Shoot desiccation and hydraulic failure in temperate woody angiosperms during an extreme summer drought

Plant water status and hydraulics were measured in six woody angiosperms growing in a karstic woodland, during an extreme summer drought. Our aim was to take advantage of an unusual climatic event to identify key traits related to species-specific mortality risk. The damage suffered by different species was assessed in terms of percentage of desiccated individuals. Stem water potential (Ystem) and loss of hydraulic conductivity (PLC) were measured in healthy and desiccated individuals. Vulnerability to cavitation was assessed in terms of stem water potential inducing 50% PLC (Y50). Wood density (WD) was also measured. Species-specific percentage of desiccated individuals was correlated to Y50 and WD. Crown desiccation was more widespread in species with less negative Y50 and lower WD. Desiccated individuals had lower Ystem and higher PLC than healthy ones, suggesting that hydraulic failure was an important mechanism driving shoot dieback. Drought-vulnerable species showed lower safety margins (Ystem - Y50) than resistant ones. Y50, safety margins and WD emerge as convenient traits to be used for tentative predictions of differential species-specific impact of extreme drought events on a local scale. The possibility that carbohydrate depletion was also involved in induction of desiccation symptoms is discussed.