ISHS Acta Horticulturae 633: XXVI International Horticultural Congress: Protected Cultivation 2002: In Search of Structures, Systems and Plant Materials for Sustainable Greenhouse Production
EFFECT OF SUPPLEMENTAL LIGHTING DURING THE PERIOD FROM MIDDLE OF NIGHT TO MORNING ON PHOTOSYNTHESIS AND LEAF THICKNESS OF LETTUCE (LACTUCA SATIVA L.) AND TSUKENA (BRASSICA CAMPESTRIS L.) |
| Authors: | N. Fukuda, S. Nishimura, Y. Fumiki |
| Keywords: | supplemental lighting, anatomical structure of leaf, chlorophyll, photosynthesis, lettuce, tsukena |
| Abstract:
Supplemental lighting during the period from middle of night to morning promotes growth of some leafy vegetables. In this study, we analyzed effects of light quality and light intensity of supplemental lighting on photosynthetic rate during daytime and leaf thickness of lettuce and tsukena. We used metal halide lamp (MH) and high-pressure sodium lamp (HPS) for lighting. Supplemental lighting was applied to the plant during the period middle of night 23:00 to 7:00. Three levels of light intensity were set as high (76 µmol m-2 s-1 (Photosynthetic photon flux (PPF)), low (16 μmol m-2 s-1) and control (0.0 μmol m-2 s-1). Shoot fresh weights of lettuce and tsukena under supplemental lighting with high light intensity were 53% and 37% higher compared with the control. However, there was insignificant difference between MH and HPS on shoot fresh weight. Supplemental lighting did not influence photosynthetic rate during daytime of lettuce. On the other hand, photosynthetic rate of tsukena under supplemental lighting was slightly lower than the control. Chlorophyll concentration per leaf area increased under supplemental lighting. Furthermore, the leaf thickness of lettuce increased 31-43% under supplemental lighting over control and, that of Tsukena was 32-38% higher over control. A dark green leaf color under supplemental lighting will result from the increase of leaf thickness. The increase of leaf thickness under supplemental lighting was higher under HPS compared to MH. On the contrary, supplemental lighting using MH increased leaf length and width of these crops more than HPS. It can be concluded that the supplemental lighting changes the leaf area and thickness of lettuce and tsukena. Additionally, the effect of supplemental lighting on leaf structure can be altered with the light quality of light source. On the other hand, adaptability of photosynthesis to extended photoperiod is higher in lettuce than Tsukena. | |
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