Maximum leaf conductance driven by CO₂ effects on stomatal size and density over geologic time

Stomatal pores are microscopic structures on the epidermis of leaves formed by 2 specialized guard cells that control the exchange of water vapor and CO₂ between plants and the atmosphere. Stomatal size (S) and density (D) determine maximum leaf diffusive (stomatal) conductance of CO₂ (gcmax) to sit...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2009-06, Vol.106 (25), p.10343-10347
Main Authors: Franks, Peter J, Beerling, David J
Format: Article
Language:English
Subjects:
Atmosphere
Atmospherics
Biological Evolution
Biological Sciences
Carbon dioxide
Carbon Dioxide - metabolism
dimensions
Ecophysiology
Evolution
Evolution, Planetary
Fossils
gas exchange
Geologic time scale
Guard cells
leaf conductance
Leaves
Models, Theoretical
paleobotany
Physical Sciences
plant morphology
Plant Stomata - metabolism
Plant Stomata - physiology
Plants
stomata
stomatal conductance
stomatal density
stomatal size
Time Factors
Water vapor
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Summary:Stomatal pores are microscopic structures on the epidermis of leaves formed by 2 specialized guard cells that control the exchange of water vapor and CO₂ between plants and the atmosphere. Stomatal size (S) and density (D) determine maximum leaf diffusive (stomatal) conductance of CO₂ (gcmax) to sites of assimilation. Although large variations in D observed in the fossil record have been correlated with atmospheric CO₂, the crucial significance of similarly large variations in S has been overlooked. Here, we use physical diffusion theory to explain why large changes in S necessarily accompanied the changes in D and atmospheric CO₂ over the last 400 million years. In particular, we show that high densities of small stomata are the only way to attain the highest gcmax values required to counter CO₂"starvation" at low atmospheric CO₂ concentrations. This explains cycles of increasing D and decreasing S evident in the fossil history of stomata under the CO₂ impoverished atmospheres of the Permo-Carboniferous and Cenozoic glaciations. The pattern was reversed under rising atmospheric CO₂ regimes. Selection for small S was crucial for attaining high gcmax under falling atmospheric CO₂ and, therefore, may represent a mechanism linking CO₂ and the increasing gas-exchange capacity of land plants over geologic time.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.0904209106