Hydraulically-vulnerable trees survive on deep-water access during droughts in a tropical forest

Area of Science:

• Plant physiology
• Ecology
• Forest science

Background:

• Deep-water access is a critical, yet understudied, plant survival mechanism during drought.
• Hydraulic safety margins and embolism vulnerability predict mortality but may not fully account for delayed dehydration.
• Understanding root water uptake is key to predicting forest resilience in changing climates.

Purpose of the Study:

• To investigate the role of deep-water access in enabling plant survival within a diverse tropical forest.
• To quantify the relationship between effective rooting depth (ERD) and tree mortality during drought.
• To assess how ERD influences hydraulic traits and water stress compensation in canopy species.

Main Methods:

• Estimated effective rooting depth (ERD) for 29 canopy species using diameter growth data (1990-2015).
• Linked growth dynamics to environmental variables (vapor pressure deficit) and plant hydraulic traits (vulnerability curves).
• Validated ERD estimates using isotopic data of water-access depths.

Main Results:

• Deeper ERD was associated with higher maximum stem hydraulic conductivity and greater vulnerability to xylem embolism.
• Species with deeper ERD exhibited narrower hydraulic safety margins but lower mortality rates during extreme droughts.
• Increased ERD significantly reduced tree exposure to water stress, indicating compensation for drought risk.

Conclusions:

• Deep-water access is a crucial strategy for mitigating drought-induced mortality, especially for hydraulically vulnerable species.
• ERD is a key factor in forest resilience, enabling trees to compensate for water stress.
• Findings have significant implications for predicting tropical forest dynamics under future climate scenarios.