Abstract
Arguments based on the biochemistry of photosynthesis predict a positive interaction between elevated atmospheric [CO2] and temperature on photosynthesis as well as growth. In contrast, few long-term studies on trees find greater stimulation of photosynthesis in response to elevated [CO2] at warmer compared with cooler temperatures. To test for CO2 × temperature interactions on leaf photosynthesis and whole-plant growth, we planted Eucalyptus globulus Labill. in climate-controlled chambers in the field at the Hawkesbury Forest Experiment research site, and investigated how photosynthetic enhancement changed across a range of seasonal temperatures. Trees were grown in a complete two-way factorial design with two CO2 concentrations (ambient and ambient + 240 ppm) and two temperatures (ambient and ambient + 3 °C) for 15 months until they reached ∼10 m height, after which they were harvested for biomass. There was significant enhancement of photosynthesis and growth with elevated [CO2], with the photosynthetic stimulation varying with season, but there was no significant effect of warming. Photosynthetic enhancement was higher in summer (+46% at 28 °C) than in winter (+14% at 20 °C). Photosynthetic enhancement as a function of leaf temperature was consistent with theoretical expectations, but was strongly mediated by the intercellular [CO2]/ambient [CO2] (Ci/Ca) ratio across seasons. Total tree biomass after 15 months was 66% larger in elevated CO2 (P = 0.017) with no significant warming effect detected. The fraction of biomass in coarse roots was reduced in warmed trees compared with ambient temperature controls, but there was no evidence of changed biomass allocation patterns in elevated CO2. We conclude that there are strong and consistent elevated CO2 effects on photosynthesis and biomass of E. globulus. It is crucial to consider stomatal conductance under a range of conditions to appraise the interactive effect of [CO2] and temperature on photosynthetic enhancement and subsequent implications for tree growth and forest productivity in future climates.
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Claims 11
Claim · model-written summary
Elevated CO2 significantly enhanced photosynthesis.
- Taxon
- Eucalyptus globulus Labill.
Eucalyptus globuluse0 - Treatment
- elevated [CO2]e1
- Outcome
- photosynthesise1
- Direction
- enhancemente1
- Comparator
- ambiente2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus globulus Labill.”
e1“There was significant enhancement of photosynthesis and growth with elevated [CO2]”
e2“two CO2 concentrations (ambient and ambient + 240 ppm) and two temperatures (ambient and ambient + 3 °C)”
Claim · model-written summary
Elevated CO2 significantly enhanced growth.
- Taxon
- Eucalyptus globulus Labill.Eucalyptus globuluse0
- Treatment
- elevated [CO2]e1
- Outcome
- growthe1
- Direction
- enhancemente1
- Comparator
- ambiente2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus globulus Labill.”
e1“There was significant enhancement of photosynthesis and growth with elevated [CO2]”
e2“two CO2 concentrations (ambient and ambient + 240 ppm) and two temperatures (ambient and ambient + 3 °C)”
Claim · model-written summary
Warming had no significant effect on photosynthetic enhancement or growth.
- Taxon
- Eucalyptus globulus Labill.Eucalyptus globuluse0
- Treatment
- warminge1
- Outcome
- effect of warminge1
- Comparator
- ambiente2
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus globulus Labill.”
e1“there was no significant effect of warming”
e2“two CO2 concentrations (ambient and ambient + 240 ppm) and two temperatures (ambient and ambient + 3 °C)”
Claim · model-written summary
Photosynthetic enhancement was 46% in summer at 28 °C, higher than in winter.
- Taxon
- Eucalyptus globulus Labill.Eucalyptus globuluse0
- Outcome
- Photosynthetic enhancemente1
- Direction
- highere1
- Value
- +46%e1
- Qualifier
- 28 °Ce1
- Comparator
- wintere1
- Setting
- summere1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus globulus Labill.”
e1“Photosynthetic enhancement was higher in summer (+46% at 28 °C) than in winter (+14% at 20 °C).”
Claim · model-written summary
Photosynthetic enhancement was 14% in winter at 20 °C, lower than in summer.
