Hydraulic lift in a neotropical savanna

Abstract

1. We report hydraulic lift in the savanna vegetation of central Brazil (Cerrado). Both heat-pulse measurements and isotopic (deuterium) labelling were used to determine whether hydraulic lift occurred in two common species, and whether neighbouring small shrubs and trees were utilizing this water. 2. Both techniques showed water uptake by tap-roots and reverse flow of water in lateral roots. Roots transferred hydraulically lifted water to the soil, and small shrubs and trees neighbouring the labelled individuals were labelled by deuterated water. 3. Isotopic mass-balance equations and sap-flow measurements showed that water taken up by the central tap-root in each individual constituted only a small percentage of total flux of water through the treated plants. Mass-balance equations also indicated that small shrubs and trees neighbouring the treated plants utilized only a few thousandths of a per cent of the label. 4. The small proportion of water uptake by the tap-root of these two species may be limiting hydraulic lift in this system, unless sinker roots descending from lateral roots contribute to hydraulic lift.