PARTIAL ROOTZONE DRYING: CHEMICAL SIGNALLING THEORY AND IRRIGATION PRACTICE
Soil drying stimulates root production of chemical signals such as ABA, which are transferred via the xylem to the shoots to restrict water use and limit vegetative growth. Partial rootzone drying (PRD) is a deficit irrigation (DI) technique that aims to exploit this root-to-shoot signalling by alternately irrigating only one side of the crop row at a time and allowing the other to dry the soil. Adoption of PRD (in favour of conventional DI where the entire rootzone is irrigated) requires evidence that it induces beneficial agronomic and physiological responses that differ from DI, when the same volumes of water are applied. Although this occurs in some cases, equivalent yield in other studies suggests that chemical signalling during PRD has not been optimized. To investigate the contribution of different parts of the root system to ABA signalling during PRD, tomato root systems were allowed to grow into two halves of a split-pot and water uptake from different parts of the roots system determined via continuous soil moisture monitoring. Excessive soil drying (which stopped sap flow from roots in drying soil) resulted in xylem ABA concentration ([X-ABA]leaf) of PRD plants being dependent on the soil water status of the irrigated pot. Alternating the wet and dry root systems restored sap flow through the previously dried root system, causing a transient (<24 h) increase in [X-ABA] leaf, which has also been detected in some field studies. Increasing the root mass exposed to drying soil magnified the effects of PRD on leaf elongation and leaf ABA concentration, independently of leaf water potential. Exploiting this theoretical knowledge to enhance ABA signalling in the field may be hindered by only being able to control soil moisture in a limited part of the rootzone, due to lateral and vertical root system proliferation.
Dodd , I.C., Egea , G., Martín-Vertedor, A.I., Romero, P. and Pérez Pérez, J.G. (2011). PARTIAL ROOTZONE DRYING: CHEMICAL SIGNALLING THEORY AND IRRIGATION PRACTICE. Acta Hortic. 922, 67-74
abscisic acid, deficit irrigation, root-to-shoot signalling, soil moisture heterogeneity, root distribution, xylem sap