Hydraulic redistribution of soil water by tree roots.

MEINZER FREDERICK C., BROOKS J.R., SCHOLZ FABIÁN G., BUCCI SANDRA J., GOLDSTEIN G.

Cairns Australia

Simposio; 3er International Canopy Conference; 2003

Deeply rooted trees and other plants can hydraulically lift water from deep, moist soil horizons several meters below the soil surface to drier portions of the soil profile where it is released into the soil. The process is thought to be largely passive, requiring only a water potential gradient from moist soil layer through the root xylem to dry soil layers, and a relatively low resistance to reverse flow from the roots. Although the direction of water movement is typically upward, towards drier, shallow soil layers, recent measurements of sap flow in taproots and lateral roots of trees have demonstrated that roots can also redistribute water either downward or laterally from moist surface soils to drier regions of soil. Now that more than 60 cases of hydraulic redistribution have been reported, there is reason to expect that its existence is widespread wherever conditions are conducive to its occurrence. However, the magnitude of hydraulic redistributing and its significance for individual tree and ecosystem-lever water fluxes has been debated. Here we discuss results of recent and ongoing studies of the magnitude and timing of hydraulic redistribution in a range of ecosystems dominated by trees and other woody plants. We show that in vegetation subjected to prolonged seasonal drought, hydraulic redistribution can substantially retard the rate of drying in the upper portion of the soil profile where fine roots are located, and that hydraulically redistributed water can be utilizes by neighboring plants.