Articles | Volume 21, issue 7
Hydrol. Earth Syst. Sci., 21, 3377–3400, 2017
Hydrol. Earth Syst. Sci., 21, 3377–3400, 2017

Technical note 07 Jul 2017

Technical note | 07 Jul 2017

Technical note: An experimental set-up to measure latent and sensible heat fluxes from (artificial) plant leaves

Stanislaus J. Schymanski, Daniel Breitenstein, and Dani Or Stanislaus J. Schymanski et al.
  • Department of Environmental Systems Science, ETH Zurich, 8092 Zurich, Switzerland

Abstract. Leaf transpiration and energy exchange are coupled processes that operate at small scales yet exert a significant influence on the terrestrial hydrological cycle and climate. Surprisingly, experimental capabilities required to quantify the energy–transpiration coupling at the leaf scale are lacking, challenging our ability to test basic questions of importance for resolving large-scale processes. The present study describes an experimental set-up for the simultaneous observation of transpiration rates and all leaf energy balance components under controlled conditions, using an insulated closed loop miniature wind tunnel and artificial leaves with pre-defined and constant diffusive conductance for water vapour. A range of tests documents the above capabilities of the experimental set-up and points to potential improvements. The tests reveal a conceptual flaw in the assumption that leaf temperature can be characterized by a single value, suggesting that even for thin, planar leaves, a temperature gradient between the irradiated and shaded or transpiring and non-transpiring leaf side can lead to bias when using observed leaf temperatures and fluxes to deduce effective conductances to sensible heat or water vapour transfer. However, comparison of experimental results with an explicit leaf energy balance model revealed only minor effects on simulated leaf energy exchange rates by the neglect of cross-sectional leaf temperature gradients, lending experimental support to our current understanding of leaf gas and energy exchange processes.

Short summary
Leaf transpiration and energy exchange are coupled processes at the small scale that have strong effects on the water cycle and climate at the large scale. In this technical note, we present a novel experimental set-up that enables detailed study of these coupled processes in the laboratory under controlled conditions. Results document the abilities of the experimental set-up to confirm or challenge our understanding of these processes.