The Comparison of Constant and Dynamic Red and Blue Light Irradiation Effects on Red and Green Leaf Lettuce

In this study, we sought to evaluate and compare the effects of constant and dynamic lighting on red and green leaf lettuce (Lactuca sativa L. Red Cos and Lobjoits Green cos) cultivated in a controlled environment. Plants were illuminated with the combination of red 662 and 638 nm, blue 452 nm, and far-red 737 nm at 16 h photoperiod and constant daily light integral (DLI) of each component. Five constant or dynamic lighting treatments were performed: (BR) constant flux of both B452 and R662; (B*R) constant flux of R662, but the DLI of B452 condensed in 8 h in the middle of photoperiod doubling the PPFD of blue light; (BR*) constant flux of B452, but the DLI of R662 light condensed in the middle of photoperiod; (BdynR) constant flux of R662, but the flux of B452 varies in the sinusoidal profile during 16 h photoperiod, imitating diurnal increase and decrease in lighting intensity; and (BRdyn) constant flux of B452, but the flux of R662 varies in sinusoidal profile. The lettuce's response to dynamic lighting strategies was cultivar specific. Dynamic lighting strategies, mimicking natural lighting fluctuations, did not have a remarkable effect on photosynthesis and antioxidative parameters, but the dynamic flux of blue light component had a pronounced effect on higher macro and microelement contents in lettuce leaves.