Abstract
summary This study examined the effects of elevated ozone (O 3 ) and/or carbon dioxide (CO 2 ) on the diel allocation of photosynthetically fixed carbon in fully expanded leaves of young (growth stages 4–5) spring wheat (Triticum aestivum L. cv. Hanno). Plants were grown in controlled environment chambers and exposed to two O 3 regimes [‘non‐polluted’ air (CF), < 5 nmol mol −1 ; ‘polluted’ air, CF + 75 nmol mol −1 7 h d −1 ] and two CO 2 treatments (‘ambient’, 354/tmol mol −1 ; ‘elevated’, 700/μmol mol −1 ) over a 30 d period. Neutral sugars (predominantly sucrose) were found to be the most abundant form of carbohydrate accumulated by leaves during the day, but significant quantities of starch and high degree of polymerization (d.p.) fructans were also present. Elevated concentrations of O 3 and/or CO 2 were found to have marked effects on diel patterns of export, storage and respiration, whilst the proportions of fixed carbon allocated to each of these processes were broadly similar. O 3 depressed the rate of net CO 2 assimilation (−20%) and reduced stomatal conductance (−19%). This was reflected in a reduced amount of carbohydrate accumulated in, and exported by, source tissue during the day. Effects of O 3 on the rate of CO 2 fixation were aggravated by an increased demand for carbon by dark respiratory processes. In contrast, doubling the atmospheric concentration of CO 2 enhanced the rate of net CO 2 assimilation (+ 47%) and reduced the proportion of fixed carbon retained in the leaf blade, increasing the rate of export. The favourable carbon balance of CO 2 enriched leaves was further enhanced by a decrease in the cost of maintenance respiration, whilst simultaneous measurements of CO 2 efflux and O 2 uptake at night suggested a shift in the substrates metabolized at high CO 2 . Effects of elevated CO 2 and O 3 on the carbon balance of individual leaf blades over a single 24 h light/dark cycle were entirely consistent with the cumulative effects of the gases on plant growth over a 30 d period. O 3 reduced the rate of plant growth (− 10%), but there were differential effects of O 3 on the growth of root and shoot which exacerbated the decrease in assimilate availability induced by O 3 . In contrast the favourable effects of CO 2 enrichment on the carbon balance of individual source leaves was reflected in the enhanced accumulation of dry matter in existing sinks, and the initiation of new sinks (i.e. increased tillering). In the combined treatment (elevated CO 2 + O 3 ), O 3 counteracted the favourable effects of CO, enrichment on the carbon balance of individual leaves, and the combined effects of the individual gases on the diel partitioning of photosynthetically fixed carbon in fully expanded leaf blades was reflected in a decreased rate of plant growth at elevated CO 2 , a situation further exacerbated by O 3 ‐induced shifts in the relative partitioning of carbon between root and shoot. There was no evidence that CO., enrichment afforded additional protection against O 3 damage: the extent of the O 3 ‐induced reduction in photosynthesis, carbohydrate availability and growth observed at elevated CO 2 was similar to that induced by O., in ambient air, despite additive effects of the gases on stomatal conductance that would reduce the effective dose of O 3 by ? 30%. The wider ecological significance of interactions between elevated CO 2 and O 3 is discussed in the light of other recent findings.
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Claims 17
Claim · model-written summary
Neutral sugars were the most abundant daytime leaf carbohydrates; starch and fructans were also present.
- Taxon
- spring wheat
Triticum aestivume1 - Organ / stage
- leavese0
- Outcome
- most abundant form of carbohydratee0
- Qualifier
- starch and high degree of polymerization (d.p.) fructans were also presente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Neutral sugars (predominantly sucrose) were found to be the most abundant form of carbohydrate accumulated by leaves during the day, but significant quantities of starch and high degree of polymerization (d.p.) fructans were also present.”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Elevated ozone and/or carbon dioxide markedly altered diel export, storage and respiration patterns while allocation proportions were broadly similar.
- Taxon
- spring wheatTriticum aestivume1
- Treatment
- Elevated concentrations of O 3 and/or CO 2e0
- Outcome
- diel patterns of export, storage and respiratione0
- Qualifier
- proportions of fixed carbon allocated to each of these processes were broadly similare0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Elevated concentrations of O 3 and/or CO 2 were found to have marked effects on diel patterns of export, storage and respiration, whilst the proportions of fixed carbon allocated to each of these processes were broadly similar.”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Ozone depressed net carbon dioxide assimilation by 20%.
- Taxon
- spring wheatTriticum aestivume1
- Treatment
- O 3e0
- Outcome
- rate of net CO 2 assimilatione0
- Direction
- depressede0
- Value
- −20%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“O 3 depressed the rate of net CO 2 assimilation (−20%)”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Ozone reduced stomatal conductance by 19%.
- Taxon
- spring wheatTriticum aestivume1
- Treatment
- O 3e0
- Outcome
- stomatal conductancee0
- Direction
- reducede0
- Value
- −19%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“O 3 depressed the rate of net CO 2 assimilation (−20%) and reduced stomatal conductance (−19%).”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Ozone reduced daytime carbohydrate accumulation and export from source tissue.
