To grow, plants open their stomates to capture carbon dioxide, whilst simultaneously losing water through the process of transpiration.

Previous work has shown that observations of this carbon for water exchange at the leaf scale, are inconsistent with measurements at the ecosystem scale (> kilometres). This paper explores six possible mechanisms for these discrepancies and adds to the growing body of research focused on plant water-use efficiency – the key metric that links the carbon and water cycles in land models.

The carbon cycle is driven by photosynthesis, whilst the water balance is dominated by transpiration. Both fluxes are controlled by plant stomatal conductance.

The ratio between these fluxes, the plant water-use efficiency is a useful indicator of vegetation function.

This study explored the key sources of uncertainty when scaling leaf-level understanding of water-use efficiency to ecosystem scales. The results provide key insights into interpreting (ecosystem-scale) eddy-covariance derived water-use efficiency in an ecophysiological context.

  • Paper: Knauer J, Zaehle S, Medlyn BE, et al. Towards physiologically meaningful water-use efficiency estimates from eddy covariance data. Glob Change Biol. 2018;24:694–710.