ROOT-GROWTH, WATER-UPTAKE AND CANOPY DEVELOPMENT IN EUCALYPTUS-VIMINALIS SEEDLINGS

A split-root experiment was conducted using Eucalyptus viminalis seedl ings which were exposed to three watering regimes in order to investig ate root growth and soil water extraction under conditions of a drying soil profile. Seedlings were grown in columns in which the soil was d ivided horizontally with a soft wax plate. Watering treatments were co mposed of (1) both upper and lower sections of the column well watered (W/W), (2) only the lower section well watered (D/W), and (3) water w ithheld completely from both upper and lower sections (D/D). Daily mea surements included soil water potential (Psi(s)), column water loss an d leaf elongation. Increase in above- and below-ground biomass was det ermined from initial and final harvests after 25 days of treatment. Wh ole-column water loss and leaf extension were-depressed as Psi(s), in the upper section of D/W and D/D decreased to -0.4 MPa over the first 8-10 days. However, water loss did not decrease significantly in the l ower section of treatment D/W relative to the lower section of treatme nt W/W during this period. This indicated that water extraction by roo ts remaining in wet soil was not severely inhibited by the decrease in transpiration associated with the soil conditions in the upper profil e. Root distribution at the end of the experiment indicated significan t growth in the lower section of treatment D/W. There was evidence tha t hydraulic lifting of water between column sections may have occurred , as periodic increases in soil water potential of the unwatered upper section of D/W were observed.