- Taxon
- spring wheatTriticum aestivume2
- Treatment
- O 3e1
- Outcome
- carbohydrate accumulated in, and exported by, source tissuee0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This was reflected in a reduced amount of carbohydrate accumulated in, and exported by, source tissue during the day.”
e1“O 3 depressed the rate of net CO 2 assimilation”
e2“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Increased demand for carbon by dark respiration aggravated the ozone effect on carbon fixation.
- Taxon
- spring wheatTriticum aestivume1
- Treatment
- O 3e0
- Outcome
- rate of CO 2 fixatione0
- Qualifier
- increased demand for carbon by dark respiratory processese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Effects of O 3 on the rate of CO 2 fixation were aggravated by an increased demand for carbon by dark respiratory processes.”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Elevated carbon dioxide enhanced net assimilation by 47%.
- Taxon
- spring wheatTriticum aestivume1
- Treatment
- doubling the atmospheric concentration of CO 2e0
- Outcome
- rate of net CO 2 assimilatione0
- Direction
- enhancede0
- Value
- + 47%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“doubling the atmospheric concentration of CO 2 enhanced the rate of net CO 2 assimilation (+ 47%)”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Elevated carbon dioxide reduced fixed carbon retention in the blade and increased export.
- Taxon
- spring wheatTriticum aestivume2
- Treatment
- doubling the atmospheric concentration of CO 2e1
- Outcome
- proportion of fixed carbon retained in the leaf bladee0
- Direction
- reducede0
- Qualifier
- increasing the rate of exporte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“reduced the proportion of fixed carbon retained in the leaf blade, increasing the rate of export.”
e1“doubling the atmospheric concentration of CO 2”
e2“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Carbon dioxide enrichment decreased maintenance respiration costs.
- Taxon
- spring wheatTriticum aestivume1
- Treatment
- CO 2 enrichede0
- Outcome
- cost of maintenance respiratione0
- Direction
- decreasee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The favourable carbon balance of CO 2 enriched leaves was further enhanced by a decrease in the cost of maintenance respiration”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Night gas exchange suggested a shift in metabolized substrates at high carbon dioxide.
- Taxon
- spring wheatTriticum aestivume1
- Treatment
- high CO 2e0
- Outcome
- shift in the substrates metabolizede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“simultaneous measurements of CO 2 efflux and O 2 uptake at night suggested a shift in the substrates metabolized at high CO 2”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Ozone reduced plant growth by 10%.
- Taxon
- spring wheatTriticum aestivume1
- Treatment
- O 3e0
- Outcome
- rate of plant growthe0
- Direction
- reducede0
- Value
- − 10%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“O 3 reduced the rate of plant growth (− 10%)”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Ozone differentially affected root and shoot growth.
- Taxon
- spring wheatTriticum aestivume1
- Treatment
- O 3e0
- Outcome
- growth of root and shoote0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“there were differential effects of O 3 on the growth of root and shoot”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Carbon dioxide enrichment enhanced dry matter accumulation in existing sinks and increased tillering.
- Taxon
- spring wheatTriticum aestivume2
- Treatment
- CO 2 enrichmente1
- Outcome
- accumulation of dry matter in existing sinkse0
- Direction
- enhancede0
- Qualifier
- increased tilleringe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“enhanced accumulation of dry matter in existing sinks, and the initiation of new sinks (i.e. increased tillering)”
e1“CO 2 enrichment”
e2“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Ozone counteracted the favorable leaf carbon balance under elevated carbon dioxide.
- Taxon
- spring wheatTriticum aestivume1
- Treatment
- O 3e0
- Outcome
- carbon balance of individual leavese0
- Direction
- counteractede0
- Comparator
- CO, enrichmente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“O 3 counteracted the favourable effects of CO, enrichment on the carbon balance of individual leaves”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
The combined gases decreased growth under elevated carbon dioxide.
- Taxon
- spring wheatTriticum aestivume2
- Treatment
- elevated CO 2 + O 3e1
- Outcome
- rate of plant growthe0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a decreased rate of plant growth at elevated CO 2”
e1“In the combined treatment (elevated CO 2 + O 3 )”
e2“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Carbon dioxide enrichment offered no additional protection from ozone damage in photosynthesis, carbohydrate availability or growth.
- Taxon
- spring wheatTriticum aestivume1
- Treatment
- CO., enrichmente0
- Outcome
- photosynthesis, carbohydrate availability and growthe0
- Direction
- similare0
- Comparator
- ambient aire0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“There was no evidence that CO., enrichment afforded additional protection against O 3 damage: the extent of the O 3 ‐induced reduction in photosynthesis, carbohydrate availability and growth observed at elevated CO 2 was similar to that induced by O., in ambient air”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
Claim · model-written summary
Combined gases had additive effects on stomatal conductance that would reduce effective ozone dose by about 30%.
- Taxon
- spring wheatTriticum aestivume1
- Outcome
- stomatal conductancee0
- Qualifier
- reduce the effective dose of O 3 by ? 30%e0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“additive effects of the gases on stomatal conductance that would reduce the effective dose of O 3 by ? 30%”
e1“spring wheat (Triticum aestivum L. cv. Hanno)”
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See all 145 papers →8 of 9 groups shown: named compounds and organisms first, then groups whose results differ (checked claim by claim), then those with positive and negative results, then the smaller groups.
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.