Abstract
Geranium plants were grown from seed in chambers maintained at 350 or 1000 μL∙L −1 CO 2 . Phtopsynthesis as affected by leaf age and by leaf position was determined. Elevated CO 2 enhanced photosynthesis to the greatest extent in middle-aged leaves; very young leaves exhibited little enhancement, and net photosynthesis in the oldest leaves was depressed by elevated CO 2 . Temporary increases in net photosynthesis (relative to leaves developed at high CO 2 ) resulted when young leaves grown at 350 μL∙L −1 CO 2 were switched to 1000 μL∙L −1 CO 2 . Leaves switched later in development exhibited permanent enhancement. Middle-aged leaves exhibited a temporary depression followed by permanent enhancement. Leaves developed at high CO 2 and switched to low CO 2 did not exhibit any photosynthetic depression relative to plants grown continuously at low CO 2 . Similarly, leaves developed at low CO 2 , switched to high CO 2 for various lengths of time, and returned to low CO 2 showed no photosynthetic depression. Leaves developed at low CO 2 and switched to high CO 2 exhibited increases in specific leaf weight and leaf thickness. The increase in leaf thickness was proportional to length of time spent at high CO 2 . High CO 2 depressed the rate at which stomata developed but did not affect final stomatal density. Results suggest that photosynthesis at low CO 2 was limited by CO 2 regardless of developmental environment, whereas photosynthesis at high CO 2 was limited by the developmental characteristics of the leaf. Further, both biochemical and structural modifications appear to be involved in this response. Because of the very different responses of young versus old leaves, future studies should be careful to consider leaf age in assessing response to elevated CO 2 . Key words: carbon dioxide, elevated CO 2 , photosynthesis, geranium.
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Claims 12
Claim · model-written summary
Elevated CO2 enhanced photosynthesis most in middle-aged leaves.
GeraniumNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Elevated CO 2 enhanced photosynthesis to the greatest extent in middle-aged leaves”
t0“geranium”
Claim · model-written summary
Very young leaves showed little photosynthetic enhancement under elevated CO2.
- Organ / stage
- very young leavese0
- Treatment
- Elevated CO 2e0
- Outcome
- photosynthesise0
- Direction
- little enhancemente0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Elevated CO 2 enhanced photosynthesis to the greatest extent in middle-aged leaves; very young leaves exhibited little enhancement”
t0“geranium”
Claim · model-written summary
Elevated CO2 depressed photosynthesis in oldest leaves.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“net photosynthesis in the oldest leaves was depressed by elevated CO 2”
t0“geranium”
Claim · model-written summary
Young leaves switched from low to high CO2 had temporary net photosynthetic increases.
- Organ / stage
- young leavese0
- Treatment
- switched to 1000 μL∙L −1 CO 2e0
- Outcome
- net photosynthesise0
- Direction
- increasese0
- Qualifier
- Temporarye0
- Comparator
- leaves developed at high CO 2e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Temporary increases in net photosynthesis (relative to leaves developed at high CO 2 ) resulted when young leaves grown at 350 μL∙L −1 CO 2 were switched to 1000 μL∙L −1 CO 2 .”
t0“geranium”
Claim · model-written summary
Leaves switched later in development had permanent photosynthetic enhancement.
- Organ / stage
- Leaves switched later in developmente0
- Treatment
- switched to 1000 μL∙L −1 CO 2e0
- Outcome
- net photosynthesise0
- Direction
- enhancemente0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Temporary increases in net photosynthesis (relative to leaves developed at high CO 2 ) resulted when young leaves grown at 350 μL∙L −1 CO 2 were switched to 1000 μL∙L −1 CO 2 . Leaves switched later in development exhibited permanent enhancement.”
t0“geranium”
Claim · model-written summary
Middle-aged leaves had transient depression followed by permanent photosynthetic enhancement.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Middle-aged leaves exhibited a temporary depression followed by permanent enhancement.”
t0“geranium”
Claim · model-written summary
Leaves developed at high CO2 then switched to low CO2 showed no photosynthetic depression relative to continuously low CO2 plants.
- Treatment
- switched to low CO 2e0
- Outcome
- photosynthetic depressione0
- Direction
- did not exhibite0
- Comparator
- plants grown continuously at low CO 2e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Leaves developed at high CO 2 and switched to low CO 2 did not exhibit any photosynthetic depression relative to plants grown continuously at low CO 2 .”
t0“geranium”
Claim · model-written summary
Leaves switched low to high and back to low CO2 showed no photosynthetic depression.
- Treatment
- switched to high CO 2 for various lengths of time, and returned to low CO 2e0
- Outcome
- photosynthetic depressione0
- Direction
- no photosynthetic depressione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“leaves developed at low CO 2 , switched to high CO 2 for various lengths of time, and returned to low CO 2 showed no photosynthetic depression.”
t0“geranium”
Claim · model-written summary
Switching low-CO2 leaves to high CO2 increased specific leaf weight and thickness.
- Treatment
- switched to high CO 2e0
- Outcome
- specific leaf weight and leaf thicknesse0
- Direction
- increasese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Leaves developed at low CO 2 and switched to high CO 2 exhibited increases in specific leaf weight and leaf thickness.”
t0“geranium”
Claim · model-written summary
Leaf thickness increase was proportional to duration at high CO2.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The increase in leaf thickness was proportional to length of time spent at high CO 2 .”
t0“geranium”
Claim · model-written summary
High CO2 slowed stomatal development.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“High CO 2 depressed the rate at which stomata developed”
t0“geranium”
Claim · model-written summary
High CO2 did not change final stomatal density.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“High CO 2 depressed the rate at which stomata developed but did not affect final stomatal density.”
t0“geranium”
The same questions in other papers
co2 · growth · GeraniumPositive and negative results
1 paper in the same direction as this paper · 1 in the opposite direction
- no effect
- positive
co2 · physiology: gas exchange · GeraniumResults agree
1 paper in the same direction as this paper
- no effect
co2 · physiology: photosynthesis · GeraniumResults agree
1 paper in the same direction as this paper
- positive
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.