Abstract
Periods of limited soil water availability are a feature of many temperate pasture systems and these have the potential to modify pasture plant and community responses to elevated atmospheric CO2. Using large pasture turves, previously exposed to elevated CO concentrations of 350 or 700 mmol mol−1 for 324 d2 under well-watered conditions, the morphological and physiological responses of pasture species growing at these CO2 concentrations were compared when subjected to a soil moisture deficit—and to recovery from the deficit—with those that continued to be well watered. Net leaf photosynthesis of Trifolium repens (C3 legume), Plantago lanceolata (C3) and Paspalum dilatatum (C4) was increased by exposure to elevated CO2, but there was no consistent effect of CO2 on stomatal conductance. At low soil moistures, net photosynthesis declined and stomatal conductance increased in these three species. There was a strong CO2 × water interaction in respect of net photosynthesis; in Trifolium repens, for example, elevated CO2 increased net photosynthesis by approximately 50% under well-watered conditions and this increased to over 300% when soil moisture levels reached their minimum values. Similar values were recorded for both Paspalum dilatatum and Plantago lanceolata. Potential water use efficiency (net photosynthesis/stomatal conductance) was increased by both exposure to elevated CO2 and drought. Leaf water status was measured in three species: Trifolium repens, Paspalum dilatatum and Holcus lanatus (C3). Total leaf water potential (ψt) and osmotic potential (ψπ) were decreased by drought, but CO2 concentration had no consistent effect. ψt and ψπ were highest in the C4 species Paspalum dilatatum and lowest in the legume Trifolium repens. In the wet turves, rates of leaf extension of the C3 grasses Holcus lanatus and Lolium perenne at elevated CO2 were frequently higher than those at ambient CO2, but there was no effect of CO2 concentration on the rate recorded in the C4 grass Paspalum dilatatum or the rate of leaf appearance in the legume Trifolium repens. Drought reduced leaf extension rate irrespective of CO2 in all species, but in Holcus lanatus the reduction was less severe at elevated CO2. Immediately after the dry turves were rewatered the leaf extension rates on tillers of Holcus lanatus and Lolium perenne were higher than on tillers in the wet turves, but only at ambient CO2. Consequently, despite the greater leaf extension rate during the soil moisture deficit at elevated CO2, because of the overcompensation after rewatering at ambient CO2, total leaf extension over both the drying and rewetting period did not differ between CO2 concentrations for these C3 grass species. Further investigation of this difference in response between CO2 treatments is warranted given the frequent drying and wetting cycles experienced by many temperate grasslands.
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Claims 20
Claim · model-written summary
Elevated CO2 increased net photosynthesis in three pasture species.
- Taxon
- Trifolium repens
Trifolium repense0 - Treatment
- elevated CO2e0
- Outcome
- Net leaf photosynthesise0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Net leaf photosynthesis of Trifolium repens (C3 legume), Plantago lanceolata (C3) and Paspalum dilatatum (C4) was increased by exposure to elevated CO2”
Claim · model-written summary
CO2 had no consistent effect on stomatal conductance in the three species.
- Taxon
- Trifolium repensTrifolium repense1
- Treatment
- CO2e0
- Outcome
- stomatal conductancee0
- Direction
- no consistent effecte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“but there was no consistent effect of CO2 on stomatal conductance”
e1“Net leaf photosynthesis of Trifolium repens (C3 legume), Plantago lanceolata (C3) and Paspalum dilatatum (C4) was increased by exposure to elevated CO2”
Claim · model-written summary
Low soil moisture reduced net photosynthesis in the three species.
- Taxon
- Trifolium repensTrifolium repense1
- Treatment
- low soil moisturese0
- Outcome
- net photosynthesise0
- Direction
- declinede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At low soil moistures, net photosynthesis declined”
e1“Net leaf photosynthesis of Trifolium repens (C3 legume), Plantago lanceolata (C3) and Paspalum dilatatum (C4) was increased by exposure to elevated CO2”
Claim · model-written summary
Low soil moisture increased stomatal conductance in the three species.
