Xylem embolism threshold for catastrophic hydraulic failure in angiosperm trees

Area of Science:

• Plant Physiology
• Ecology
• Forest Science

Background:

• Hydraulic failure is a primary driver of tree mortality during severe drought.
• While conifer cavitation resistance is linked to drought tolerance, angiosperm thresholds for xylem dysfunction are less understood.

Purpose of the Study:

• To investigate the relationship between drought tolerance, survival, and xylem cavitation resistance in five angiosperm tree species.
• To determine the embolism threshold for irreversible drought damage in angiosperms.

Main Methods:

• Seedlings were subjected to severe drought in a greenhouse to induce water stress.
• Leaf water potential, water loss, transpiration, stomatal conductance, and CO2 assimilation were monitored.
• Plant recovery after rewatering was used to identify critical water potential thresholds.
• Stem xylem cavitation resistance was assessed using vulnerability curves.

Main Results:

• A minimum recoverable water potential, consistent across ecophysiological variables, ranged from -3.4 to -6.0 MPa.
• This potential strongly correlated with P50 and P88 (pressures causing 50% and 88% hydraulic conductance loss).
• Irreversible drought damage in angiosperms occurred around 88% xylem embolism, differing from the 50% threshold in conifers.

Conclusions:

• Angiosperm trees exhibit hydraulic failure and irreversible drought damage at high embolism levels (around 88%).
• This threshold suggests distinct physiological adaptations in angiosperm stem water transport compared to conifers.
• Understanding these embolism thresholds is crucial for predicting angiosperm survival under drought stress.