Tomato plants (Solanum lycopersicum L. 'Grandia') were grown in a deep-water culture system, with varying oxygen (O2) concentrations in the nutrient solution. Oxygen depletion of the nutrient solution by the plants as a function of distance from an aeration point could be best described by a concave exponential curve. Increase of branch length, number of side branches and number of flowers per plant were plotted against time and found to produce different types of curves (exponential, logarithmic and linear, respectively). The slopes of the best-fit functions of these curves were linearly correlated to the O2 concentration in the hydroponic medium. The effect of O2 concentration in the nutrient solution on the fresh and dry weights of roots and shoots was positive and exponential. There were no significant changes in response to O2 in the ratios of root to shoot fresh and dry weights, or of the ratios of dry to fresh weights of roots or shoots. Fruit production increased linearly with O2 concentration around the roots. It was concluded that tomato plants in deep-water culture do not reach the theoretical maximum rate of O2 uptake into the roots.
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