Effects of Temperature Variations during Light Period on Growth and Tipburn Incidence of Hydroponic Leaf Lettuce Grown under Artificial Lighting

This study identified the effects of temperature variations during the light period on the growth of hydroponic leaf lettuce grown under artificial lighting. The temperature during 16-h light period and 8-h dark period was set at 23℃ and 18℃, respectively, as a control. In experiment 1, the temperature was quickly risen (QR) at the start of the light period (SL), kept at 23℃ during the first half of light period, and then slowly decreased during the second half of light period, as QRSL treatment. In experiment 2, the temperature was increased gradually during the first half of light period, kept at 23℃ during the second half of light period, and then quickly dropped (QD) at the end of the light period (EL), as QDEL treatment. The temperature during the dark period was set to 18℃ in both treatments. Both treatments increased fresh and dry weights of shoot. The QRSL treatment increased the growth rate and decreased the tipburn incidence. Meanwhile, the QDEL treatment decreased the growth rate because of the tipburn occurrence before harvesting. It was possible that these effects of temperature variations include the effects of vapor pressure deficit fluctuations since humidity varied with temperature.