The Effects of Air Temperature on Yield and Phytochemical Content of Red Ssamchoo and Red Leaf Lettuce Grown in a Plant Factory

The consumption of leaf vegetables has been steadily increasing in Korea. Leafy vegetables are commonly used for “Ssam (vegetable wrap-up),” a popular way of eating fresh vegetables using fingers to wrap some cooked rice and seasoned condiments inside several layers of young vegetable leaves. Nutritional values and health benefits of leafy vegetables are well known. Studies on the growth and quality of major leaf vegetables like lettuce and bak-choi in the plant factory are available, but little work has been done on minor vegetables. This study was conducted to improve yield and quality of redssamchoo(Brassica koreana Lee var. red leaf) and red leaf lettuce (Lactuca sativa L.) grown in a plant factory where fluorescent lamps were used as an artificial light source. Seeds of redssamchoo and red leaf lettuce were sown in a peat-lite germination mix. Twenty-day old seedlings with roots being washed were anchored on a Styrofoam board and were grown hydroponically for 25 days under fluorescent light. Plants were exposed to three different daytime temperatures (20, 25 and 30 °C) which were being monitored with a sensor at 30 cm above the plant level. In all treatments, light intensity was maintained at 200 ± 30 μmol·m^-2s^-1, day length was 12/12 hr, and relative humidity was 50% to 80%. Electrical conductivity (EC) and pH of nutrient solution were 1.6 dS·m^-1 and 6.8–7.0, respectively, in all treatments. Increase in fresh weight was observed in redssamchoo at 30 °C, but red leaf lettuce was not significance. Photosynthetic capacity and vitamin C content of redssamchoo leaves were higher at 30 °C than other temperatures. In red leaf lettuce, photosynthetic capability was higher at 20 °C, while vitamin C content was higher at both 25 °C and 30 °C. Polyphenol and flavonoid content were higher at 20 °C in redssmchoo and red leaf lettuce. Hence, the optimum temperature appears to be 20 °C for phytochemical both redssamchoo and red leaf lettuce in the plant factory with fluorescent light.