Abstract
Soybeans were grown for three seasons in open-top field chambers to determine (1) whether elevated CO2 (360 versus 700 μmol mol−1) alleviates some of the yield loss due to pollutant O3, (2) whether the partial stomatal closure resulting from chronic O3 exposure (charcoal-filtered air versus 1.5 × ambient concentrations) is a cause or result of decreased photosynthesis, and (3) possible implications of CO2/O3 interactions to climate change studies using elevated CO2. Leaf conductance was reduced by elevated CO2, regardless of O3 level, or by exposure to O3 alone. As.a result of these effects on conductance, high CO2 reduced estimated midday O3 flux into the leaf by an average of 50% in charcoal-filtered air and 35% in the high O3 treatment. However, while exposure to O3 reduced seed yields by 41% at ambient CO2 levels, the yield reduction was completely ameliorated by elevated CO2. The threshold midday O3 flux for yield loss appears to be 20–30 nmol m−2 s−1 in this study. Although elevated CO2 increased total biomass production, it did not increase seed yields. A/Ci curves show a large reduction in the stomatal limitation to photosynthesis due to elevated CO2 but no effect of O3. These data demonstrate that (1) reduced conductance due to O3 is the result, and not the cause, of reduced photosynthesis, (2) 700 μmol mol−1 CO2 can completely ameliorate yield losses due to O3 within the limits of these experiments, and (3) some reports of increased yields under elevated CO2 treatments may, at least in part, reflect the amelioration of unrecognized suppression of yield by O3 or other stresses.
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Claims 13
Claim · model-written summary
Elevated CO2 reduced leaf conductance regardless of O3 level.
- Taxon
- Soybeans
Glycine maxe0 - Treatment
- elevated CO2e1
- Outcome
- Leaf conductancee1
- Direction
- reducede1
- Qualifier
- regardless of O3 levele1
- Setting
- open-top field chamberse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e1“Leaf conductance was reduced by elevated CO2, regardless of O3 level, or by exposure to O3 alone”
Claim · model-written summary
Exposure to O3 alone reduced leaf conductance relative to charcoal-filtered air.
- Taxon
- SoybeansGlycine maxe0
- Treatment
- exposure to O3 alonee1
- Outcome
- Leaf conductancee1
- Direction
- reducede1
- Comparator
- charcoal-filtered aire2
- Setting
- open-top field chamberse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e1“Leaf conductance was reduced by elevated CO2, regardless of O3 level, or by exposure to O3 alone”
e2“charcoal-filtered air versus 1.5 × ambient concentrations”
Claim · model-written summary
High CO2 reduced estimated midday O3 flux into the leaf by 50% in charcoal-filtered air.
- Taxon
- SoybeansGlycine maxe0
- Treatment
- high CO2e3
- Outcome
- estimated midday O3 flux into the leafe3
- Direction
- reducede3
- Value
- 50%e3
- Qualifier
- in charcoal-filtered aire3
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e3“high CO2 reduced estimated midday O3 flux into the leaf by an average of 50% in charcoal-filtered air and 35% in the high O3 treatment”
Claim · model-written summary
High CO2 reduced estimated midday O3 flux into the leaf by 35% in the high O3 treatment.
- Taxon
- SoybeansGlycine maxe0
- Treatment
- high CO2e3
- Outcome
- estimated midday O3 flux into the leafe3
- Direction
- reducede3
- Value
- 35%e3
- Qualifier
- in the high O3 treatmente3
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e3“high CO2 reduced estimated midday O3 flux into the leaf by an average of 50% in charcoal-filtered air and 35% in the high O3 treatment”
Claim · model-written summary
Exposure to O3 reduced seed yield by 41% at ambient CO2 levels.
- Taxon
- SoybeansGlycine maxe0
- Treatment
- exposure to O3e4
- Outcome
- seed yieldse4
- Direction
- reducede4
- Value
- 41%e4
- Qualifier
- at ambient CO2 levelse4
- Comparator
- charcoal-filtered aire2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e2“charcoal-filtered air versus 1.5 × ambient concentrations”
e4“exposure to O3 reduced seed yields by 41% at ambient CO2 levels, the yield reduction was completely ameliorated by elevated CO2”
Claim · model-written summary
Elevated CO2 completely ameliorated the O3-induced reduction in seed yield.
- Taxon
- SoybeansGlycine maxe0
- Treatment
- elevated CO2e4
- Outcome
- yield reductione4
- Direction
- completely amelioratede4
- Comparator
- exposure to O3e4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e4“exposure to O3 reduced seed yields by 41% at ambient CO2 levels, the yield reduction was completely ameliorated by elevated CO2”
Claim · model-written summary
The threshold midday O3 flux for yield loss appears to be 20–30 nmol m−2 s−1.
- Taxon
- SoybeansGlycine maxe0
- Outcome
- threshold midday O3 flux for yield losse5
- Value
- 20–30 nmol m−2 s−1e5
- Qualifier
- appears to bee5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e5“The threshold midday O3 flux for yield loss appears to be 20–30 nmol m−2 s−1 in this study”
Claim · model-written summary
Elevated CO2 increased total biomass production.
- Taxon
- SoybeansGlycine maxe0
- Treatment
- elevated CO2e6
- Outcome
- total biomass productione6
- Direction
- increasede6
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e6“Although elevated CO2 increased total biomass production, it did not increase seed yields”
Claim · model-written summary
Elevated CO2 did not increase seed yields.
- Taxon
- SoybeansGlycine maxe0
- Treatment
- elevated CO2e6
- Outcome
- seed yieldse6
- Direction
- did not increasee6
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e6“Although elevated CO2 increased total biomass production, it did not increase seed yields”
Claim · model-written summary
Elevated CO2 showed a large reduction in the stomatal limitation to photosynthesis.
- Taxon
- SoybeansGlycine maxe0
- Treatment
- elevated CO2e7
- Outcome
- stomatal limitation to photosynthesise7
- Direction
- reductione7
- Qualifier
- largee7
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e7“A/Ci curves show a large reduction in the stomatal limitation to photosynthesis due to elevated CO2 but no effect of O3”
Claim · model-written summary
O3 had no effect on the stomatal limitation to photosynthesis in A/Ci curves.
- Taxon
- SoybeansGlycine maxe0
- Treatment
- O3e7
- Outcome
- stomatal limitation to photosynthesise7
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e7“A/Ci curves show a large reduction in the stomatal limitation to photosynthesis due to elevated CO2 but no effect of O3”
Claim · model-written summary
Reduced conductance due to O3 is the result, and not the cause, of reduced photosynthesis.
- Taxon
- SoybeansGlycine maxe0
- Treatment
- O3e2
- Outcome
- reduced photosynthesise2
- Qualifier
- reduced conductance due to O3 is the result, and not the cause, of reduced photosynthesise2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e2“reduced conductance due to O3 is the result, and not the cause, of reduced photosynthesis”
Claim · model-written summary
Some reports of increased yields under elevated CO2 may partly reflect amelioration of unrecognized yield suppression by O3 or other stresses.
- Taxon
- SoybeansGlycine maxe0
- Outcome
- increased yields under elevated CO2 treatmentse3
- Qualifier
- may, at least in part, reflect the amelioration of unrecognized suppression of yield by O3 or other stressese3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans were grown for three seasons in open-top field chambers”
e3“some reports of increased yields under elevated CO2 treatments may, at least in part, reflect the amelioration of unrecognized suppression of yield by O3 or other stresses”
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