Effects of Elevated Carbon Dioxide on Ornamentals and Leafy Greens Grown in a Greenhouse

Carbon dioxide, being a major input for photosynthesis, plays an important role in plant production and propagation. To understand how elevated CO2 affects horticultural crops under greenhouse production, three studies were initiated: 1) pot production of ornamentals under varying irrigation and fertilizer levels, 2) propagation of an ornamental shrub, and 3) production of leafy greens in a hydroponics system. Each of the studies was conducted in a split-plot design in which one of the greenhouses was supplemented from morning to mid-day with CO2 to achieve an average concentration of 800 ppm and the other greenhouse was maintained under ambient conditions (400 ppm). The studies were conducted in spring and summer of 2016 and 2017.Container grown geranium and fountain grass showed greater growth rate under elevated CO2 in 10 or 15 cb irrigation than 5 cb when greater rate of fertilizer (6 or 9 g) was used. Elevated CO2 delayed flowering in geraniums but showed no effect in fountain grass. Since, species-specific response has been reported, grower needs to be cautious before CO2 supplementation if early flowering is desired. Propagation of Euonymus 'Moonshadow' through cutting in elevated CO2 had no effect in rooting percentage, reduced root number, and promoted early leaf senescence. However, 5000 ppm concentration of rooting hormone containing 1.5% IBA and 0.5% NAA showed greater root numbers compared to other treatment in ambient condition. Thus, elevated CO2 might not be effective in promoting rooting of Euonymus cuttings.Basil, lettuce, and Swiss chard produced in a hydroponics system under elevated CO2 were larger and achieved a marketable size earlier compared to similar plants grown under ambient conditions. However, elevated CO2 also resulted in leaf tipburn for lettuce, which might affect the market quality. On the other hand, leafy greens in elevated CO2 showed lower nitrogen (N) and phosphorous content compared to ambient condition. Since N is an essential component of many proteins and amino acid, this might affect the nutritional quality of crop. Thus, there is a necessity for more extensive studies with greater treatment combinations to produce nutritious crops in hydroponic at elevated CO2.Horticultur