Abstract
Abstract A South African C4-dominated grassland was exposed to twice-ambient atmospheric CO2 concentration using gas emitted by a natural CO2 spring and distributed over a 7m x 7m plot. A similar control plot was established 20m away at near-ambient CO2 concentrations. Photosynthetic CO2 response curves were performed on three C4 and one C3 grass species under both treatments, in spring (post-fire), mid-summer and autumn. Photosynthetic efficiency of the post-fire dominants, Alloteropsis semialata subsp. eckloniana (C3) and Andropogon appendiculatus (C4) was significantly enhanced in high CO2 only during the early season, when photosynthetic capacity was high. Thereafter, photosynthetic capacity decreased with advancing season in both species, and positive responses to high CO2 were lost or reduced. In the mid- to late-season dominant Themeda triandra (C4), photosynthetic capacity was maintained in elevated CO2 during the mid- to late-season, while decreasing in ambient CO2 relative to high CO2. Eragrostis racemosa (C4), a slow grower, showed no significant responses to high CO2 during the late season. CO2-responsiveness in the field generally followed the seasonal phenologies of each species, being greatest during the most active growth period. Keywords: CLIMATE CHANGEGAS EXCHANGEPHOTOSYNTHETIC REGULATIONSTOMATAL CONDUCTANCE
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Claims 6
Claim · model-written summary
High CO2 significantly enhanced early season photosynthetic efficiency in Alloteropsis semialata.
- Taxon
- Alloteropsis semialata subsp. eckloniana
Alloteropsis semialata subsp. ecklonianae0 - Treatment
- high CO2e0
- Outcome
- Photosynthetic efficiencye0
- Direction
- enhancede0
- Qualifier
- only during the early seasone0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Photosynthetic efficiency of the post-fire dominants, Alloteropsis semialata subsp. eckloniana (C3) and Andropogon appendiculatus (C4) was significantly enhanced in high CO2 only during the early season”
Claim · model-written summary
High CO2 significantly enhanced early season photosynthetic efficiency in Andropogon appendiculatus.
- Taxon
- Andropogon appendiculatus
Andropogon appendiculatuse0 - Treatment
- high CO2e0
- Outcome
- Photosynthetic efficiencye0
- Direction
- enhancede0
- Qualifier
- only during the early seasone0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Photosynthetic efficiency of the post-fire dominants, Alloteropsis semialata subsp. eckloniana (C3) and Andropogon appendiculatus (C4) was significantly enhanced in high CO2 only during the early season”
Claim · model-written summary
Photosynthetic capacity of Alloteropsis semialata declined as the season advanced.
- Taxon
- Alloteropsis semialata subsp. ecklonianaAlloteropsis semialata subsp. ecklonianae1
- Outcome
- photosynthetic capacitye0
- Direction
- decreasede0
- Setting
- advancing seasone0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Thereafter, photosynthetic capacity decreased with advancing season in both species”
e1“Alloteropsis semialata subsp. eckloniana (C3) and Andropogon appendiculatus (C4)”
Claim · model-written summary
Photosynthetic capacity of Andropogon appendiculatus declined as the season advanced.
- Taxon
- Andropogon appendiculatusAndropogon appendiculatuse1
- Outcome
- photosynthetic capacitye0
- Direction
- decreasede0
- Setting
- advancing seasone0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Thereafter, photosynthetic capacity decreased with advancing season in both species”
e1“Alloteropsis semialata subsp. eckloniana (C3) and Andropogon appendiculatus (C4)”
Claim · model-written summary
Elevated CO2 maintained Themeda triandra photosynthetic capacity in mid to late season while ambient capacity fell.
- Taxon
- Themeda triandra
Themeda triandrae0 - Treatment
- elevated CO2e0
- Outcome
- photosynthetic capacitye0
- Direction
- maintainede0
- Comparator
- ambient CO2e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In the mid- to late-season dominant Themeda triandra (C4), photosynthetic capacity was maintained in elevated CO2 during the mid- to late-season, while decreasing in ambient CO2 relative to high CO2”
Claim · model-written summary
Eragrostis racemosa had no significant response to high CO2 in late season.
- Taxon
- Eragrostis racemosa
Eragrostis racemosae0 - Treatment
- high CO2e0
- Outcome
- responsese0
- Direction
- no significant responsese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eragrostis racemosa (C4), a slow grower, showed no significant responses to high CO2 during the late season”