Water Relations in Eucalyptus regnans nursery plants following root exposure after lifting

Water relations of Eucalyptus regnans seedlings during root exposure and associated desiccation were studied in three trials. In the first, changes in water potential and relative water content (RWC) of leaves and hydraulic resistance in the lower stem were recorded during exposure. In the two subsequent trials, different exposure conditions resulted in different rates of desiccation. After various exposure times, roots were soaked for 24 h in aerated distilled water under continuous light before measuring root and whole plant hydraulic resistance. Exposure for 5-8 h and accompanying short term leaf water stress to below -2 MPa resulted in significant increases in hydraulic resistance of stem, roots and whole plant. Although leaf water potentials at the longest exposure times in one trial fell below the probable turgor loss point, there was no apparent permanent leaf damage. In the two trials in which roots were soaked before hydraulic resistances were measured, there was a marked difference in the response of leaf water potential to soaking. Although hydraulic resistance increased with longer exposure in both trials, the results from one trial suggested a further increase during soaking. Differences between the two trials suggested differences between plants before treatment or the soaking treatment itself may also have influenced water relations after exposure. Results are discussed in terms of the practical implications, particularly effects of nursery management on the condition of trees at lifting and subsequent water relations of lifted seedlings during and after transplanting. Some aspects of regulation of water stress by E. regnans seedlings are also discussed.