Heat-induced increases in xylem vulnerability: Experimental evidence and possible mechanisms

Heat exposure reduced xylem embolism resistance in seven Australian and European tree species, with 50% loss occurring at 0.73 MPa less negative water potential and 7.8 kPa h earlier.

• Why it matters: Hotter droughts are linked to rising tree mortality, but it is unclear whether heat can shift xylem vulnerability rather than leaving it fixed.
• What they did: The study used the Optical Vulnerability Technique and VPD-corrected drying times, testing elevated temperature (+15 and +20 degrees C above ambient) across seven species.
• The result: Heat-exposed plants showed reduced resistance and faster dehydration, consistent with a gas–bubble stability framework, implying embolism resistance may not be static and warranting mortality-focused heatwave tests.

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