SOURCES OF WATER USED BY RIPARIAN EUCALYPTUS-CAMALDULENSIS OVERLYING HIGHLY SALINE GROUNDWATER

Water sources of Eucalyptus camaldulensis Dehn. trees were investigate d on a semiarid floodplain in south-eastern Australia. The trees inves tigated ranged in distance from 0.5 to 40 m from a stream, with electr ical conductivity 0.8 dS m-1, and grew over groundwater with electrica l conductivity ranging from 30 to 50 dS m-1. The sources of water bein g used by the trees were investigated using the naturally occurring st able isotopes of water and measurements of soil water potential. Xylem water potential and leaf conductance were also examined to identify t he trees' response to using these sources of water. Trees at distances greater than about 15 m from the stream used no stream water. The tre es used groundwater in summer and a combination of groundwater and rai n-derived surface-soil water (0.05-0.15 m depth) in winter. In doing s o they suffered water stress at electrical conductivities higher than approximately 40 dS m-1 (equivalent to approximately - 1.4 MPa). Trees adjacent to the stream used stream water directly in summer, but may have used stream water directly in summer, but may have used stream wa ter from the soil profile in winter, after the stream had risen and re charged the soil water. E. camaldulensis appeared to be partially oppo rtunistic in the sources of water they used.