Abstract
The mechanisms by which woody plants recover xylem hydraulic capacity
after drought stress are not well understood, particularly with regard
to the role of embolism refilling. We evaluated the recovery of xylem
hydraulic capacity in young Eucalyptus saligna plants exposed to
cycles of drought stress and rewatering. Plants were exposed to moderate
and severe drought stress treatments, with recovery monitored at time
intervals from 24 hrs to 6 months after rewatering. The percentage loss
of xylem vessels due to embolism (PLV) was quantified at each time point
using micro-computed tomography with stem water potential (Ψx) and whole
plant transpiration (Eplant) measured prior to scans. Plants exposed to
severe drought stress suffered high levels of embolism (47.38 ± 10.97 %
PLV) and almost complete canopy loss. No evidence of embolism refilling
was observed at 24 hrs, one week, or three weeks after rewatering
despite rapid recovery in Ψx. Recovery of hydraulic capacity was
achieved over a 6-month period by growth of new xylem tissue, with
canopy leaf area and Eplant recovering over the same period. These
findings indicate that E. saligna recovers slowly from severe
drought stress, with potential for embolism to persist in the xylem for
many months after rainfall.