EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

One stomatal model to rule them all? Evaluating competing hypotheses to regulate the exchange of carbon and water against experimental data

Manon Sabot1, Martin De Kauwe1, Belinda Medlyn2, and Andy Pitman1
Manon Sabot et al.
  • 1Climate Change Research Centre and ARC Centre of Excellence for Climate Extremes, University of New South Wales, Sydney NSW, Australia
  • 2Hawkesbury Institute for the Environment, Western Sydney University, Penrith NSW, Australia

Nearly 2/3 of the annual global evapotranspiration (ET) over land arises from the vegetation. Yet, coupled-climate models only attribute between 22% – 58% of the annual terrestrial ET to plants. In coupled-climate models, the exchange of carbon and water between the terrestrial biosphere and the atmosphere is simulated by land-surface models (LSMs). Within those LSMs, stomatal conductance (gs) models allow plants to regulate their transpiration and carbon uptake, but most are empirically linked to climate, soil moisture availabilty, and CO2. Therefore, how and which gs schemes are implemented within LSMs is a key source of model uncertainty. This uncertainty has led to considerable investment in theory development in the recent years; multiple alternative hypotheses of optimal leaf-level regulation of gas exchange have been proposed as solutions to reduce existing model biases. However, a systematic inter-model evaluation is lacking (i.e. inter-model comparison within a single framework is needed to understand how different mechanistic assumptions across these new gs models affect plant behaviour). Here, we asked how, and under what conditions, nine novel optimal gs models differ from one another. The models were trained to match under average conditions before being subjected to: (i) a dry-down, (ii) high vapour pressure deficit, and (iii) elevated CO2. These experiments allowed us to identify the models’ specific responses and sensitivities. To further assess whether the models’ responses were realistic, we tested them against photosynthetic and hydraulic field data measured along mesic-xeric gradients in Europe and Australia. Finally, we evaluated model performance versus model complexity and the amount of information taken in by each model, which enables us to make recommendations regarding the use of stomatal conductance schemes in global climate models.

How to cite: Sabot, M., De Kauwe, M., Medlyn, B., and Pitman, A.: One stomatal model to rule them all? Evaluating competing hypotheses to regulate the exchange of carbon and water against experimental data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-678,, 2019

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