Horticultural Science and Technology 원예과학기술지 ISSN:1226-8763(Print) 2465-8588(Online)

This study investigated the growth characteristics of lettuce (Lactuca sativa L. ‘Jeokchima’) according to the position of air anion treatment in a closed-type plant factory. The experimental conditions in the plant factory were as follows: fluorescent light with photoperiod of 16/8 h (light/dark), temperature of 20 ± 2°C and 50 ± 5% relative humidity. The nutrient solutions had a pH of 6.0 ± 0.5 and 1.8 ± 0.2 dS∙m^-1 electrical conductivity (EC). The plants were transplanted into the factory from a plastic bed and exposed to air anion treatment from three different positions (sideward, upward, and downward) for 4 weeks. The growth characteristics of lettuce (leaf length and width, shoot fresh weight and shoot dry weight, leaf area, chlorophyll content, antioxidant capacity, and total phenol content) were measured at 3 weeks and 4 weeks. After 4 weeks in the downward anion treatment, lettuce leaves were 14% longer and 21.5% wider than the leaves of the control plants. Furthermore, the shoot fresh weight of lettuce grown in the downward anion treatment was 37.1% greater than that of the control lettuce. Similar results were observed for shoot dry weight. Out of the 3 positions of anion generation, the downward position produced lettuces with the greatest leaf area. The chlorophyll content of lettuce decreased during all of the anion treatments. The antioxidative activity and total phenol content of lettuce decreased during the downward anion treatment. These results imply that the optimum position of anion treatment for increasing lettuce production in closed-type plant factories is the downward position.