Extreme aridity pushes trees to their physical limits

Drought-induced hydraulic failure is a leading cause of mortality of trees (McDowell et al., 2008; Anderegg et al., 2012) and has become a major concern in light of future climate predictions, with forests across the world showing signs of vulnerability to intense and prolonged drought events (Allen et al., 2010). We show here that Callitris tuberculata, a conifer species from extremely dry areas of Western Australia, is the most cavitation resistant tree species in the world to date (mean xylem pressure leading to 50% loss of hydraulic function [P50] = 218.8 MPa). Hydraulic conductance is maintained in these plants at pressures remarkably close to the practical limit of water metastability, suggesting that liquid water transport under the cohesion-tension theory has reached its operational boundary.