Abstract
Stomatal density is known to respond to CO 2 levels during leaf development. Current interest in the increasing concentration of atmospheric CO 2 has stimulated much experimentation on the responses of plants to relatively short-term exposure in artificially high CO 2 levels. Attempts to extrapolate from short-term to long-term responses raise fundamental questions concerning evolutionary change in response to rising global CO 2 levels. We consider the improved water use efficiency observed under elevated CO 2 levels to be the main driving force of natural selection affecting the genotypic component controlling stomatal density. Whether a response is merely phenotypic or becomes incorporated into the genotype depends on two factors: (i) the time scale of exposure and (ii) the generation time of a species. Measurements of stomatal density on fossil leaves of Salix herbacea through a glacial cycle covering the last 140 000 years have shown a decrease in stomatal density in response to the rising CO 2 levels of this period. This accords with the shorter-term observations on leaves of trees seen in herbarium specimens where the stomatal density has decreased in response to the rising CO 2 levels of the last 200 years. The results indicate that natural selection over the 140000-year period may have favoured a similar response to that shown by trees phenotypically over the last 200 years. Since there is now some evidence for the genetic control of stomatal density, the role of natural selection affecting it must be considered when translating responses from short-term experiments to predict how stomatal density will be affected by long-term climatic and atmospheric change.
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Claims 5
Claim · model-written summary
Fossil Salix herbacea leaves showed lower stomatal density as CO2 rose over a glacial cycle covering 140,000 years.
- Taxon
- Salix herbacea
Salix herbaceae0 - Organ / stage
- leavese0
- Outcome
- stomatal densitye0
- Direction
- decreasee0
- Qualifier
- last 140 000 yearse0
Not reportedTreatmentSetting
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Measurements of stomatal density on fossil leaves of Salix herbacea through a glacial cycle covering the last 140 000 years have shown a decrease in stomatal density in response to the rising CO 2 levels of this period.”
Claim · model-written summary
Herbarium tree leaves showed declining stomatal density as CO2 rose over the last 200 years.
Verbatim
e0“leaves of trees seen in herbarium specimens where the stomatal density has decreased in response to the rising CO 2 levels of the last 200 years”
Claim · model-written summary
The authors interpret long-term selection as possibly favoring a response similar to the shorter-term phenotypic response in trees.
Verbatim
e0“natural selection over the 140000-year period may have favoured a similar response to that shown by trees phenotypically over the last 200 years”
Claim · model-written summary
The authors propose improved water use efficiency under elevated CO2 as the main selective force affecting genetic control of stomatal density.
Not reportedTaxon
Verbatim
e0“improved water use efficiency observed under elevated CO 2 levels to be the main driving force of natural selection affecting the genotypic component controlling stomatal density”
t0“stomatal density”
Claim · model-written summary
The authors recommend considering natural selection when extrapolating short-term stomatal responses to long-term climatic and atmospheric change.
- Outcome
- the role of natural selection affecting it must be considerede0
Not reportedTaxon
Verbatim
e0“the role of natural selection affecting it must be considered when translating responses from short-term experiments to predict how stomatal density will be affected by long-term climatic and atmospheric change”