Abstract
CO2 concentrations in the Earth’s atmosphere will rise to between 550 and 700 µL L–1 by 2100 (IPCC 2001). In much of the world, ozone (O3) is the air pollutant most likely to be having adverse effects on the growth of plants. Here we describe the impacts of CO2 and O3 episodes (rising to 100 nL L–1), singly and in mixtures on the growth and physiology of an interamerican hybrid poplar (Populus trichocarpa L. (Torr. & Gray ex Hook.) × P. deltoids Bartr. ex Marsh). 700 µL L–1 CO2 increased all growth variables relative to values in 350 µL L–1. Mainstem dry weight showed a 38% increase in year 1 and a 32% increase in year 2. Ozone episodes reduced mainstem dry mass by 45% in 350 µL L–1 CO2 and by 34% in 700 µL L–1 CO2. A / Ci analysis showed limited effects on photosynthetic efficiency of 700 µL L–1 CO2 but in contrast, Vcmax was reduced by O3 episodes. CO2 tended to increase leaf expansion but O3 episodes reduced expansion rates generally although a short period of increased leaf expansion in response to O3 was also observed. O3 reduced leaf solute potentials (?s) and increased turgor (P) in young leaves. Cell wall properties (elasticity and plasticity) were both stimulated by ozone and this was associated with increased leaf expansion. A new mechanism is proposed which suggests that O3 may act directly on the cell wall, attacking polysaccharides in the wall that result in altered cell wall properties and leaf growth. O3 episodes increased leaf loss, elevated CO2 delayed abscission and O3 was less effective at accelerating leaf loss in elevated CO2. Overall CO2 increased growth, O3 caused decreases and the treatment combination gave intermediate effects. Thus O3 episodes are less likely to be detrimental to P. trichocarpa × P. deltoides in the CO2 concentrations of the future.
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Claims 18
Claim · model-written summary
Elevated CO2 increased all measured growth variables.
PopulusOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“700 µL L–1 CO2 increased all growth variables relative to values in 350 µL L–1”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Elevated CO2 increased mainstem dry weight by 38% in year 1.
- Treatment
- 700 µL L–1 CO2e1
- Outcome
- Mainstem dry weighte0
- Direction
- increasee0
- Value
- 38%e0
- Comparator
- 350 µL L–1e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Mainstem dry weight showed a 38% increase in year 1”
e1“700 µL L–1 CO2 increased all growth variables relative to values in 350 µL L–1”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Elevated CO2 increased mainstem dry weight by 32% in year 2.
- Treatment
- 700 µL L–1 CO2e1
- Outcome
- Mainstem dry weighte0
- Direction
- increasee0
- Value
- 32%e0
- Comparator
- 350 µL L–1e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Mainstem dry weight showed a 38% increase in year 1 and a 32% increase in year 2”
e1“700 µL L–1 CO2 increased all growth variables relative to values in 350 µL L–1”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Ozone reduced mainstem dry mass by 45% under ambient CO2.
- Treatment
- Ozone episodese0
- Outcome
- mainstem dry masse0
- Direction
- reducede0
- Value
- 45%e0
- Qualifier
- 350 µL L–1 CO2e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Ozone episodes reduced mainstem dry mass by 45% in 350 µL L–1 CO2”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Ozone reduced mainstem dry mass by 34% under elevated CO2.
- Treatment
- Ozone episodese0
- Outcome
- mainstem dry masse0
- Direction
- reducede0
- Value
- 34%e0
- Qualifier
- 700 µL L–1 CO2e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Ozone episodes reduced mainstem dry mass by 45% in 350 µL L–1 CO2 and by 34% in 700 µL L–1 CO2”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Elevated CO2 had limited effects on photosynthetic efficiency.
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A / Ci analysis showed limited effects on photosynthetic efficiency of 700 µL L–1 CO2”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Ozone episodes reduced Vcmax.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Vcmax was reduced by O3 episodes”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Elevated CO2 tended to increase leaf expansion.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“CO2 tended to increase leaf expansion”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Ozone generally reduced leaf expansion rates.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“O3 episodes reduced expansion rates generally”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Ozone briefly increased leaf expansion.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a short period of increased leaf expansion in response to O3 was also observed”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Ozone reduced leaf solute potentials in young leaves.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“O3 reduced leaf solute potentials (?s) and increased turgor (P) in young leaves”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Ozone increased turgor in young leaves.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“O3 reduced leaf solute potentials (?s) and increased turgor (P) in young leaves”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Ozone stimulated cell wall elasticity and plasticity.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Cell wall properties (elasticity and plasticity) were both stimulated by ozone”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Stimulated cell wall properties were associated with increased leaf expansion.
- Treatment
- ozonee0
- Outcome
- leaf expansione0
- Direction
- increasede0
- Qualifier
- Cell wall properties (elasticity and plasticity)e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Cell wall properties (elasticity and plasticity) were both stimulated by ozone and this was associated with increased leaf expansion”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Ozone increased leaf loss.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“O3 episodes increased leaf loss”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Elevated CO2 delayed abscission.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“elevated CO2 delayed abscission”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Ozone accelerated leaf loss less under elevated CO2.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“O3 was less effective at accelerating leaf loss in elevated CO2”
t0“poplar (Populus trichocarpa × P. deltoides)”
Claim · model-written summary
Combined CO2 and ozone treatment had intermediate growth effects.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Overall CO2 increased growth, O3 caused decreases and the treatment combination gave intermediate effects”
t0“poplar (Populus trichocarpa × P. deltoides)”
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