Time dependence of the growth promotion of cucumber seedlings by blue-lighting during morning twilight

摘要

Cucumber (Cucumis sativus L. cv. Naoyosi) plants were grown hydroponically at air temperatures of 28/24 deg C (D/N) and 300 #mu#mol m~(-2) s~(-1) PPF, in a walk-in type growth cabinet equipped with 3-band fluorescent lamps. For 0, 5, 30 or 120 rain, blue-lighting at 30 #mu#mol m~(-2) s~(-1) in PPF was applied daily just before the 14 h photoperiod (morning twilight). Growth parameters were measured after 12 and 24 d of treatment. After 13 d of treatment, the stomatal conductance, transpiration rate and net photosynthetic rate were measured under 3-band fluorescent lamps at a PPF of 200#mu#mol m~(-2) s~(-1). At 17-19 d of treatment, changes in net photosynthetic rate affected by blue-light were measured continuously for 30 min. Fresh and dry weight, leaf area, plant height and stem diameter of plants were the greatest with bluelighting for 5 min. The stomatal conductance, transpiration rate and net photosynthetic rate after 13 d of treatment were greatest in the plants grown with supplemental blue-light for 5 min. The net photosynthetic rate for 5 rain treatment increased by 60% as compared with that of control plants grown without lighting. Continuous measurements showed net photosynthetic rate to rise and the high level was maintained with 5 min blue-lighting treatment. These results indicate that the promotion of plant growth by blue-lighting during morning twilight is dependent on the lighting time. For cucumber seedlings, blue-lighting for 5 min was more effective for growth than for 30 and 120 min.