Seasonal water acquisition and redistribution in the Australian woody phreatophyte, Banksia prionotes

Sap flows in the xylem of plant roots in response to gradients in water potential, either between soil and atmosphere (transpiration) or soil layers of different moisture content (termed hydraulic redistribution). The latter has the potential to influence water budgets and species interactions, but we lack information for all but a Few plant communities. We combined heat pulse measurements of sap flow with dye and isotope tracing techniques to gauge the movement of xylem sap within, and exudation from, roots of Banksia prionotes (Lindley). We demonstrated 'hydraulic lift' during the dry season and provide some evidence that extremely dry soils limit hydraulic lift. In addition we report difficulties posed by spiralled xylem tissue in roots for the application of heat pulse techniques. (C) 2000 Annals of Botany Company.