Abstract
The initial stimulation of photosynthesis observed on elevation of [CO2] in grasslands has been predicted to be a transient phenomenon constrained by the loss of photosynthetic capacity due to other limitations, notably nutrients and sinks for carbohydrates. Legumes might be expected partially to escape these feedbacks through symbiotic N2 fixation. The Free-Air Carbon dioxide Enrichment (FACE) experiment at Eschikon, Switzerland, has been the longest running investigation of the effects of open-air elevation of [CO2] on vegetation. The prediction of a long-term loss of photosynthetic capacity was tested by analysing photosynthesis in Trifolium repens L. (cv. Milkanova) in the spring and autumn of the eighth, ninth and tenth years of treatment. A high and low N treatment also allowed a test of the significance of exogenous N-supply in maintaining a stimulation of photosynthetic capacity in the long-term. Prior work in this Free Air CO2 Enrichment (FACE) experiment has revealed that elevated [CO2] increased both vegetative and reproductive growth of T. repens independent of N treatment. It is shown here that the photosynthetic response of T. repens was also independent of N fertilization under both current ambient and elevated (600 micro mol mol-1) [CO2]. There was a strong effect of season on photosynthesis, with light-saturated rates (Asat) 37% higher in spring than in autumn. Higher Asat in the spring was supported by higher maximum Rubisco carboxylation rates (Vc,max) and maximum rates of electron transport (Jmax) contributing to RuBP regeneration. Elevated [CO2] increased Asat by 37% when averaged across all measurement periods and both N fertilization levels, and decreased stomatal conductance by 25%. In spring, there was no effect of elevated [CO2] on photosynthetic capacity of leaves, but in autumn both Vc,max and Jmax were reduced by approximately 20% in elevated [CO2]. The results show that acclimation of photosynthetic capacity can occur in a nitrogen-fixing species, in the field where there are no artificial restrictions on sink capacity. However, even with acclimation there was a highly significant increase in photosynthesis at elevated [CO2].
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Claims 10
Claim · model-written summary
Photosynthetic response was independent of nitrogen fertilization under ambient and elevated carbon dioxide.
- Taxon
- T. repens
Trifolium repense0 - Treatment
- N fertilizatione0
- Outcome
- photosynthetic responsee0
- Direction
- independente0
- Qualifier
- current ambient and elevated (600 micro mol mol-1) [CO2]e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the photosynthetic response of T. repens was also independent of N fertilization under both current ambient and elevated (600 micro mol mol-1) [CO2].”
Claim · model-written summary
Light-saturated photosynthesis was 37% higher in spring than autumn.
- Taxon
- T. repensTrifolium repense0e1
- Outcome
- light-saturated rates (Asat)e0
- Direction
- highere0
- Value
- 37%e0
- Qualifier
- springe0
- Comparator
- autumne0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“light-saturated rates (Asat) 37% higher in spring than in autumn.”
e1“the photosynthetic response of T. repens”
Claim · model-written summary
Spring maximum Rubisco carboxylation rates were higher.
- Taxon
- T. repensTrifolium repense0e1
- Outcome
- maximum Rubisco carboxylation rates (Vc,max)e0
- Direction
- highere0
- Qualifier
- springe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Higher Asat in the spring was supported by higher maximum Rubisco carboxylation rates (Vc,max) and maximum rates of electron transport (Jmax) contributing to RuBP regeneration.”
e1“the photosynthetic response of T. repens”
Claim · model-written summary
Spring maximum electron transport rates were higher.
- Taxon
- T. repensTrifolium repense0e1
- Outcome
- maximum rates of electron transport (Jmax)e0
- Direction
- Highere0
- Qualifier
- springe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Higher Asat in the spring was supported by higher maximum Rubisco carboxylation rates (Vc,max) and maximum rates of electron transport (Jmax) contributing to RuBP regeneration.”
e1“the photosynthetic response of T. repens”
Claim · model-written summary
Elevated carbon dioxide increased light-saturated photosynthesis by 37%.
- Taxon
- T. repensTrifolium repense0e1
- Treatment
- Elevated [CO2]e0
- Outcome
- Asate0
- Direction
- increasede0
- Value
- 37%e0
- Qualifier
- averaged across all measurement periods and both N fertilization levelse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Elevated [CO2] increased Asat by 37% when averaged across all measurement periods and both N fertilization levels, and decreased stomatal conductance by 25%.”
e1“the photosynthetic response of T. repens”
Claim · model-written summary
Elevated carbon dioxide decreased stomatal conductance by 25%.
- Taxon
- T. repensTrifolium repense0e1
- Treatment
- Elevated [CO2]e0
- Outcome
- stomatal conductancee0
- Direction
- decreasede0
- Value
- 25%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Elevated [CO2] increased Asat by 37% when averaged across all measurement periods and both N fertilization levels, and decreased stomatal conductance by 25%.”
e1“the photosynthetic response of T. repens”
Claim · model-written summary
Elevated carbon dioxide had no effect on spring photosynthetic capacity of leaves.
- Taxon
- T. repensTrifolium repense0e1
- Treatment
- elevated [CO2]e0
- Outcome
- photosynthetic capacity of leavese0
- Direction
- no effecte0
- Qualifier
- springe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In spring, there was no effect of elevated [CO2] on photosynthetic capacity of leaves, but in autumn both Vc,max and Jmax were reduced by approximately 20% in elevated [CO2].”
e1“the photosynthetic response of T. repens”
Claim · model-written summary
Autumn Vc,max fell by approximately 20% under elevated carbon dioxide.
- Taxon
- T. repensTrifolium repense0e1
- Treatment
- elevated [CO2]e0
- Outcome
- Vc,maxe0
- Direction
- reducede0
- Value
- approximately 20%e0
- Qualifier
- autumne0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In spring, there was no effect of elevated [CO2] on photosynthetic capacity of leaves, but in autumn both Vc,max and Jmax were reduced by approximately 20% in elevated [CO2].”
e1“the photosynthetic response of T. repens”
Claim · model-written summary
Autumn Jmax fell by approximately 20% under elevated carbon dioxide.
- Taxon
- T. repensTrifolium repense0e1
- Treatment
- elevated [CO2]e0
- Outcome
- Jmaxe0
- Direction
- reducede0
- Value
- approximately 20%e0
- Qualifier
- autumne0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In spring, there was no effect of elevated [CO2] on photosynthetic capacity of leaves, but in autumn both Vc,max and Jmax were reduced by approximately 20% in elevated [CO2].”
e1“the photosynthetic response of T. repens”
Claim · model-written summary
The results indicate photosynthetic acclimation can occur in a nitrogen-fixing species in the field.
- Taxon
- T. repensTrifolium repense0e1
- Outcome
- acclimation of photosynthetic capacitye0
- Qualifier
- no artificial restrictions on sink capacitye0
- Setting
- fielde0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The results show that acclimation of photosynthetic capacity can occur in a nitrogen-fixing species, in the field where there are no artificial restrictions on sink capacity.”
e1“the photosynthetic response of T. repens”
The same questions in other papers
co2 · physiology: photosynthesis · Trifolium repens (white clover)Positive and negative results
1 paper in the same direction as this paper · 6 in the opposite direction
- positive
- positive
- positive
4 papers more in this group
See all 8 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.