Historical changes in the stomatal limitation of photosynthesis: empirical support for an optimality principle

Aliénor Lavergne*, Steve Voelker, Adam Csank, Heather Graven, Hugo J. de Boer, Valérie Daux, Iain Robertson, Isabel Dorado-Liñán, Elisabet Martínez-Sancho, Giovanna Battipaglia, Keith J. Bloomfield, Christopher J. Still, Frederick C. Meinzer, Todd E. Dawson, J. Julio Camarero, Rory Clisby, Yunting Fang, Annette Menzel, Rachel M. Keen, John S. RodenI. Colin Prentice

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


The ratio of leaf internal (ci) to ambient (ca) partial pressure of CO2, defined here as χ, is an index of adjustments in both leaf stomatal conductance and photosynthetic rate to environmental conditions. Measurements and proxies of this ratio can be used to constrain vegetation model uncertainties for predicting terrestrial carbon uptake and water use. 

We test a theory based on the least-cost optimality hypothesis for modelling historical changes in χ over the 1951–2014 period, across different tree species and environmental conditions, as reconstructed from stable carbon isotopic measurements across a global network of 103 absolutely dated tree-ring chronologies. The theory predicts optimal χ as a function of air temperature, vapour pressure deficit, ca and atmospheric pressure. 

The theoretical model predicts 39% of the variance in χ values across sites and years, but underestimates the intersite variability in the reconstructed χ trends, resulting in only 8% of the variance in χ trends across years explained by the model. 

Overall, our results support theoretical predictions that variations in χ are tightly regulated by the four environmental drivers. They also suggest that explicitly accounting for the effects of plant-available soil water and other site-specific characteristics might improve the predictions.

Original languageEnglish
Pages (from-to)2484-2497
Number of pages14
JournalNew Phytologist
Issue number6
Publication statusPublished - Mar 2020


  • leaf-internal CO concentration
  • least-cost hypothesis
  • optimality
  • stable carbon isotopes
  • tree rings
  • water-use efficiency


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