Hakea drought resistance determined by climate factors rather than functional traits

With drought risk and frequency increasing globally due to climate change, an understanding of drought tolerance for a wide range of plant species is becoming crucial for conservation management. Xylem cavitation, wherein gas embolisms form in the vasculature leading to hydraulic failure, has been shown to be a useful proxy for drought tolerance.

The family Proteaceae presents an interesting study group for drought tolerance due to its evolutionary history; its origin is in the wet environment of Gondwana, but it has since successfully colonized the arid regions of Australia. Across its members, the family shows a wide variety of functional and life-history traits that allow it to survive in these habitats.

In a new article published in Annals of Botany, lead author Osazee O. Oyanoghago and colleagues examined the factors affecting xylem cavitation in Proteaceae species from the genus Hakea. Using 16 different species grown in a common garden, the researchers used a centrifuge to induce xylem cavitation and quantify the tension required to generate a 50% loss of conductivity (P₅₀). The P₅₀ values were compared to various functional traits as well as the species’ home environment and life history.

Stem P₅₀ values varied significantly among species, with the strongest correlation occurring with rainfall and aridity at the species’ origin. Other traits contributing to drought avoidance but not specifically cavitation resistance included a terete (needle-like) leaf form, and a higher sapwood to leaf area ratio. In fact, there was no significant relationship found between P₅₀ and functional traits such as wood density and specific leaf area.

The common garden-generated data indicates that P₅₀ is a genetically determined trait, which makes it a reliable measure for predicting species’ response to drought conditions. “Findings from this study will provide baseline data for the scientific basis for adaptive management for Hakea, including conservation of threatened and widespread species through translocations and assisted migration respectively,” write the authors.