Water stress-induced xylem hydraulic failure is a causal factor of tree mortality in beech and poplar

Extreme water stress episodes induce tree mortality, but the physiological mechanisms causing tree death are still poorly understood. This study tests the hypothesis that a potted trees ability to survive extreme monotonic water stress is determined by the cavitation resistance of its xylem tissue. Two species were selected with contrasting cavitation resistance (beech and poplar), and potted juvenile trees were exposed to a range of water stresses, causing up to 100 plant death. The lethal dose of water stress, defined as the xylem pressure inducing 50 mortality, differed sharply across species (175 and 45 MPa in poplar and beech, respectively). However, the relationships between tree mortality and the degree of cavitation in the stems were similar, with mortality occurring suddenly when 90 cavitation had occurred. Overall, the results suggest that cavitation resistance is a causal factor of tree mortality under extreme drought conditions.