitive to high temperature experiences mild to high temperature stresses under climate change conditions. To understand the response of tomato genotypes to mild temperature stress, a study was conducted in temperature gradient tunnel facility. The results revealed that across the genotypes studied, specific activity of antioxidant enzymes viz., superoxide dismutase (SOD), peroxidase (POX) and glutathione reductase (GR) increased significantly. Among the genotypes, increase in SOD activity was highest in cv. Arka Vikas, followed by IIHR 2195 and least in Abhinava. The GR activity was highest in Abhinava, followed by IIHR 2195 and least in cv. Arka Vikas. The mild temperature stress caused reduction in catalase (CAT) activity. The decrease in CAT activity and concomitant increase in POX activity was observed in cv. Arka Vikas. Low leaf water potential (W leaf ) and higher electrolyte leakage indicated that the membrane integrity was affected across the tomato genotypes even under mild temperature stress. Among the genotypes studied, cv. Arka Vikas showed greater activity of SOD and POX, higher membrane stability and least reduction in water potential under mild temperature stress.