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

Abstract

The root systems of tomato (Lycopersicon 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°C for tomato and at 25 and 33°C 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°C. At 33°C, 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 morphological changes and iron-induced oxygen radical formation in the roots.