Effect of Dissolved O2 Levels in a Nutrient Solution on the Growth and Mineral Nutrition of Tomato and Cucumber Seedlings

The root systems of tomato (Lycopersion esculentum Mill., cv. Hausu-Momotaro) and cucumber (Cucumis sativus L., cv. Sharp I) seedlings were subjected to four different dissolved O2 (DO) levels in nutrient solution for 8 days under artificial light conditions. The DO levels were kept constant at 1, 2, 4 and 8 ppm, and the solution temperature was controlled at 22 and 30℃ for tomato and at 25 and 33℃ for cucumber. 1.Growth of tomato plants at 1 and 2 ppm DO was inferior to that at higher DO levels, irrespective of solution temperatures. 2.Growth of cucumber plants was slightly retarded even at 1 ppm when the solution was held at 25℃. At 33℃, the growth was significantly inhibited at 1 and 2 ppm DO levels, similar to tomato. These results suggest that to control the vegetative growth of young plants in DFT by means of the DO level, lowering the DO level to about 2 ppm is appropriate for tomato. For cucumber, however, it seems necessary to lower the DO level well below 1 ppm to control effectively its vegetative growth. Possible causes of the difference in the tolerance to low DO levels between tomato and cucumber are discussed as to the morphologocal changes and iron-induced oxygen radical formation in the roots. 栄養生長と生殖生長のバランスが崩れて過繁茂になりやすい果菜類の湛液水耕での生長調節をDOによって行うためには，一定レベルの低DOに対する作物の生長および生理的反応を明らかにする必要がある．そこで，トマト‘ハウス桃太郎’とキュウリ‘シャープI’の幼植物，DOを1，2，4，8ppm に調節した湛液水耕(液温は，トマトでは22℃と30℃とし，キュウリでは25℃と33℃とした)で8日間栽培し，生育と葉および根の無機成分濃度を調査した．その結果，トマトは，液温にかかわらず2ppm以下で生育が不良になり，葉身の含水量や無機成分濃度が低下した．キュウリでも液温が33℃の場合は2ppm以下で生育が制御されたが，25℃の場合は1ppmでもほぼ正常に生長し，葉身含水率や無機成分濃度も影響を受けなかった．以上の結果から，湛液水耕でDOによって栄養生長を調節する場合，トマトでは2ppm目安にすればよいと思われるが，キュウリでは1ppm以下に下げる必要があると判断される