Water storage in the wood and xylem cavitation in 1-year-old twigs of Populus deltoides Bartr

The possible role of water expelled from cavitated xylem conduits in the rehydration of water-stressed leaves has been studied in one-year-old twigs of populus dettoides Bartr. Twigs were dehydrated in air. At desired values of leaf water potential (>|JI) (between near full turgor and-1-62 MPa), twigs were placed in black plastic bags for 1-2h. Leaf water content was measured every 3-5 min before bagging and every 10 min in the dark. Hydraulic conductivity and xylem cavitation were measured both in the open and in the dark. Cavitation was monitored as ultrasound acous-tic emissions (AE). A critical i{;i value of-0-96 MPa was found, at which AE increased significantly while the leaf water deficit decreased by gain of water. Since the twigs were no longer attached to roots, it was con-cluded that water expelled from cavitated xylem con-duits was transported to the leaves, thus contributing to their rehydration. Xylem cavitation is discussed in terms of a 'leaf water deficit buffer mechanism', under not very severe water stress conditions. Key-words: Populus deltoides] poplar; xylem cavitation; leaf rehydration