Growth of lettuce plants (Lactuca sativa L.) under control of dissolved O₂ concentration in hydroponics

The effect of dissolved O₂ concentration on growth of lettuce plants (Lactuca sativa L.) was analyzed in hydroponics. The plants were grown for 7 days under different dissolved O₂ concentrations controlled at 0.01, 0.10 and 0.20 mM. Number of leaves was scarcely affected by the dissolved O₂ concentration, but leaf expansion was depressed at 0.01 mM where leaf water content became lower. Furthermore, the fresh and dry weights of leaves and roots were clearly reduced at 0.01 mM. On the other hand, difference in plant growth between 0.10 and 0.20 mM was scarcely found. These results suggest that growth of the lettuce plants at the lowest dissolved O₂ concentration of 0.01 mM is depressed through leaf turgor loss caused by decrease in root water uptake.