The manipulation of grapevine leaf gas exchange through irrigation management

Abstract

During the past ten years the Australian winegrape industry has experienced a period of massive expansion fuelled by demand for high quality, reasonably priced wines in world markets. Since 1987 the area planted to grapevines has increased from 60,000ha to the current area of 146,000ha. This expansion has occurred in a climate of decreasing availability of water for irrigation and an increase in its cost. There is therefore considerable pressure on the winegrape industry to increase its efficiency of water use. Grapevines retain tight control over stomatal conductance, which is very responsive to relatively small reductions in soil water availability. We have been able to exploit this responsiveness in developing a novel irrigation strategy which increases the efficiency of water use by inducing partial stomatal closure while retaining sufficient assimilation capacity to maintain the yield potential of the vine. The strategy requires that roots are simultaneously exposed to wet and dry soil. Changes in root and shoot abscisic acid (ABA) suggests that ABA, produced in the drying roots, is primarily responsible for reduced stomatal conductance. The effects of this partial root drying on leaf gas exchange and on the transport of ABA from root to shoot can be reproduced by exogenous application of a low concentration of ABA to part of the root system. Furthermore, partial root drying also changes the concentration of zeatin and zeatin riboside in roots and their transport to the shoot. Exogenous application of cytokinin to grapevines undergoing partial root drying overcomes the effect on leaf gas exchange. We conclude that the efficiency of water use in vineyards can be significantly improved through strategic irrigation management and that this is driven by hormonal changes induced in drying roots.