- Taxon
- Eucalyptus globulus Labill.Eucalyptus globuluse0
- Outcome
- Photosynthetic enhancemente1
- Direction
- lowerinferrede1
- Value
- +14%e1
- Qualifier
- 20 °Ce1
- Comparator
- summere1
- Setting
- wintere1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus globulus Labill.”
e1“Photosynthetic enhancement was higher in summer (+46% at 28 °C) than in winter (+14% at 20 °C).”
Claim · model-written summary
Leaf-temperature variation in CO2 photosynthetic enhancement matched theoretical expectations.
- Taxon
- Eucalyptus globulus Labill.Eucalyptus globuluse0
- Organ / stage
- leafe1
- Outcome
- Photosynthetic enhancemente1
- Qualifier
- consistent with theoretical expectationse1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus globulus Labill.”
e1“Photosynthetic enhancement as a function of leaf temperature was consistent with theoretical expectations”
Claim · model-written summary
Seasonal Ci/Ca ratio strongly mediated photosynthetic enhancement.
- Taxon
- Eucalyptus globulus Labill.Eucalyptus globuluse0
- Outcome
- Photosynthetic enhancemente1
- Qualifier
- intercellular [CO2]/ambient [CO2] (Ci/Ca) ratio across seasonse1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus globulus Labill.”
e1“Photosynthetic enhancement as a function of leaf temperature was consistent with theoretical expectations, but was strongly mediated by the intercellular [CO2]/ambient [CO2] (Ci/Ca) ratio across seasons.”
Claim · model-written summary
Total biomass was 66% larger under elevated CO2 after 15 months.
- Taxon
- Eucalyptus globulus Labill.Eucalyptus globuluse0
- Treatment
- elevated CO2e1
- Outcome
- Total tree biomasse1
- Direction
- largere1
- Value
- 66%e1
- Qualifier
- after 15 monthse1
- Comparator
- ambiente2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus globulus Labill.”
e1“Total tree biomass after 15 months was 66% larger in elevated CO2 (P = 0.017)”
e2“two CO2 concentrations (ambient and ambient + 240 ppm) and two temperatures (ambient and ambient + 3 °C)”
Claim · model-written summary
Warming had no statistically significant effect on total biomass.
- Taxon
- Eucalyptus globulus Labill.Eucalyptus globuluse0
- Treatment
- warminge1
- Outcome
- Total tree biomasse1
- Comparator
- ambiente2
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus globulus Labill.”
e1“Total tree biomass after 15 months was 66% larger in elevated CO2 (P = 0.017) with no significant warming effect detected.”
e2“two CO2 concentrations (ambient and ambient + 240 ppm) and two temperatures (ambient and ambient + 3 °C)”
Claim · model-written summary
Warming reduced the coarse-root share of biomass relative to ambient temperature.
- Taxon
- Eucalyptus globulus Labill.Eucalyptus globuluse0
- Organ / stage
- coarse rootse1
- Treatment
- warmed treese1
- Outcome
- fraction of biomass in coarse rootse1
- Direction
- reducede1
- Comparator
- ambient temperature controlse1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus globulus Labill.”
e1“The fraction of biomass in coarse roots was reduced in warmed trees compared with ambient temperature controls”
Claim · model-written summary
Elevated CO2 showed no evidence of changing biomass allocation patterns.
- Taxon
- Eucalyptus globulus Labill.Eucalyptus globuluse0
- Treatment
- elevated CO2e1
- Outcome
- biomass allocation patternse1
- Direction
- no evidence of changede1
- Comparator
- ambiente2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus globulus Labill.”
e1“there was no evidence of changed biomass allocation patterns in elevated CO2.”
e2“two CO2 concentrations (ambient and ambient + 240 ppm) and two temperatures (ambient and ambient + 3 °C)”
The same questions in other papers
co2 · growth · Eucalyptus globulus (blue gum)Positive and negative results
2 papers in the same direction as this paper · 1 in the opposite direction
- no effect
- positive
- positive
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1 paper in the same direction as this paper
- negative
co2 · physiology: photosynthesis · Eucalyptus globulus (blue gum)Results agree
2 papers in the same direction as this paper
- positive
- 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.