Factors Affecting Root Exudation

Publisher Summary The absorption and desorption of substances that are extremely diverse in molecular size and in physicochemical and biological properties occur at the root surface. Substances (other than water) which are released from plant surfaces have been termed as “exudates” by many investigators, regardless of whether their appearance on the surface is the result of passive or active transport. In regions of the plant other than the root, exudation may occur from special structures called “glands,” but in roots no glands have ever been demonstrated. This chapter brings together the body of information pertaining to the quantitative and physiological aspects of root exudation. It points out the ways the development of techniques for axenic culture of whole plants may aid this kind of research. Exudation from roots of organic substances is affected by a variety of factors, including soil water stress, temperature, light intensity, the age and species of plant, mineral nutrition, soil microorganisms, the degree of anaerobiosis, and the foliar application of chemicals. Compounds exuded, such as amino acids and carbohydrates, are involved in the ecological succession of microorganisms colonizing roots and in interactions with adjacent plants. The implications in the control of plant root diseases, in control of weeds, and in mineral nutrition are unknown. The development of new techniques and simplified systems is needed to establish the causes of plant root diseases and effect the relationships and interactions in the soil-microbial-plant root ecosystem.