日の出前の青色光による補光時間がキュウリ苗の成長促進におよぼす影響

Abstract

Cucumber (Cucumis sativus L. cv. Naoyosi) plants were grown hydroponically at air temperatures of 28/24°C (D/N) and 300μmol m-2 s-1 PPF, in a walk-in type growth cabinet equipped with 3-band fluorescent lamps. For 0, 5, 30 or 120 min, blue-lighting at 30 μmol 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 μmol 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 min 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.