Mineral nutrition and the water relations of plants

Summary

The rates of water uptake and transpiration of young plants of tomato, sweet corn, lettuce, and spring wheat were measured when they were transferred from ordinary culture solution into nutrient solutions of different concentrations or into mineral-free water.

Uptake per unit fresh weight of root and transpiration per unit fresh weight of shoot and per unit leaf area were markedly lower in mineral-free water than in nutrient solutions with OPs of 0.1 to 0.5 atm. The reduction did not appear until a day or more after the plants were placed in mineral-free water. For a few hours after transfer, uptake from mineral-free water was usually higher than from nutrient solutions.

The effect of mineral-free water was not associated with the reduced OP of the medium, lack of aeration or low pH. Mineral-free water reduced the stomatal aperture and the water content of the shoots, indicating that mineral nutrients played an important role in the water economy of the plants.

It was concluded the reduced uptake and transpiration in mineral-free water were not merely direct consequences of reduced growth and that there is a specific requirement for mineral salts if maximum water uptake and transpiration are to occur.

At night, mineral-free water usually exerted a large effect on uptake, including the complete suppression of guttation. In the daytime, with a few exceptions, the higher the radiation intensity the greater was the effect of mineral-free water on uptake. These results suggest that mineral-free water affects both active water transport arising from root pressure and passive transport in the transpiration stream.

It is suggested that some of the conflicting results in the literature may have been caused by differences in the radiation conditions or by differences in the duration of the experiments.