Abstract
Spring wheat was grown from emergence to grain maturity in two partial pressures of CO 2 ( p CO 2 ): ambient air of nominally 37 Pa and air enriched with CO 2 to 55 Pa using a free‐air CO 2 enrichment (FACE) apparatus. This experiment was the first of its kind to be conducted within a cereal field without the modifications or disturbance of microclimate and rooting environment that accompanied previous studies. It provided a unique opportunity to examine the hypothesis that continuous exposure of wheat to elevated p CO 2 will lead to acclimatory loss of photosynthetic capacity. The diurnal courses of photosynthesis and conductance for upper canopy leaves were followed throughout the development of the crop and compared to model‐predicted rates of photosynthesis. The seasonal average of midday photosynthesis rates was 28% greater in plants exposed to elevated p CO 2 than in contols and the seasonal average of the daily integrals of photosynthesis was 21% greater in elevated p CO 2 than in ambient air. The mean conductance at midday was reduced by 36%. The observed enhancement of photosynthesis in elevated p CO 2 agreed closely with that predicted from a mechanistic biochemical model that assumed no acclimation of photosynthetic capacity. Measured values fell below predicted only in the flag leaves in the mid afternoon before the onset of grain‐filling and over the whole diurnal course at the end of grain‐filling. The loss of enhancement at this final stage was attributed to the earlier senescence of flag leaves in elevated p CO 2 . In contrast to some controlled‐environment and field‐enclosure studies, this field‐scale study of wheat using free‐air CO 2 enrichment found little evidence of acclimatory loss of photosynthetic capacity with growth in elevated p CO 2 and a significant and substantial increase in leaf photosynthesis throughout the life of the crop.
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Claims 8
Claim · model-written summary
Elevated CO2 raised seasonal midday photosynthesis by 28%.
- Taxon
- spring‐wheat
Triticum aestivumt0 - Treatment
- elevated p CO 2e0
- Outcome
- midday photosynthesis ratese0
- Direction
- greatere0
- Value
- 28%e0
- Comparator
- contolse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The seasonal average of midday photosynthesis rates was 28% greater in plants exposed to elevated p CO 2 than in contols”
t0“spring‐wheat”
Claim · model-written summary
Elevated CO2 raised daily photosynthesis integrals by 21%.
- Taxon
- spring‐wheatTriticum aestivumt0
- Treatment
- elevated p CO 2e0
- Outcome
- daily integrals of photosynthesise0
- Direction
- greatere0
- Value
- 21%e0
- Comparator
- ambient aire0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the seasonal average of the daily integrals of photosynthesis was 21% greater in elevated p CO 2 than in ambient air”
t0“spring‐wheat”
Claim · model-written summary
Midday leaf conductance fell by 36% under elevated CO2.
- Taxon
- spring‐wheatTriticum aestivumt0
- Treatment
- air enriched with CO 2 to 55 Pae1
- Outcome
- conductance at middaye0
- Direction
- reducede0
- Value
- 36%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The mean conductance at midday was reduced by 36%”
e1“air enriched with CO 2 to 55 Pa”
t0“spring‐wheat”
Claim · model-written summary
The observed photosynthesis enhancement agreed closely with a model assuming no capacity acclimation.
- Taxon
- spring‐wheatTriticum aestivumt0
- Outcome
- enhancement of photosynthesise0
- Direction
- agreed closelye0
- Comparator
- mechanistic biochemical modele0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The observed enhancement of photosynthesis in elevated p CO 2 agreed closely with that predicted from a mechanistic biochemical model that assumed no acclimation of photosynthetic capacity”
t0“spring‐wheat”
Claim · model-written summary
Measured photosynthesis fell below model prediction in flag leaves in midafternoon before grain filling.
- Taxon
- spring‐wheatTriticum aestivumt0
- Organ / stage
- flag leavese0
- Outcome
- Measured valuese0
- Direction
- fell belowe0
- Comparator
- predictede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Measured values fell below predicted only in the flag leaves in the mid afternoon before the onset of grain‐filling”
t0“spring‐wheat”
Claim · model-written summary
Measured photosynthesis fell below model prediction across the day at the end of grain filling.
- Taxon
- spring‐wheatTriticum aestivumt0
- Outcome
- Measured valuese1
- Direction
- fell belowe1
- Qualifier
- end of grain‐fillinge0
- Comparator
- predictede1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“over the whole diurnal course at the end of grain‐filling”
e1“Measured values fell below predicted only in the flag leaves”
t0“spring‐wheat”
Claim · model-written summary
Loss of late-stage photosynthesis enhancement was attributed to earlier flag-leaf senescence under elevated CO2.
- Taxon
- spring‐wheatTriticum aestivumt0
- Organ / stage
- flag leavese0
- Outcome
- loss of enhancemente0
- Qualifier
- earlier senescencee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The loss of enhancement at this final stage was attributed to the earlier senescence of flag leaves in elevated p CO 2”
t0“spring‐wheat”
Claim · model-written summary
The field study found little evidence for photosynthetic capacity acclimation under elevated CO2.
- Taxon
- spring‐wheatTriticum aestivumt0
- Outcome
- acclimatory loss of photosynthetic capacitye0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“found little evidence of acclimatory loss of photosynthetic capacity with growth in elevated p CO 2”
t0“spring‐wheat”
The same questions in other papers
co2 · physiology: photosynthesis · Triticum aestivum (wheat)Positive and negative results
68 papers in the same direction as this paper · 28 in the opposite direction
- no effect
- no effect
- no effect
93 papers more in this group
See all 97 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.