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Keywords:

  • cavitation;
  • crown desiccation;
  • drought;
  • hydraulic failure;
  • safety margin;
  • stem density;
  • stem water potential;
  • tree mortality

Summary

  • 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 drought damage.
  • The damage suffered by different species was assessed in terms of percentage of individuals showing extensive crown desiccation. Stem water potential (Ψstem) and percent 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 (Ψ50). Stem density (ρstem) was also measured.
  • Species-specific percentage of desiccated individuals was correlated to Ψ50 and ρstem. Crown desiccation was more widespread in species with less negative Ψ50 and lower ρstem. Desiccated individuals had lower Ψstem and higher PLC than healthy ones, suggesting that hydraulic failure was an important mechanism driving shoot dieback. Drought-vulnerable species showed lower safety margins (Ψstem − Ψ50) than resistant ones.
  • The Ψ50, safety margins and ρstem values 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.