Ecology

Water-use efficiency

Irrigation

Biology

Ecosystem

Environmental science

New Phytologist

Summary The terrestrial carbon and water cycles are intimately linked: the carbon cycle is driven by photosynthesis, while the water balance is dominated by transpiration, and both fluxes are controlled by plant stomatal conductance. The ratio between these fluxes, the plant water‐use efficiency (WUE), is a useful indicator of vegetation function. WUE can be estimated using several techniques, including leaf gas exchange, stable isotope discrimination, and eddy covariance. Here we compare global compilations of data for each of these three techniques. We show that patterns of variation in WUE across plant functional types (PFTs) are not consistent among the three datasets. Key discrepancies include the following: leaf‐scale data indicate differences between needleleaf and broadleaf forests, but ecosystem‐scale data do not; leaf‐scale data indicate differences between C 3 and C 4 species, whereas at ecosystem scale there is a difference between C 3 and C 4 crops but not grasslands; and isotope‐based estimates ...

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