RESTORATION OF CATCHMENT WATER-BALANCE - RESPONSES OF CLONAL RIVER RED GUM (EUCALYPTUS-CAMALDULENSIS) TO WATERLOGGING

Effects of waterlogging were studied in the field and under glasshouse conditions on two clonal lines of Eucalyptus camaldulensis Dehnh (riv er red gum), which are used in the rehabilitation of damaged agricultu ral catchments in Western Australia. The plantation of 9-year-old tree s was in a position that covered a range of waterlogging and salinity conditions. Upslope the water table was deeper (0.65-1.5 m), whereas t he water table was closer to the ground surface downslope (0.45 m in w inter; 1.25 m in summer). Salinity was greater downslope and increased at the end of the dry summer, remaining high until diluted by the win ter rains. Trees of both clonal lines were smaller downslope and used less water over the year. Clone M80 used more water in winter; clone M 66 more in summer. In the field, the roots of clone M80 were evenly di stributed through the soil profile, while roots of clone M66 decreased with increasing depth. Production of new root terminals varied with s eason. Greatest production was in spring and early summer, with much l ower production over late autumn and winter. Only clone M66 produced n ew root terminals at depth (60-75 cm) during the drier months of late summer and early autumn. At this time, saline groundwater was the main source for water uptake. To explore clonal differences more closely, the effects of prolonged waterlogging were studied under glasshouse co nditions. Clone M80 grew similarly under freely drained and continuous ly waterlogged conditions for the experimental period (21 weeks). The response under continuously waterlogged conditions was achieved throug h adventitious root production. By contrast, growth of clone M66 was s uppressed under continuous waterlogging, a response associated with th e lack of adventitious root production. The results from field and gla sshouse studies suggest that clone M80 is more adapted to waterlogging by relatively fresh water than clone M66, but that clone M66 may use water of higher salinity than clone M80. Clone M80 would be better sui ted to higher positions in partially cleared catchments, where rainfal l provides relatively fresh soil water. Clone M66 is better suited to lower catchment positions due to its ability to utilize more saline gr oundwater. Restoration of the water balance of damaged agricultural ca tchments can be best managed by matching specialized genotypes with pa rticular catchment positions.