Contact Effects between Plant Roots and Soil Colloids

Abstract

The prevailing theories of mineral absorption by plants from soils are based on the concept of the soil solution, which is identified, essentially, with the nutrient soln. of the plant physiologist. The roots excrete carbonic acid into the liquid phase surrounding the soil particles. H-ions replace K+ from the surface of soil colloids, and the resulting KHCO3 is ready for intake by the roots. A theory for an additional method of mineral intake by plants from soils is here proposed, based on the phenomenon of ion interchange existing between 2 surfaces in contact. In view of the exptl. results obtained, it is believed that concepts of the mechanism of mineral absorption must be modified and extended. Ions of the same species may move both into and out of the root at the same time, the outgo being especially pronounced when the roots are in contact with colloidal systems. Accumulation and depletion are only net effects of ionic movements.