- Taxon
- Trifolium repensTrifolium repense1
- Treatment
- low soil moisturese0
- Outcome
- stomatal conductancee0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At low soil moistures, net photosynthesis declined and stomatal conductance increased in these three species”
e1“Net leaf photosynthesis of Trifolium repens (C3 legume), Plantago lanceolata (C3) and Paspalum dilatatum (C4) was increased by exposure to elevated CO2”
Claim · model-written summary
Elevated CO2 raised Trifolium photosynthesis by about 50% when watered.
- Taxon
- Trifolium repensTrifolium repense1
- Treatment
- elevated CO2e0
- Outcome
- net photosynthesise0
- Direction
- increasede0
- Value
- approximately 50%e0
- Qualifier
- well-watered conditionse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“elevated CO2 increased net photosynthesis by approximately 50% under well-watered conditions”
e1“Leaf water status was measured in three species: Trifolium repens, Paspalum dilatatum and Holcus lanatus (C3).”
Claim · model-written summary
Elevated CO2 raised Trifolium photosynthesis by over 300% at minimum soil moisture.
- Taxon
- Trifolium repensTrifolium repense1
- Treatment
- elevated CO2e2
- Outcome
- net photosynthesise2
- Direction
- increasede0
- Value
- over 300%e0
- Qualifier
- soil moisture levels reached their minimum valuese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“this increased to over 300% when soil moisture levels reached their minimum values”
e1“Leaf water status was measured in three species: Trifolium repens, Paspalum dilatatum and Holcus lanatus (C3).”
e2“elevated CO2 increased net photosynthesis by approximately 50%”
Claim · model-written summary
Paspalum and Plantago had similar photosynthesis responses.
- Taxon
- Paspalum dilatatum
_Paspalum_dilatatum_inflorescences.jpg?width=60)
Paspalum dilatatume0 - Outcome
- Similar valuese0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
_Paspalum_dilatatum_inflorescences.jpg?width=500)
Verbatim
e0“Similar values were recorded for both Paspalum dilatatum and Plantago lanceolata”
Claim · model-written summary
Elevated CO2 increased potential water use efficiency.
- Taxon
- Trifolium repensTrifolium repense1
- Treatment
- elevated CO2e0
- Outcome
- Potential water use efficiencye0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Potential water use efficiency (net photosynthesis/stomatal conductance) was increased by both exposure to elevated CO2 and drought”
e1“Leaf water status was measured in three species: Trifolium repens, Paspalum dilatatum and Holcus lanatus (C3).”
Claim · model-written summary
Drought increased potential water use efficiency.
- Taxon
- Trifolium repensTrifolium repense1
- Treatment
- droughte0
- Outcome
- Potential water use efficiencye0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Potential water use efficiency (net photosynthesis/stomatal conductance) was increased by both exposure to elevated CO2 and drought”
e1“Leaf water status was measured in three species: Trifolium repens, Paspalum dilatatum and Holcus lanatus (C3).”
Claim · model-written summary
Drought decreased total leaf water potential and osmotic potential.
- Taxon
- Trifolium repensTrifolium repense1
- Treatment
- droughte0
- Outcome
- Total leaf water potential (ψt) and osmotic potential (ψπ)e0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Total leaf water potential (ψt) and osmotic potential (ψπ) were decreased by drought”
e1“Leaf water status was measured in three species: Trifolium repens, Paspalum dilatatum and Holcus lanatus (C3).”
Claim · model-written summary
CO2 had no consistent effect on leaf water potentials.
- Taxon
- Trifolium repensTrifolium repense1
- Treatment
- CO2 concentratione0
- Outcome
- leaf water potentiale2
- Direction
- no consistent effecte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“but CO2 concentration had no consistent effect”
e1“Leaf water status was measured in three species: Trifolium repens, Paspalum dilatatum and Holcus lanatus (C3).”
e2“Total leaf water potential (ψt) and osmotic potential (ψπ) were decreased by drought”
Claim · model-written summary
Leaf water potentials were highest in Paspalum.
