Abstract
Abstract. The diurnal cycling of leaf water potential (Ψ leaf ) in field‐grown sunflower ( Helianthus annuus ) was used to investigate the cause of water deficitinduced limitation of net photosynthesis. Daily midafternoon decreases in Ψ leaf of up to 1.5 MPa and in net photosynthesis of up to 50% were typical for irrigated sunflower during seed filling. These midafternoon values were lowered an additional 0.6 to 0.8 MPa by prolonged drought treatment. There was a nearly linear relationship between the decline in net photosynthesis and reductions in leaf conductance over the course of the day. Thus, it was unexpected to find that the low, midafternoon rates of photosynthesis were associated with the highest intercellular CO 2 concentrations. These and other observations suggest that the daily decline in photosynthesis represents a ‘down regulation’ of the biochemical demand for CO 2 that is coordinated with the diurnally developing need to conserve water, thus establishing a balanced limitation of photosynthesis involving both stomatal and non‐stomatal factors. There were no indications that either short term (i.e. diurnal declines in Ψ leaf ) or long term (i.e. drought treatment) water deficits caused any damage or malfunctioning of photosynthesis. Rather, both the daily declines in photosynthesis and the nearly 25% decrease in leaf area induced by prolonged drought appeared to be well‐controlled adaptive responses by field‐grown sunflower plants to limited water availability.
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Claims 8
Claim · model-written summary
Irrigated sunflower typically lost up to 1.5 MPa leaf water potential by midafternoon.
- Taxon
- sunflower
Helianthus annuuse0 - Outcome
- Ψ leafe0
- Direction
- decreasese0
- Value
- up to 1.5 MPae0
- Qualifier
- during seed fillinge0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Daily midafternoon decreases in Ψ leaf of up to 1.5 MPa and in net photosynthesis of up to 50% were typical for irrigated sunflower during seed filling”
Claim · model-written summary
Irrigated sunflower net photosynthesis typically fell up to 50% by midafternoon.
- Taxon
- sunflowerHelianthus annuuse0
- Outcome
- net photosynthesise0
- Direction
- decreasese0
- Value
- up to 50%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Daily midafternoon decreases in Ψ leaf of up to 1.5 MPa and in net photosynthesis of up to 50% were typical for irrigated sunflower during seed filling”
Claim · model-written summary
Prolonged drought lowered midafternoon leaf water potential another 0.6 to 0.8 MPa.
- Taxon
- sunflowerHelianthus annuust0
- Treatment
- prolonged drought treatmente0
- Outcome
- midafternoon valuese0
- Direction
- lowerede0
- Value
- 0.6 to 0.8 MPae0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“These midafternoon values were lowered an additional 0.6 to 0.8 MPa by prolonged drought treatment”
t0“sunflower”
Claim · model-written summary
Declining photosynthesis was nearly linearly related to reduced leaf conductance over the day.
- Taxon
- sunflowerHelianthus annuust0
- Organ / stage
- leafe0
- Outcome
- net photosynthesise0
- Direction
- declinee0
- Qualifier
- reductions in leaf conductancee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“There was a nearly linear relationship between the decline in net photosynthesis and reductions in leaf conductance over the course of the day”
t0“sunflower”
Claim · model-written summary
The lowest midafternoon photosynthesis rates coincided with the highest intercellular CO2 concentrations.
- Taxon
- sunflowerHelianthus annuust0
- Compound
- CO 2e0
- Outcome
- rates of photosynthesise0
- Direction
- lowe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the low, midafternoon rates of photosynthesis were associated with the highest intercellular CO 2 concentrations”
t0“sunflower”
Claim · model-written summary
The authors infer coordinated biochemical down-regulation and water conservation limit daily photosynthesis.
- Taxon
- sunflowerHelianthus annuust0
- Outcome
- daily decline in photosynthesise0
- Qualifier
- ‘down regulation’ of the biochemical demand for CO 2e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the daily decline in photosynthesis represents a ‘down regulation’ of the biochemical demand for CO 2 that is coordinated with the diurnally developing need to conserve water”
t0“sunflower”
Claim · model-written summary
Neither short nor long water deficits showed indications of photosynthetic damage or malfunction.
- Taxon
- sunflowerHelianthus annuust0
- Outcome
- damage or malfunctioning of photosynthesise0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“There were no indications that either short term (i.e. diurnal declines in Ψ leaf ) or long term (i.e. drought treatment) water deficits caused any damage or malfunctioning of photosynthesis”
t0“sunflower”
Claim · model-written summary
Prolonged drought reduced sunflower leaf area by nearly 25%.
- Taxon
- sunflowerHelianthus annuust0
- Treatment
- prolonged droughte0
- Outcome
- leaf areae0
- Direction
- decreasee0
- Value
- nearly 25%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the nearly 25% decrease in leaf area induced by prolonged drought”
t0“sunflower”
The same questions in other papers
drought · growth · Helianthus annuus (common sunflower)Results differ
49 papers in the same direction as this paper · 9 in the opposite direction
- no effect
- positive
- positive
55 papers more in this group
See all 59 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.