Abstract
For most studies involving the response of plants to future concentrations of atmospheric carbon dioxide (CO2), a current concentration of 360–370 μatm is assumed, based on recent data obtained from the Mauna Loa observatory. In the present study, average seasonal diurnal values of ambient CO2 obtained at ground level from three global locations (Australia, Japan and the USA) indicated that the average CO2 (at canopy height) can vary from over 500 μatm at night to 350 μatm during the day with average 24-h values ranging from 390 to 465 μatm. At all sites sampled, ambient CO2 rose to a maximum value during the pre-dawn period (03.00–06.00 hours); at sunrise, CO2 remained elevated for several hours before declining to a steady-state concentration between 350 and 400 μatm by mid-morning (08.00–10.00 hours). Responses of plant growth to simulations of the observed variation of in situ CO2 were compared to growth at a constant CO2 concentration in controlled environment chambers. Three diurnal patterns were used (constant 370 μatm CO2, constant 370 during the day (07.00–19.00 hours), high CO2 (500 μatm) at night; or, high CO2 (500 μatm) at night and during the early morning (07.00–09.00 hours) decreasing to 370 μatm by 10.00 hours). Three plant species − soybean (Glycine max, L (Merr.), velvetleaf (Abutilon theophrasti L.) and tomato (Lycopersicon esculentum L.) − were grown in each of these environments. For soybean, high night-time CO2 resulted in a significant increase in net assimilation rate (NAR), plant growth, leaf area and biomass relative to a constant ambient value of CO2 by 29 days after sowing. Significant increases in NAR for all three species, and significant increases in leaf area, growth and total biomass for two of the three C3 species tested (velvetleaf and soybean) were also observed after 29 days post sowing for the high night/early morning diurnal pattern of CO2. Data from these experiments suggest that the ambient CO2 concentration experienced by some plants is higher than the Mauna Loa average, and that growth of some agricultural species at in situ CO2 levels can differ significantly from the constant CO2 value used as a control in many CO2 experiments. This suggests that a reassessment of control conditions used to quantify the response of plants to future, elevated CO2 may be required.
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Claims 7
Claim · model-written summary
Canopy-height ambient CO2 ranged from above 500 μatm at night to 350 μatm by day, with 24-hour means of 390 to 465 μatm.
Not reportedTaxon
Verbatim
e0“average CO2 (at canopy height) can vary from over 500 μatm at night to 350 μatm during the day with average 24-h values ranging from 390 to 465 μatm”
Claim · model-written summary
Ambient CO2 peaked before dawn and reached 350 to 400 μatm by mid-morning.
Not reportedTaxon
Verbatim
e0“ambient CO2 rose to a maximum value during the pre-dawn period (03.00–06.00 hours); at sunrise, CO2 remained elevated for several hours before declining to a steady-state concentration between 350 and 400 μatm by mid-morning (08.00–10.00 hours)”
Claim · model-written summary
High nighttime CO2 increased soybean net assimilation rate, growth, leaf area and biomass relative to constant ambient CO2 after 29 days.
- Taxon
- soybean
Glycine maxe0 - Treatment
- high night-time CO2e0
- Outcome
- net assimilation rate (NAR), plant growth, leaf area and biomasse0
- Direction
- increasee0
- Qualifier
- 29 days after sowinge0
- Comparator
- a constant ambient value of CO2e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“For soybean, high night-time CO2 resulted in a significant increase in net assimilation rate (NAR), plant growth, leaf area and biomass relative to a constant ambient value of CO2 by 29 days after sowing”
Claim · model-written summary
The high nighttime and early-morning CO2 pattern significantly increased NAR in soybean, velvetleaf and tomato.
- Taxon
- soybeanGlycine maxe1
- Treatment
- high night/early morning diurnal pattern of CO2e2
- Outcome
- NARe0
- Direction
- increasese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Significant increases in NAR for all three species”
e1“soybean (Glycine max, L (Merr.), velvetleaf (Abutilon theophrasti L.) and tomato (Lycopersicon esculentum L.)”
e2“high night/early morning diurnal pattern of CO2”
Claim · model-written summary
The high nighttime and early-morning CO2 pattern increased leaf area, growth and biomass in velvetleaf.
- Taxon
- velvetleaf
Abutilon theophrastie0 - Treatment
- high night/early morning diurnal pattern of CO2e0
- Outcome
- leaf area, growth and total biomasse0
- Direction
- increasese0
- Qualifier
- 29 days post sowinge0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Significant increases in NAR for all three species, and significant increases in leaf area, growth and total biomass for two of the three C3 species tested (velvetleaf and soybean) were also observed after 29 days post sowing for the high night/early morning diurnal pattern of CO2”
Claim · model-written summary
The high nighttime and early-morning CO2 pattern increased leaf area, growth and biomass in soybean.
- Taxon
- soybeanGlycine maxe0
- Treatment
- high night/early morning diurnal pattern of CO2e0
- Outcome
- leaf area, growth and total biomasse0
- Direction
- increasese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Significant increases in NAR for all three species, and significant increases in leaf area, growth and total biomass for two of the three C3 species tested (velvetleaf and soybean) were also observed after 29 days post sowing for the high night/early morning diurnal pattern of CO2”
Claim · model-written summary
The authors suggested reassessing control CO2 conditions for elevated CO2 experiments.
- Taxon
- plantsViridiplantaee0
- Outcome
- reassessment of control conditionse0
Verbatim
e0“a reassessment of control conditions used to quantify the response of plants to future, elevated CO2 may be required”
The same questions in other papers
co2 · growth · Abutilon theophrasti (velvetleaf)Positive and negative results
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- no effect
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See all 6 papers →co2 · growth · Glycine max (soybean)Positive and negative results
82 papers in the same direction as this paper · 16 in the opposite direction · 2 reporting no difference from an alternative
- no effect
- negative
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See all 101 papers →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.