Effect of Greenhouse CO₂ Supplementation on Yield and Mineral Element Concentrations of Leafy Greens Grown Using Nutrient Film Technique

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.