Abstract
Abstract Elevated atmospheric carbon dioxide (C a ) usually reduces stomatal conductance, but the effects on plant transpiration in the field are not well understood. Using constant‐power sap flow gauges, we measured transpiration from Quercus myrtifolia Willd., the dominant species of the Florida scrub‐oak ecosystem, which had been exposed in situ to elevated C a (350 µmol mol − 1 above ambient) in open‐top chambers since May 1996. Elevated C a reduced average transpiration per unit leaf area by 37%, 48% and 49% in March, May and October 2000, respectively. Temporarily reversing the C a treatments showed that at least part of the reduction in transpiration was an immediate, reversible response to elevated C a . However, there was also an apparent indirect effect of C a on transpiration: when transpiration in all plants was measured under common C a , transpiration in elevated C a ‐grown plants was lower than that in plants grown in normal ambient C a . Results from measurements of stomatal conductance (g s ), leaf area index (LAI), canopy light interception and correlation between light and g s indicated that the direct, reversible C a effect on transpiration was due to changes in g s caused by C a , and the indirect effect was caused mainly by greater self‐shading resulting from enhanced LAI, not from stomatal acclimation. By reducing light penetration through the canopy, the enhanced self‐shading at elevated C a decreased stomatal conductance and transpiration of leaves at the middle and bottom of canopy. This self‐shading mechanism is likely to be important in ecosystems where LAI increases in response to elevated C a .
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Claims 5
Claim · model-written summary
Elevated CO2 reduced March 2000 transpiration per unit leaf area by 37%
- Taxon
- Quercus myrtifolia
.jpg?width=60)
Quercus myrtifoliae0 - Treatment
- Elevated C ae1
- Outcome
- average transpiration per unit leaf areae1
- Direction
- reducede1
- Value
- 37%e1
- Qualifier
- Marche1
- Comparator
- ambiente2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
e0“we measured transpiration from Quercus myrtifolia Willd.”
e1“Elevated C a reduced average transpiration per unit leaf area by 37%, 48% and 49% in March, May and October 2000, respectively”
e2“exposed in situ to elevated C a (350 µmol mol − 1 above ambient)”
Claim · model-written summary
Elevated CO2 reduced May 2000 transpiration per unit leaf area by 48%
- Taxon
- Quercus myrtifoliaQuercus myrtifoliae0
- Treatment
- Elevated C ae1
- Outcome
- average transpiration per unit leaf areae1
- Direction
- reducede1
- Value
- 48%e1
- Qualifier
- Maye1
- Comparator
- ambiente2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we measured transpiration from Quercus myrtifolia Willd.”
e1“Elevated C a reduced average transpiration per unit leaf area by 37%, 48% and 49% in March, May and October 2000, respectively”
e2“exposed in situ to elevated C a (350 µmol mol − 1 above ambient)”
Claim · model-written summary
Elevated CO2 reduced October 2000 transpiration per unit leaf area by 49%
- Taxon
- Quercus myrtifoliaQuercus myrtifoliae0
- Treatment
- Elevated C ae1
- Outcome
- average transpiration per unit leaf areae1
- Direction
- reducede1
- Value
- 49%e1
- Qualifier
- Octobere1
- Comparator
- ambiente2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we measured transpiration from Quercus myrtifolia Willd.”
e1“Elevated C a reduced average transpiration per unit leaf area by 37%, 48% and 49% in March, May and October 2000, respectively”
e2“exposed in situ to elevated C a (350 µmol mol − 1 above ambient)”
Claim · model-written summary
Part of the transpiration reduction under elevated CO2 is an immediate, reversible response
- Taxon
- Quercus myrtifoliaQuercus myrtifoliae0
- Outcome
- reduction in transpiratione3
- Qualifier
- immediate, reversible response to elevated C ae3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we measured transpiration from Quercus myrtifolia Willd.”
e3“Temporarily reversing the C a treatments showed that at least part of the reduction in transpiration was an immediate, reversible response to elevated C a”
Claim · model-written summary
An indirect effect of elevated CO2 on transpiration is caused mainly by greater self-shading
- Taxon
- Quercus myrtifoliaQuercus myrtifoliae0
- Outcome
- indirect effecte4
- Qualifier
- caused mainly by greater selfe5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we measured transpiration from Quercus myrtifolia Willd.”
e4“However, there was also an apparent indirect effect of C a on transpiration”
e5“the indirect effect was caused mainly by greater self”