MOISTURE ABSORPTION BY PLANTS FROM AN ATMOSPHERE OF HIGH HUMIDITY

Abstract

The physics of water movement in the soil has been the subject of a great deal of investigation. The role of the plant in soil moisture and soil moisture plant relationships has been studied less intensively. Under arid and semi-arid conditions plants are often subjected to tensions extending over a wide range of soil moisture percentages, and there is evidence that the plants themselves often contribute to their own survival under moisture stress by absorption and exudation of inoisture. BREAZEALE (1), and BREAZEALE and CRIDER (2) have shown that a plant can absorb water and transport it from one zone of low tension to one of high tension if a part of its root system is presenit in both zones. BREAZEALE and McGEoRGE (3) have shown that this phenomenon can be used to determine the wilting percentage of the soil-that is, the equilibrium occurring when the water-retaining forces of the soil equal the water-absorbing forces of the plant roots. In the semi-arid southwest summer crops exhibit a distinctly different growth response to rain, which is accompanied by a high humidity, than they do to an irrigation which is accompanied by a low humidity. Winter crops which are grown under more favorable atmospheric conditions with respect to humidity and temperature show less moisture stress than summer-grown crops. It is of interest, in this connection, that along the coast of California, where fogs exist, some crops are grown without irrigation and with only a few inches of rainfall. The observations of BRIERLEY (4) are of interest in this connection. He noted an increase in size of raspberries following a very light shower during which only enough rain had fallen to wet the leaves. The soil was not wetted. He postulated that the increase in size of berries, followinlg such a light shower, might be due to absorption of water by the leaves. In order to study this further, he selected leaves from a large number of different plants and allowed them to wilt after sealing the stem with paraffin. When these wilted leaves were immersed in water they recovered turgidity. While it is recognized that a low transpiration rate reduces the moisture stress, the question of water intake through the leaves is pertinent. The following experiments were conducted to study water intake through leaves when the above-ground part of the plant is subjected to fog or highly humid atmospheres.