The Effects of Partial Root-zone Drying on Water Uptake Between the Drying and Wetting Zones

Partial root-zone drying (PRD) is an irrigation method that manipulates plant chemical and hydraulic signals from the roots to the leaves to close stomata and increase water use efficiency (WUE). The roots are split into two "zones", one zone is allowed to dry and the other zone is irrigated. Roots in the drought-stressed zone may produce ABA and/or send a hydraulic pressure signal to trigger abscisic acid (ABA) production in the shoots. Accumulation of ABA in the shoots signals the stomata to close. The dynamics of water uptake between the drying and wetting zones has not been separated as to its affect on overall transpirationkA dwarf tomato variety, ‘Micro-Tina’ (Lycopersicon esculentum Mill) was grown from seed, then root systems were split and placed in two 10-cm pots. Soil moisture sensor probes were placed in each pot and connected to a data logger.  Irrigation was controlled based on the average substrate water content of one plant (one sensors in each of the two pots). An irrigation valve opened when the average reading from these two sensors dropped below 40% (v/v). Each plant was watered with two 4 L·h^-1 emitters. Individual pots were placed on load cells to measure water uptake and transpiration from each half of the root system. Three treatments,(v/v): 40% (control), 25%, and 15%, were applied. In control plants, each pot had one emitter. The two drought stress treatments were implemented by placing both drip lines into one pot and allowing the “drying side” to reach the desired volumetric water content (VWC), after which the two lines were switched to the other pot. Placing both water lines in one pot ensured that all plants received equal amounts of water. Water uptake in the “irrigated side” increased, adjusting for the decreased water uptake from the “drying side” The 25% and 15% VWC treatments appeared to reduce leaf photosynthetic rate and stomatal conductance. This data suggest that 15% and 25% VWC treatments reduced transpiration rates while both root sides continued to uptake water.