A simple stomatal model that unifies the metabolic and hydraulic control of carbon and water flux

Authors: BUCKLEY, THOMAS - Uc Davis Arboretum And Public Garden; LAMOUR, JULIEN - University Of Toulouse; Barnard, David; BUCKLEY, DANIEL - Uc Davis Arboretum And Public Garden; JARVIS, ANDREW - Lancaster University; DIAZ-ESPEJO, ANTONIO - Instituto De Recursos Naturales Y Agrobiologia De Sevilla (IRNAS-CSIC); ROGERS, ALISTAIR - Lawrence Berkeley National Laboratory; SACK, LAWREN - University Of California (UCLA)

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2026
Publication Date: 7/11/2026
Citation: Buckley, T.N., Lamour, J., Barnard, D.M., Buckley, D.W., Jarvis, A.J., Diaz-Espejo, A., Rogers, A., Sack, L. 2026. A simple stomatal model that unifies the metabolic and hydraulic control of carbon and water flux. Global Change Biology. 32(7). Article e70999. https://doi.org/10.1111/gcb.70999.
DOI: https://doi.org/10.1111/gcb.70999

Interpretive Summary: A long-standing mismatch exists in the way land-surface models predict how vegetation interacts with the atmosphere through stomata, small pores in the leaves that balance carbon dioxide (CO2) uptake for photosynthesis with water loss. At large scales, photosyntheses is estimated using detailed biochemical models, whereas stomatal behavior relies on empirical models that do not fully capture mechanisms such as drought responses. This inconsistency reduces confidence in model predictions, especially under new or extreme environmental conditions. This study presents a new process-based stomatal conductance model that addresses this mismatch while remaining simple enough for use in large-scale land surface models. With only four parameters, the model overcomes key limitations of current approaches. This new model can predict how stomata respond to soil and atmospheric drought, account for the role of plant water transport, simulate stomatal behavior in the dark under dry conditions, explain opening at high temperatures when humidity stays constant, and reflect natural differences in photosynthetic capacity. Because the model is grounded in physiological mechanisms, its predictions can be connected across scales ranging from molecular processes within leaves to global patterns of ecosystem and land-surface function, and applied with greater confidence to future environmental scenarios.

Technical Abstract: A striking incongruity has long persisted in the modeling framework used to predict CO2 and water vapor exchange between land plants and the atmosphere. At large scales, photosynthetic CO2 demand is predicted using biochemical models, but the stomatal constraint on photosynthesis and transpiration is predicted using empirical models. This greatly limits confidence in predictions made outside the narrow domain in which those empirical models can be parameterized. We present a novel process-based model that can resolve this incongruity, while still being tractable enough for application in large scale land-surface models (LSMs), and having only four parameters. The model overcomes key limitations of the empirical models currently used by most LSMs, including predicting stomatal responses to soil drought, the influence of plant hydraulic conductance, stomatal closure in response to soil and atmospheric drought in darkness, stomatal opening at high temperatures when evaporative demand is held constant, and effects of natural and artificial variation in photosynthetic capacity, and can reproduce observed diurnal patterns of stomatal conductance in diverse species. Because all of the model's parameters, and its structure, are based on growing physiological knowledge, its predictions can be linked across scales – both down, towards underlying biophysical and molecular genetic causes, and up, towards ecosystem and global scales – and applied to future environmental conditions with greater confidence than possible within the current empirical paradigm.