Contact Exchange and Its Importance in the Nutrition of Plants

After reading this article you will learn about the contact exchange and its importance in the nutrition of plants.

Contact exchange is defined as the phenomenon by which the exchange takes place between ions held on the surfaces of solid-phase particles (solid-solid exchange) and that it does have to occur via the liquid phase.

For an example, the exchange takes place between ions attached to the surface of root hairs (e.g. H⁺ ions) and ions held on the surface of clays and organic matter in soils (because of the intimate contact that exists between roots and soil particles).

Clay and plant roots both have CEC properties. Ions are believed to be held at certain spots or sites on both roots and colloidal soil surfaces. The ions held by electrostatic or van der Waals forces at these sites tend to oscillate within a certain volume.

When the oscillation volumes of two ions overlap, the ion exchange takes places. In this way, calcium (Ca²⁺) ion on a clay surface could then presumably be adsorbed by the root and utilized by the plant.

There is uncertainty about the importance of contact exchange in the nutrition of plants. It has been estimated that roots may grow to only about 3% of the available nutrients in soils. There is a strong possibility; however, that the root-soil gap is eliminated by the mucilaginous gel that can occur around root surfaces. This mucigel could serve as a contact complex since it is known to be penetrated by soil particles.

The presence of ectotrophicmycorrhiza, a symbiotic association between fungi and the roots of plants, enhances the uptake of several plant nutrients, particularly phosphorus. The hyphal threads of mycorrhizal fungi act as an extension of plant root systems, resulting in greater exploitation of soil in the root zone. So it is possible that contact exchange becomes more significant when mycorrhiza is active.