Light intensity and photoperiod influence the growth and development of hydroponically grown leaf lettuce in a closed-type plant factory system

Effect of light provided by various light intensities combined with different photoperiods on the growth and morphogenesis of lettuce (Lactuca sativa L.) 'Hongyeom Jeockchukmyeon' in a closed-type plant factory system were evaluated in this study. Four light intensity treatments, i.e., 200, 230, 260, and 290 mu mol.m(-2).s(-1) PPFD, provided from light-emitting diodes (LEDs), with a combination of three different photoperiods 18/6 (1 cycle), 9/3 (2 cycles) or 6/2 (3 cycles) (light/dark) were used. The combination of 290-9/3 (light intensity-photoperiod) showed the highest plant height and fresh shoot weight, while plants grown at 290-18/6 exhibited the greatest root fresh weight, leaf dry weight, and longest root length. The greatest leaf width, maximum number of leaves, and greatest root dry weight were observed in the treatment combination of 290-6/2. Anthocyanin content was found to be highest in the 290-6/2 and lowest in the 200-6/2 treatment, whereas chlorophyll fluorescence was observed to be highest in the 260-6/2 and the lowest in the 290-9/3 treatment. Our data showed that providing a high light intensity of 290 mu mol.m(-2).s(-1) PPFD with a shorter photoperiod of 6/2 (light/dark) resulted in good plant growth and development of lettuce, whereas growth at light intensities of 230 or 260 mu mol.m(-2).s(-1) PPFD with longer photoperiods of 18/6 and 9/3 (light/dark) resulted in good growth as well as higher photosynthetic capacity.