Abstract
SUMMARY Hybrid poplar ( Populus tristis Fisch. × P. balsamifera L., cv. Tristis) and sugar maple ( Acer saccharum Marsh.) seedlings were grown under contrasting light and ozone treatments to investigate the role of the light environment in their response to chronic ozone stress. In consecutive growth chamber experiments, cuttings of shade‐intolerant poplar and 3‐yr‐old seedlings of shade‐tolerant sugar maple were grown in pots for 6 and 10 wk, respectively, under shaded, low light irradiance ( c. 2.5 mol m −2 d −1 PPFD or 7% of full sunlight) and six‐fold greater irradiance ( c. 16.6 mol m −2 d −1 PPFD or 45% of full sunlight) in combination with low (< 10 nl 1 −1 ) and elevated levels of ozone ( c. 99–115 nl 1 −1 ). In unshaded poplar plants, ozone exposure reduced root dry mass by 33% at final harvest, while shaded plants had no such response. By comparison, sugar maple root dry mass was reduced by ozone in shaded plants by 10%, but was unaffected by ozone in unshaded plants. In poplar, leaf area: plant dry mass ratios were unaffected by ozone, whereas in sugar maple ozone‐exposed plants had a 24% lower leaf area: plant dry mass ratio in the shaded treatment. In shade‐grown sugar maple, ozone doubled dark respiration rates of leaves, but in unshaded seedlings ozone had no effect on respiration. In comparison, in poplar plants ozone exposure resulted in greater increases in dark respiration under unshaded than shaded conditions. In unshaded plants, ozone treatment resulted in lower in situ net photosynthesis in poplar, but not in sugar maple. Overall, shade‐grown sugar maple appeared more sensitive to ozone stress than unshaded plants in terms of lower leaf area: plant dry mass ratio and root growth and higher leaf respiration. In poplar on the other hand, root growth, leaf respiration and photosynthesis were more affected by ozone in unshaded than in shaded plants. These findings suggest that shade‐grown sugar maple and unshaded poplar may experience greater reductions in carbon gain and growth under elevated levels of ozone than plants under the opposite light conditions.
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Claims 7
Claim · model-written summary
Ozone reduced root dry mass of unshaded poplar by 33% at final harvest, while shaded poplar showed no such response.
- Treatment
- ozone exposuree1
- Outcome
- root dry masse1
- Direction
- reducede1
- Value
- 33%e1
- Comparator
- shaded plantse1
PopulusOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“In unshaded poplar plants, ozone exposure reduced root dry mass by 33% at final harvest, while shaded plants had no such response”
Claim · model-written summary
Ozone reduced root dry mass of shaded sugar maple by 10%, while unshaded sugar maple was unaffected.
- Taxon
- sugar maple
Acer saccharume2 - Treatment
- ozonee2
- Outcome
- root dry masse2
- Direction
- reducede2
- Value
- 10%e2
- Comparator
- unshaded plantse2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“By comparison, sugar maple root dry mass was reduced by ozone in shaded plants by 10%, but was unaffected by ozone in unshaded plants”
Claim · model-written summary
Ozone-exposed shaded sugar maple had a 24% lower leaf area: plant dry mass ratio.
- Taxon
- sugar mapleAcer saccharume3
- Treatment
- ozonee3
- Outcome
- leaf area: plant dry mass ratioe3
- Direction
- lowere3
- Value
- 24%e3
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e3“in sugar maple ozone‐exposed plants had a 24% lower leaf area: plant dry mass ratio in the shaded treatment”
Claim · model-written summary
Ozone doubled dark respiration of leaves in shade-grown sugar maple, but had no effect in unshaded seedlings.
- Taxon
- sugar mapleAcer saccharume4
- Treatment
- ozonee4
- Outcome
- dark respiration rates of leavese4
- Direction
- doublede4
- Comparator
- unshaded seedlingse4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e4“In shade‐grown sugar maple, ozone doubled dark respiration rates of leaves, but in unshaded seedlings ozone had no effect on respiration”
Claim · model-written summary
Ozone caused greater increases in dark respiration of poplar under unshaded than shaded conditions.
- Treatment
- ozone exposuree5
- Outcome
- dark respiratione5
- Direction
- greater increasese5
- Comparator
- shaded conditionse5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e5“In poplar plants ozone exposure resulted in greater increases in dark respiration under unshaded than shaded conditions”
Claim · model-written summary
In unshaded poplar, ozone lowered in situ net photosynthesis, but not in sugar maple.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e6“In unshaded plants, ozone treatment resulted in lower in situ net photosynthesis in poplar, but not in sugar maple”
Claim · model-written summary
Ozone did not change the leaf area: plant dry mass ratio of poplar.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e7“In poplar, leaf area: plant dry mass ratios were unaffected by ozone”
The same questions in other papers
ozone · growth · Acer saccharum (sugar maple)Results differ
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2 papers in the same direction as this paper
- negative
- negative
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.