Abstract
The carbon dioxide concentration in free air carbon dioxide enrichment (FACE) systems typically has rapid fluctuations. In our FACE system, power spectral analysis of CO2 concentration measured every second with an open path analyzer indicated peaks in variation with a period of about one minute. I used open-top chambers to expose cotton and wheat plants to either a constant elevated CO2 concentration of 180 μmol mol-1 above that of outside ambient air, or to the same mean CO2 concentration, but with the CO2 enrichment cycling between about 30 and 330 μmol mol-1 above the concentration of outside ambient air, with a period of one minute. Three short-term replicate plantings of cotton were grown in Beltsville, Maryland with these CO2 concentration treatments imposed for 27-day periods over two summers, and one winter wheat crop was grown from sowing to maturity. In cotton, leaf gas-exchange measurements of the continuously elevated treatment and the fluctuating treatment indicated that the fluctuating CO2 concentration treatment consistently resulted in substantial down-regulation of net photosynthetic rate (P N) and stomatal conductance (g s). Total shoot biomass of the vegetative cotton plants in the fluctuating CO2 concentration treatment averaged 30% less than in the constantly elevated CO2 concentration treatment at 27 days after planting. In winter wheat, leaf gas-exchange measurements also indicated that down-regulation of P N and g s occurred in flag leaves in the fluctuating CO2 concentration treatment, but the effect was not as consistent in other leaves, nor as severe as found in cotton. However, wheat grain yields were 12% less in the fluctuating CO2 concentration treatment compared with the constant elevated CO2 concentration treatment. Comparison with wheat yields in chambers without CO2 addition indicated a nonsignificant increase of 5% for the fluctuating elevated CO2 concentration treatment, and a significant increase of 19% for the constant elevated treatment. The results suggest that treatments with fluctuating elevated CO2 concentrations could underestimate plant growth at projected future atmospheric CO2 concentrations.
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Claims 8
Claim · model-written summary
In the FACE system, CO2 concentration varied with peaks about one minute apart.
- Taxon
- cotton and wheat
Gossypium hirsutum
Triticum aestivumt0 - Outcome
- peaks in variatione0
- Value
- about one minutee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“power spectral analysis of CO2 concentration measured every second with an open path analyzer indicated peaks in variation with a period of about one minute.”
t0“cotton and wheat”
Claim · model-written summary
Fluctuating CO2 down-regulated cotton net photosynthetic rate and stomatal conductance relative to continuous elevation.
- Taxon
- cottonGossypium hirsutume0
- Organ / stage
- leafe0
- Treatment
- fluctuating CO2 concentration treatmente0
- Outcome
- net photosynthetic rate (P N) and stomatal conductance (g s)e0
- Direction
- down-regulatione0
- Comparator
- continuously elevated treatmente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In cotton, leaf gas-exchange measurements of the continuously elevated treatment and the fluctuating treatment indicated that the fluctuating CO2 concentration treatment consistently resulted in substantial down-regulation of net photosynthetic rate (P N) and stomatal conductance (g s).”
Claim · model-written summary
Fluctuating CO2 reduced cotton shoot biomass by 30% at 27 days.
- Taxon
- cottonGossypium hirsutume0
- Treatment
- fluctuating CO2 concentration treatmente0
- Outcome
- Total shoot biomasse0
- Direction
- lesse0
- Value
- 30%e0
- Qualifier
- at 27 days after plantinge0
- Comparator
- constantly elevated CO2 concentration treatmente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Total shoot biomass of the vegetative cotton plants in the fluctuating CO2 concentration treatment averaged 30% less than in the constantly elevated CO2 concentration treatment at 27 days after planting.”
Claim · model-written summary
Fluctuating CO2 down-regulated photosynthesis and stomatal conductance in wheat flag leaves.
- Taxon
- winter wheatTriticum aestivume0
- Organ / stage
- flag leavese0
- Treatment
- fluctuating CO2 concentration treatmente0
- Outcome
- P N and g se0
- Direction
- down-regulatione0
- Qualifier
- not as consistent in other leaves, nor as severe as found in cottone0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In winter wheat, leaf gas-exchange measurements also indicated that down-regulation of P N and g s occurred in flag leaves in the fluctuating CO2 concentration treatment, but the effect was not as consistent in other leaves, nor as severe as found in cotton.”
Claim · model-written summary
Wheat grain yield was 12% less with fluctuating than constant elevated CO2.
- Taxon
- wheatTriticum aestivume0
- Treatment
- fluctuating CO2 concentration treatmente0
- Outcome
- grain yieldse0
- Direction
- lesse0
- Value
- 12%e0
- Comparator
- constant elevated CO2 concentration treatmente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“wheat grain yields were 12% less in the fluctuating CO2 concentration treatment compared with the constant elevated CO2 concentration treatment.”
Claim · model-written summary
Wheat yield increased nonsignificantly by 5% with fluctuating elevated CO2 versus no addition.
- Taxon
- wheatTriticum aestivume0
- Treatment
- fluctuating elevated CO2 concentration treatmente0
- Outcome
- wheat yieldse0
- Direction
- increasee0
- Value
- 5%e0
- Comparator
- chambers without CO2 additione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Comparison with wheat yields in chambers without CO2 addition indicated a nonsignificant increase of 5% for the fluctuating elevated CO2 concentration treatment”
Claim · model-written summary
Wheat yield increased significantly by 19% with constant elevated CO2 versus no addition.
- Taxon
- wheatTriticum aestivume0
- Treatment
- constant elevated treatmente0
- Outcome
- wheat yieldse0
- Direction
- increasee0
- Value
- 19%e0
- Comparator
- chambers without CO2 additione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Comparison with wheat yields in chambers without CO2 addition indicated a nonsignificant increase of 5% for the fluctuating elevated CO2 concentration treatment, and a significant increase of 19% for the constant elevated treatment.”
Claim · model-written summary
Fluctuating elevated CO2 treatments could underestimate growth under future atmospheric CO2.
- Taxon
- cotton and wheatGossypium hirsutumTriticum aestivumt0
- Outcome
- plant growthe0
- Qualifier
- at projected future atmospheric CO2 concentrationse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The results suggest that treatments with fluctuating elevated CO2 concentrations could underestimate plant growth at projected future atmospheric CO2 concentrations.”
t0“cotton and wheat”
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See all 203 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.