Climate and functional traits jointly mediate tree water-use strategies

Area of Science:

• Plant physiology
• Ecology
• Hydrology

Background:

• Tree water use is crucial for plant function and ecosystem processes.
• Understanding how organ-level water relations coordinate whole-tree water use under drought is essential.
• The influence of climate on these coordination strategies remains unclear.

Purpose of the Study:

• To investigate the coordination of water-relations traits in determining whole-tree water-use strategies.
• To assess the impact of climate, specifically mean annual precipitation (MAP), on these strategies.
• To analyze the response of canopy conductance (G) to vapor pressure deficit (VPD) and soil water content (SWC) across 142 tree species.

Main Methods:

• Utilized the global sap flow database (SAPFLUXNET).
• Examined six key water-relations traits: embolism vulnerability, Huber value, hydraulic conductivity, turgor-loss point, rooting depth, and leaf size.
• Accounted for tree height and climate variables (MAP) in the analysis.

Main Results:

• Reference canopy conductance (G) and its sensitivity to VPD were strongly coordinated with water-relations traits, independent of MAP.
• Species with efficient xylem transport exhibited higher canopy conductance but also increased sensitivity to VPD.
• Angiosperms demonstrated higher reference G and VPD sensitivity compared to gymnosperms.

Conclusions:

• Water-relations traits, not climate, primarily dictate tree water-use strategies and drought responses.
• Trait integration is vital for understanding complex whole-plant water use.
• Defining a singular 'acquisitive' to 'conservative' resource-use spectrum for plants is challenging due to trait coordination complexities.