ISHS Acta Horticulturae 689: VII International Symposium on Grapevine Physiology and Biotechnology
PHYSIOLOGICAL MECHANISMS INVOLVED IN THE PRODUCTION OF NON-HYDRAULIC ROOT SIGNALS BY PARTIAL ROOTZONE DRYING - A REVIEW |
| Author: | B.A. Bravdo |
| Keywords: | water use efficiency, stomatal conductance, root signals, partial root drying, tomato, grapevine |
| Abstract:
Parallel to the progress in irrigation methods and technology during the past few decades, there is interest in using physiological mechanisms of plants to assist in irrigation management. Scheduling irrigation with drip systems consists of frequent irrigations applied only to part of the root system as well as non-uniform soil water distribution. The dynamic nature of such systems encounters difficulties in utilization of traditional parameters such as “permanent wilting point”, “field capacity” and “available water”. When various parts of the root system are subjected to a wide range of soil water potentials, root to root transfer of water and minerals is an important fundament of the mechanism involved. Irrigating only a part of the root system does not change the basic pattern of root distribution and various root types such as feeding rootlets and supporting roots are still formed according to the genetic trait of each variety. There is, however, an intensive development of small diameter rootlets with a large surface area and a lot of active root tips in the soil beneath the drippers. Such intensive root systems enhance the uptake of water and minerals nutrients, as well as intensive production of plant growth regulators (PGR); root signals. Cytokinins, abscisic acid (ABA) and gibberellins are the major PGRs formed in the root tips and their transport to various parts of the canopy are involved in various physiological processes. The ability to control soil water potential of various parts of the root system by different types of irrigation systems has lead researchers to try and affect the production of root signals and thereby increase water use efficiency, as well as canopy architecture and fruit bud differentiation. The partial rootzone drying (PRD) method, where irrigation is alternated from one to the other side of the plant every two weeks, was reported to increase ABA production, reduce cytokinin production, and raise the xylem pH by drying roots. A non-hydraulic regulation of stomatal conductance, shoot, leaf and fruit growth as well as increased water use efficiency, was measured in split root experiments conducted in containers or root restricting compartments. Such results have never been reported for PRD open field experiments. It may well be that an absolute control of root drying is essential for obtaining such non hydraulic effects and drip irrigation under field conditions does not provide means for drying sufficient portion of the roots for inducing concomitant non hydraulic effects. | |
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