Abstract
Plant growth is typically stimulated at elevated carbon dioxide concentration ([CO2]), but a sustained and maximal stimulation of growth requires acquisition of additional N in proportion to the additional C fixed at elevated [CO2]. We hypothesized that legumes would be able to avoid N limitation at elevated [CO2]. Soybean was grown without N fertilizer from germination to final senescence at elevated [CO2] over two growing seasons under fully open-air conditions, providing a model legume system. Measurements of photosynthesis and foliar carbohydrate content showed that plants growing at elevated [CO2] had a c. 25% increase in the daily integral of photosynthesis and c. 58% increase in foliar carbohydrate content, suggesting that plants at elevated [CO2] had a surplus of photosynthate. Soybeans had a low leaf N content at the beginning of the season, which was a further c. 17% lower at elevated [CO2]. In the middle of the season, ureide, total amino acid and N content increased markedly, and the effect of elevated [CO2] on leaf N content disappeared. Analysis of individual amino acid levels supported the conclusion that plants at elevated [CO2] overcame an early-season N limitation. These soybean plants showed a c. 16% increase in dry mass at final harvest and showed no significant effect of elevated [CO2] on leaf N, protein or total amino acid content in the latter part of the season. One possible explanation for these findings is that N fixation had increased, and that these plants had acclimated to the increased N demand at elevated [CO2].
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Claims 9
Claim · model-written summary
Elevated CO2 increased daily photosynthesis integral by about 25%.
- Taxon
- Soybean
Glycine maxe1 - Treatment
- elevated [CO2]e0
- Outcome
- daily integral of photosynthesise0
- Direction
- increasee0
- Value
- c. 25%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“plants growing at elevated [CO2] had a c. 25% increase in the daily integral of photosynthesis”
e1“Soybean was grown without N fertilizer”
Claim · model-written summary
Elevated CO2 increased foliar carbohydrate content by about 58%.
- Taxon
- SoybeanGlycine maxe1
- Treatment
- elevated [CO2]e0
- Outcome
- foliar carbohydrate contente0
- Direction
- increasee0
- Value
- c. 58%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“plants growing at elevated [CO2] had a c. 25% increase in the daily integral of photosynthesis and c. 58% increase in foliar carbohydrate content”
e1“Soybean was grown without N fertilizer”
Claim · model-written summary
Early-season leaf nitrogen content was about 17% lower under elevated CO2.
- Taxon
- SoybeansGlycine maxe0
- Treatment
- elevated [CO2]e0
- Outcome
- leaf N contente0
- Direction
- lowere0
- Value
- c. 17%e0
- Qualifier
- beginning of the seasone0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soybeans had a low leaf N content at the beginning of the season, which was a further c. 17% lower at elevated [CO2]”
Claim · model-written summary
Midseason ureide, total amino acid and nitrogen contents increased markedly.
- Taxon
- SoybeanGlycine maxe1
- Outcome
- ureide, total amino acid and N contente0
- Direction
- increased markedlye0
- Qualifier
- middle of the seasone0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In the middle of the season, ureide, total amino acid and N content increased markedly”
e1“Soybean was grown without N fertilizer”
Claim · model-written summary
The elevated CO2 effect on leaf nitrogen content disappeared by midseason.
- Taxon
- SoybeanGlycine maxe1
- Treatment
- elevated [CO2]e0
- Outcome
- leaf N contente0
- Direction
- disappearede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the effect of elevated [CO2] on leaf N content disappeared”
e1“Soybean was grown without N fertilizer”
Claim · model-written summary
Individual amino acid levels supported that elevated CO2 plants overcame early nitrogen limitation.
- Taxon
- SoybeanGlycine maxe1
- Treatment
- elevated [CO2]e0
- Outcome
- overcame an early-season N limitatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Analysis of individual amino acid levels supported the conclusion that plants at elevated [CO2] overcame an early-season N limitation”
e1“Soybean was grown without N fertilizer”
Claim · model-written summary
Elevated CO2 increased final dry mass by about 16%.
- Taxon
- soybeanGlycine maxe0
- Treatment
- elevated [CO2]e2
- Outcome
- dry masse0
- Direction
- increasee0
- Value
- c. 16%e0
- Qualifier
- final harveste0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“These soybean plants showed a c. 16% increase in dry mass at final harvest”
e1“Soybean was grown without N fertilizer”
e2“at elevated [CO2] over two growing seasons”
Claim · model-written summary
Elevated CO2 had no significant late-season effect on leaf nitrogen, protein or total amino acid content.
- Taxon
- soybeanGlycine maxe1
- Treatment
- elevated [CO2]e0
- Outcome
- leaf N, protein or total amino acid contente0
- Direction
- no significant effecte0
- Qualifier
- latter part of the seasone0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“showed no significant effect of elevated [CO2] on leaf N, protein or total amino acid content in the latter part of the season”
e1“These soybean plants”
Claim · model-written summary
Authors propose increased nitrogen fixation as a possible explanation for acclimation to elevated CO2 nitrogen demand.
- Taxon
- soybeanGlycine maxe1
- Treatment
- elevated [CO2]e0
- Outcome
- acclimated to the increased N demande0
- Qualifier
- N fixation had increasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“One possible explanation for these findings is that N fixation had increased, and that these plants had acclimated to the increased N demand at elevated [CO2]”
e1“These soybean plants”
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