The DroughtBox: A new tool for phenotyping residual branch conductance and its temperature dependence during drought
Billon, Lise M. | Blackman, Chris J. | Cochard, Hervé | Badel, Eric | Hitmi, Adnane | Cartailler, Julien | Souchal, Romain | Torres‐Ruiz, José M.
Xylem hydraulic failure is a major driver of tree death during drought. However, to better understand mortality risk in trees, especially during hot‐drought events, more information is required on both rates of residual water‐loss from small branches (gᵣₑₛ) after stomatal closure, as well as the phase transition temperature (Tₚ), beyond which gᵣₑₛ significantly increases. Here, we describe and test a novel low‐cost tool, the DroughtBox, for phenotyping gᵣₑₛ and Tₚ across species. The system consists of a programmable climatically controlled chamber in which branches dehydrate and changes in the mass recorded. Test measurements show that the DroughtBox maintains stable temperature and relative humidity across a range of set points, a prerequisite for getting accurate gᵣₑₛ and Tₚ values. Among a study group of four conifer and one angiosperm species, we observed a range of gᵣₑₛ (0.44–1.64 mmol H₂O m⁻² s⁻¹) and Tₚ (39.4–43.8°C) values. Furthermore, the measured time to hydraulic failure varied between two conifers species and was shortened in both species following a heatwave event. The DroughtBox is a reliable and customizable tool for phenotyping gᵣₑₛ and Tₚ, as well as for testing models of time to hydraulic failure that will improve our ability to assess climate change impacts on plants.
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