Tracing water uptake by jarrah (Eucalyptus marginata) trees using natural abundances of deuterium

Seasonal change in the delta(2)H content of water from twig sap, soil, rainfall and groundwater were measured to determine the water sources accessed by jarrah (Eucalyptus marginata) trees at three sites in Western Australia with differing soils and depths to water table. During winter and spring the main contributor to the water uptake of the trees was stored water in the surface layers of the soil replenished by predominantly winter rainfall. With the onset of summer drought jarrah became more reliant on water from deeper down the profile. There was no clear evidence that jarrah could tap water from groundwater more than 14 m deep in deep sands. Defining the source of water for trees in deep lateritic soils using stable isotopes is hampered by the uniform deuterium profiles down most of the unsaturated zone and into the groundwater. There was a limited response in the delta(2)H values of sapwater in twigs to changes in the delta(2)H of the upper layers of the deep sand following input of rainfall in autumn. The damped response was related to the small variation in the delta(2)H composition of rainfall in most events during the year and the mixing in the tree of water extracted from different locations in the soil profile.