- Taxon
- Paspalum dilatatumPaspalum dilatatume0
- Outcome
- ψt and ψπe0
- Direction
- higheste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ψt and ψπ were highest in the C4 species Paspalum dilatatum and lowest in the legume Trifolium repens”
Claim · model-written summary
Leaf water potentials were lowest in Trifolium.
- Taxon
- Trifolium repensTrifolium repense0
- Outcome
- ψt and ψπe0
- Direction
- loweste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ψt and ψπ were highest in the C4 species Paspalum dilatatum and lowest in the legume Trifolium repens”
Claim · model-written summary
Elevated CO2 often increased Holcus leaf extension in wet turves.
- Taxon
- Holcus lanatus
Holcus lanatuse0 - Treatment
- elevated CO2e0
- Outcome
- rates of leaf extensione0
- Direction
- highere0
- Comparator
- ambient CO2e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“rates of leaf extension of the C3 grasses Holcus lanatus and Lolium perenne at elevated CO2 were frequently higher than those at ambient CO2”
Claim · model-written summary
Elevated CO2 often increased Lolium leaf extension in wet turves.
- Taxon
- Lolium perenne
Lolium perennee0 - Treatment
- elevated CO2e0
- Outcome
- rates of leaf extensione0
- Direction
- highere0
- Comparator
- ambient CO2e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“rates of leaf extension of the C3 grasses Holcus lanatus and Lolium perenne at elevated CO2 were frequently higher than those at ambient CO2”
Claim · model-written summary
CO2 did not affect Paspalum leaf extension or Trifolium leaf appearance.
- Taxon
- Paspalum dilatatumPaspalum dilatatume0
- Treatment
- CO2 concentratione0
- Outcome
- rate recordede0
- Direction
- no effecte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“there was no effect of CO2 concentration on the rate recorded in the C4 grass Paspalum dilatatum or the rate of leaf appearance in the legume Trifolium repens”
Claim · model-written summary
Drought reduced leaf extension in all species.
- Taxon
- Holcus lanatusHolcus lanatuse1
- Treatment
- Droughte0
- Outcome
- leaf extension ratee0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Drought reduced leaf extension rate irrespective of CO2 in all species”
e1“in Holcus lanatus the reduction was less severe at elevated CO2”
Claim · model-written summary
The drought reduction of Holcus leaf extension was less severe at elevated CO2.
- Taxon
- Holcus lanatusHolcus lanatuse0
- Treatment
- elevated CO2e0
- Outcome
- reductione0
- Direction
- less severee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“in Holcus lanatus the reduction was less severe at elevated CO2”
Claim · model-written summary
Rewatered Holcus and Lolium tillers overcompensated at ambient CO2.
- Taxon
- Holcus lanatusHolcus lanatuse0
- Outcome
- leaf extension ratese0
- Direction
- highere0
- Qualifier
- ambient CO2e0
- Comparator
- wet turvese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Immediately after the dry turves were rewatered the leaf extension rates on tillers of Holcus lanatus and Lolium perenne were higher than on tillers in the wet turves, but only at ambient CO2”
Claim · model-written summary
Total leaf extension over drying and rewetting did not differ by CO2.
- Taxon
- Holcus lanatusHolcus lanatuse1
- Treatment
- CO2 concentrationse0
- Outcome
- total leaf extensione0
- Direction
- did not differe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“total leaf extension over both the drying and rewetting period did not differ between CO2 concentrations”
e1“in Holcus lanatus the reduction was less severe at elevated CO2”
The same questions in other papers
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- no effect
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See all 8 papers →drought · physiology: water · Trifolium repens (white clover)Positive and negative results
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See all 15 papers →co2 · physiology: gas exchange · Trifolium repens (white clover)Results agree
1 paper in the same direction as this paper
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co2 · physiology: water · Trifolium repens (white clover)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.