PARENT SESSION
Tuesday, August 8, 5:00-6:30 pm
Poster Session 11 - Plant physiological ecology
Exhibit Hall, Ballroom Level, Cook Convention Center
Stem-mediated hydraulic redistribution of soil water in semi-arid Eucalyptus trees.
Bleby, Timothy*,1, 2, Burgess, Stephen2, 3, 1 Duke University, Durham, NC2 The University of Western Australia, Perth, WA, Australia3 Cooperative Research Centre for Plant-Based Management of Dryland Salinity, Perth, WA, Australia
ABSTRACT- Many plants can act as equalizers of soil moisture through the phenomenon of hydraulic redistribution (HR), defined as the passive movement of water from patches of wet soil to dry soil via plant roots. While the occurrence of HR has been well documented and its ecological implications are significant, the magnitudes, pathways and hydraulic resistances of this process remain poorly understood. The aim of this study was to understand HR dynamics in large trees that do not have obvious tap roots or specialized root 'junction zones' at the base. We present detailed sap flow measurements from the roots and stems of semi-arid Australian Eucalyptus trees showing that following rain, water is rapidly transferred between lateral roots, at rates much faster than previously described for other types of HR. We also show that sap flow in the outer xylem of the stem is highly sectored around the circumference, and this is clearly associated with 'lateral HR'. Nocturnal patterns of sap flow in the stem following rain consist of large positive flows (towards the leaves) in sectors on one side of the tree, large negative flows (towards the roots) on the other side of the tree, and sectors that grade smoothly from positive to negative via neutral-flow in between. These results suggest that: 1) stem tissues can act as a go-between during HR, permitting water exchange among lateral roots that are otherwise poorly-connected; and 2) this exchange very likely involves considerable circumferential sap flow around the stem in addition to positive and negative axial flows.
Key words: hydraulic redistribution, semi-arid woodlands, Eucalyptus