Transverse hydraulic redistribution by a grapevine

Root hydraulic redistribution has been shown to occur in numerous plant species under both field and laboratory conditions. To date, such water redistribution has been demonstrated in two fundamental ways, either lifting water from deep edaphic sources to dry surface soils or redistributing water downward (reverse flow) when inverted soil Ψ_s gradients exist. The importance of hydraulic redistribution is not well documented in agricultural ecosystems under field conditions, and would be important because water availability can be temporally and spatially constrained. Herein we report that a North American grapevine hybrid (Vitis riparia × V. berlandieri cv 420 A) growing in an agricultural ecosystem can redistribute water from a restricted zone of available water under a drip irrigation emitter, laterally across the high resistance pathways of the trunk and into roots and soils on the non-irrigated side. Deuterium-labelled water was used to demonstrate lateral movement across the vine's trunk and reverse flow into roots. Water redistribution from the zone of available water and into roots distant from the source occurred within a relatively short time frame of 36 h, although overnight deposition into rhizosphere soils around the roots was not detected. Deuterium was eventually detected in rhizosphere soils adjacent to roots on the non-irrigated side after 7 d. Application of identical amounts of water with the same deuterium enrichment level (2%) to soils without grapevine roots showed that physical transport of water through the vapour phase could not account for either downward or transverse movement of the label. These results confirmed that root presence facilitated the transport of label into soils distant from the wetted zone. When deuterium-labelled water was allowed to flow directly into the trunk above the root–trunk interface, reverse flow occurred and lateral movement across the trunk and into roots originating around the collar region did not encounter large disproportionate resistances. Rapid redistribution of water into the entire root system may have important implications for woody perennial cultivars growing where water availability is spatially heterogeneous. Under the predominantly dry soil conditions studied in this investigation, water redistributed into roots may extend root longevity and increase the vines water capacitance during periods of high transpiration demand. These benefits would be enhanced by diminished water loss from roots, and could be equally important to other cited benefits of hydraulic redistribution into soils such as enhancement of nutrient acquisition.