Abstract:
The response of three Eucalyptus spp. clones (GC550, GU2IO and TAG 14) to soil moisture condition was assessed by means of plant water status, leaf gas exchange and stem xylem vulnerability. Data for 14 months old grown in 25 I pots clones were collected on the diurnal variation in leaf water potential (if/J, stomatal conductance (gj and net CO, assimilation rate (A). Main stem xylem vulnerability was assessed using ultrasonic acoustic emissions (LJAE). Vulnerability of the main stem was assessed as the leaf water potential corresponding to the maximum rate of acoustic emissions (y/,, EPHniar), and as the critical water potential triggering cavitation events, calculated as the mean of the water potentials of data points lying between 5 and 10% of the total accumulated emissions
(cUAE,%). Early stomatal closure was apparent, maintaining l constant during the middle of the day in all clones. Stem xylem vulnerability, assessed as both y//,EPHimn and y/(.4l.cUAE,% showed that the main stem of GC550 was more vulnerable than other two clones, and that low watered plants were more resistant to xylem cavitation than those receiving high water. Midday y/f fell below the vulnerability values assessed by both measures across treatments and clones, suggesting lack of stomatal control preventing stem xylem cavitation.
