Lettuce is the most cultivated leafy vegetable under vertical farming due to its short growth period and stable market demand. However, lettuce production in those systems often faces challenges such as unequal temperature inside cultivation room and benches, which causes uneven growth, leading to cultivation delays and yield loss. In this study, we investigated the effect of constant air flow on lettuce production in vertical farming to observe changes in morphology and yield. The aim of this study was to improve leaf lettuce production in vertical farms. Leaf lettuces were grown at Advanced Plant Factory Research Center, Meiji university under temperature of 22°C, relative humidity of 60%, under white LED light at a PPFD of 140–200 µmol·m⁻²·s⁻¹ for 16 hours. The hydroponic solution was supplied to the seedlings by the deep flow technique at an EC of 1.6 dS·cm⁻¹, pH of 6.0±0.5. For the air flow treatment, air tubes were placed above the seedlings, a constant wind speed of 0.1-0.2 m/s for 24 hours was supplied to seedlings. At 10, 20, and 30 days after transplanting (DAT), lettuces from both the control and air flow treatment groups were selected for stomata evaluation using a non-destructive equipment. At 30 DAT, yield evaluation, including fresh weight, leaf count, and morphology change such as leaf thickness, was also conducted. We found that the constant air flow treatment increased the fresh weight and leaf count of the lettuces. Furthermore, an increase in leaf hardness was observed. Moreover, we found that the number of stomata tended to be higher when the fresh weight was greater. This tendency was particularly strong in the air flow group which proved that it improved the growth and morphological characteristics of lettuce, suggesting its potential for enhancing vertical farming productivity.
