A Manipulation of Air Temperature and Light Quality and Intensity can Maximize Growth and Folate Biosynthesis in Leaf Lettuce

We evaluated effects of different air temperature and light quality/intensity on growth and folate biosynthesis in leaf lettuce using a plant growth cabinet with light-emitting diodes (LEDs) combining red, green and blue (RGB) lights. Leaf lettuce was cultivated under combination conditions with 3 different air temperatures (20℃, 25℃ and 28℃) and 4 different light irradiations (photosynthetic photon flux density [PPFD] of 150 µmol m-2s-1 [P150]/RB, P150/RGB, P200/RB and P200/RGB) for 21 days. At the end of the cultivation, growth endpoints including edible portion weight, and folate contents were examined. The results demonstrated significant effects of air temperature and light quality and intensity on lettuce growth and folate biosynthesis. Under the optimal combination condition that we identified, 25℃ and P200/RGB, the edible portion weight and folate contents in leaf lettuce were 15-62％ and 83-137％ greater, respectively, compared to any light conditions at 20℃, an optimal temperature for conventionally growing leaf lettuce. Addition of green LED to red and blue LEDs maximized leaf lettuce growth and folate biosynthesis. Plant factory with optimal air temperature and light conditions utilizing RGB LED lights is a promising novel agriculture concept maximizing plant growth and critical nutrients such as folate.