RELATION OF H-ION CONCENTRATION OF TISSUE FLUIDS TO THE DISTRIBUTION OF IRON IN PLANTS

Abstract

Although iron is an essential element for plant growth, it is not always present in an available form for assimilation by the plant. Factors influencing the availability of iron are not well understood. Previous investigations of the iron problem have dealt mainly with a study of the external medium in which the plants were grown, with less emphasis attached to the study of the conditions existing within the plants themselves. Patten and Main (18) found that iron was precipitated from solution in varying degrees from pH 3.5 to 6.0, practically all being precipitated at 6.0 and above, thus rendering it unavailable for absorption by the plant. This was also brought out by Hopkins and Wann (10). They found difficulty in growing plants in a medium of pH 6.0, due to the fact that iron was removed by adsorption on calcium phosphate which gradually precipitated as the solution became alkaline, a physical chemical effect capable of influencing iron availability within the plant as well as in culture media. The fact that lack of available iron is not entirely due to the conditions existing in the culture media may be shown by reference to the work of Appel (2). He found that buckwheat plants were less sensitive to changes in reaction of culture media than were corn plants, corn requiring much more iron than buckwheat. Little difficulty, therefore, was experienced in growing buckwheat without chlorosis in solution cultures in which corn suffered from lack of available iron. After a study of the internal conditions existing within the plant, presented in the following pages, an explanation of this phenomenon may be attempted. Loehwing (13) has reported that plants grown in a medium high in lime display peculiar iron immobility characterized by copious precipitation in the roots. He states that the lime reduces the sap acidity to the point of interference with internal iron mobility. Lime injury involving chlorosis has been reported for corn by Maze (16), for pineapples by Gile (5), for rice by Gile and Carrero (6), for pears by Milad (17), and for citrus fruits by Lipman (22). In addition to the work cited, some work has been reported on the H-ion concentration of tissue fluids. Haas (8) made studies of actual and total acidities and of the total alkalinity of a number of plants of agricultural importance, together with a study of the influence of liming the soil upon 103