How do leaf and ecosystem measures of water-use efficiency compare?

Area of Science:

• Ecology
• Plant Physiology
• Biogeochemistry

Background:

• Terrestrial carbon and water cycles are interconnected, regulated by plant stomatal conductance.
• Plant water-use efficiency (WUE) integrates these cycles and serves as a key vegetation function indicator.

Purpose of the Study:

• To compare global datasets of WUE estimated by leaf gas exchange, stable isotope discrimination, and eddy covariance.
• To identify and quantify discrepancies in WUE measurements across different plant functional types (PFTs) and methodologies.

Main Methods:

• Global data compilation and comparative analysis of three primary WUE estimation techniques: leaf gas exchange, stable isotope discrimination, and eddy covariance.
• Assessment of WUE variations across diverse plant functional types (PFTs).

Main Results:

• Inconsistent patterns of WUE variation across PFTs were observed among the three datasets.
• Discrepancies noted in forest type comparisons (needleleaf vs. broadleaf) and C3/C4 species/crop distinctions between leaf- and ecosystem-scale data.
• Isotope-based WUE estimates were generally higher than gas exchange-based estimates for most PFTs.

Conclusions:

• Significant uncertainty exists in current WUE measurement methods.
• Discrepancies pose potential biases for parameterizing and validating ecosystem models.
• Further research is crucial to reconcile differing WUE measurement techniques and improve ecological understanding.