Abstract
Abstract The microclimate in facilities for studying effects of elevated CO 2 on crops differs from ambient conditions. Open‐top chambers (OTCs) increase temperature by 1–3 °C. If temperature and CO 2 interact in their effect on crops, this would limit the value of OTC experiments. Furthermore, interaction of CO 2 and temperature deserves study because increases in atmospheric CO 2 concentration are expected to cause global warming. This paper describes two experiments in which a recently developed cooling system for OTCs was used to analyse the effects of temperature on photosynthesis, growth and yield of spring wheat ( Triticum aestivum L., cv. Minaret). Two levels of CO 2 were used (350 and 700 ppm), and two levels of temperature, with cooled OTCs being 1.6–2.4 °C colder than noncooled OTCs. Photosynthetic rates were increased by elevated CO 2 , but no effect of temperature was found. Cross‐switching CO 2 concentrations as well as determination of A–C i curves showed that plant photosynthetic capacity after anthesis acclimated to elevated CO 2 . The acclimation may be related to the effects of CO 2 on tissue composition: elevated CO 2 decreased leaf nitrogen concentrations and increased sugar content. Calculations of the seasonal mean crop light‐use efficiency (LUE) were consistent with the photosynthesis data in that CO 2 increased LUE by 20% on average whereas temperature had no effect. Both elevating CO 2 and cooling increased grain yield, by an average of 11% and 23%, respectively. CO 2 and temperature stimulated yield via different mechanisms: CO 2 increased photosynthetic rate, but decreased crop light interception capacity (LAI), whereas cooling increased grain yield by increasing LAI and extending the growing season with 10 days. The effects of CO 2 and temperature were not additive: the CO 2 effect was about doubled in the noncooled open‐top chambers. In most cases, effects on yield were mediated through increased grain density rather than increased individual grain weights. The higher growth response to elevated CO 2 in noncooled vs. cooled OTCs shows that a cooling system may remove a bias towards overestimating crop growth response to CO 2 in open‐top chambers.
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Claims 15
Claim · model-written summary
Elevated CO2 increased photosynthetic rates of spring wheat.
- Taxon
- Triticum aestivum
Triticum aestivume0 - Material
- cv. Minarete0
- Treatment
- elevated CO 2e1
- Outcome
- Photosynthetic ratese1
- Direction
- increasede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e1“Photosynthetic rates were increased by elevated CO 2 , but no effect of temperature was found”
Claim · model-written summary
Cooling the open-top chambers had no effect on photosynthetic rates of spring wheat.
- Taxon
- Triticum aestivumTriticum aestivume0
- Treatment
- temperaturee1
- Outcome
- Photosynthetic ratese1
- Direction
- no_changeinferrede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e1“Photosynthetic rates were increased by elevated CO 2 , but no effect of temperature was found”
Claim · model-written summary
Photosynthetic capacity of spring wheat after anthesis acclimated to elevated CO2.
- Taxon
- Triticum aestivumTriticum aestivume0
- Treatment
- elevated CO 2e2
- Outcome
- plant photosynthetic capacity after anthesise2
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e2“plant photosynthetic capacity after anthesis acclimated to elevated CO 2”
Claim · model-written summary
Elevated CO2 decreased leaf nitrogen concentrations of spring wheat.
- Taxon
- Triticum aestivumTriticum aestivume0
- Treatment
- elevated CO 2e3
- Outcome
- leaf nitrogen concentrationse3
- Direction
- decreasede3
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e3“elevated CO 2 decreased leaf nitrogen concentrations and increased sugar content”
Claim · model-written summary
Elevated CO2 increased sugar content of spring wheat leaves.
- Taxon
- Triticum aestivumTriticum aestivume0
- Organ / stage
- leafe3
- Treatment
- elevated CO 2e3
- Outcome
- sugar contente3
- Direction
- increasede3
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e3“elevated CO 2 decreased leaf nitrogen concentrations and increased sugar content”
Claim · model-written summary
Elevated CO2 increased seasonal mean light-use efficiency of the crop by 20% on average.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e4“CO 2 increased LUE by 20% on average whereas temperature had no effect”
Claim · model-written summary
Temperature had no effect on light-use efficiency of spring wheat.
- Taxon
- Triticum aestivumTriticum aestivume0
- Treatment
- temperaturee4
- Outcome
- LUEe4
- Direction
- no_changeinferrede4
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e4“CO 2 increased LUE by 20% on average whereas temperature had no effect”
Claim · model-written summary
Elevated CO2 increased grain yield of spring wheat by an average of 11%.
- Taxon
- Triticum aestivumTriticum aestivume0
- Treatment
- elevating CO 2e5
- Outcome
- grain yielde5
- Direction
- increasede5
- Value
- 11%e5
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e5“Both elevating CO 2 and cooling increased grain yield, by an average of 11% and 23%, respectively”
Claim · model-written summary
Cooling the open-top chambers increased grain yield of spring wheat by an average of 23%.
- Taxon
- Triticum aestivumTriticum aestivume0
- Treatment
- coolinge5
- Outcome
- grain yielde5
- Direction
- increasede5
- Value
- 23%e5
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e5“Both elevating CO 2 and cooling increased grain yield, by an average of 11% and 23%, respectively”
Claim · model-written summary
Elevated CO2 decreased crop light interception capacity (LAI) of spring wheat.
- Taxon
- Triticum aestivumTriticum aestivume0
- Treatment
- CO 2e6
- Outcome
- crop light interception capacity (LAI)e6
- Direction
- decreasede6
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e6“CO 2 increased photosynthetic rate, but decreased crop light interception capacity (LAI)”
Claim · model-written summary
Cooling increased the leaf area index (LAI) of spring wheat.
- Taxon
- Triticum aestivumTriticum aestivume0
- Treatment
- coolinge7
- Outcome
- LAIe7
- Direction
- increaseinferrede7
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e7“cooling increased grain yield by increasing LAI and extending the growing season with 10 days”
Claim · model-written summary
Cooling extended the growing season of spring wheat by 10 days.
- Taxon
- Triticum aestivumTriticum aestivume0
- Treatment
- coolinge7
- Outcome
- growing seasone7
- Direction
- increaseinferrede7
- Value
- 10 dayse7
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e7“cooling increased grain yield by increasing LAI and extending the growing season with 10 days”
Claim · model-written summary
The effects of CO2 and temperature on spring wheat were not additive.
- Taxon
- Triticum aestivumTriticum aestivume0
- Outcome
- effects of CO 2 and temperaturee6
- Qualifier
- not additivee6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e6“The effects of CO 2 and temperature were not additive”
Claim · model-written summary
The CO2 effect on crop growth was about doubled in noncooled open-top chambers.
- Taxon
- Triticum aestivumTriticum aestivume0
- Treatment
- CO 2e5
- Outcome
- CO2 effecte5
- Value
- about doublede5
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e5“the CO 2 effect was about doubled”
Claim · model-written summary
Effects of CO2 and cooling on wheat yield were mostly mediated through increased grain density rather than individual grain weight.
- Taxon
- Triticum aestivumTriticum aestivume0
- Outcome
- grain densitye4
- Direction
- increasede4
- Qualifier
- rather than increased individual grain weightse4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spring wheat ( Triticum aestivum L., cv. Minaret)”
e4“In most cases, effects on yield were mediated through increased grain density rather than increased individual grain weights”
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