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Carbon dioxide (CO2) concentration is reported to be the most important climate variable in greenhouse production with its effect on plant photosynthetic assimilation. A greenhouse study was conducted using a nutrient film technique (NFT) system to quantify the effect of two different levels of CO2 (supplemented at an average of 800 ppm and ambient at ~410 ppm) on growth and nutritional quality of basil (Ocimum basilicum L.) 'Cardinal', lettuce (Lactuca sativa L.) 'Auvona', and Swiss chard (Beta vulgaris L.) 'Magenta Sunset' cultivars. Two identical greenhouses were used: one with CO2 supplementation and the other serving as the control with an ambient CO2 concentration. The results indicate that supplemented CO2 could significantly increase the height and width of hydroponically grown leafy greens. Supplemented CO2 increased the fresh weight of basil 'Cardinal', lettuce 'Auvona', and Swiss chard 'Magenta Sunset' by 29%, 24.7%, and 39.5%, respectively, and dry weight by 34.4%, 21.4%, and 40.1%, respectively. These results correspond to a significant reduction in Soil Plant Analysis Development (SPAD) and atLEAF values, which represent a decrease in leaf chlorophyll content under supplemented CO2 conditions. Chlorophyll, nitrogen (N), phosphorus (P), and magnesium (Mg) concentrations were generally lower in plants grown in supplemented CO2 conditions, but the results were not consistent for each species. Supplemented CO2 reduced tissue N concentration for basil 'Cardinal' and lettuce 'Auvona' but not Swiss chard, while Mg concentration was reduced in supplemented CO2 for Swiss chard 'Magenta Sunset' only. In contrast, Fe concentration was increased under supplemented CO2 for basil 'Cardinal' only. These findings suggest CO2 supplementation could increase yield of leafy greens grown with hydroponics and have varying impact on different mineral concentrations among species. [ABSTRACT FROM AUTHOR]