Abstract
BACKGROUND AND AIMS: Experimental drought is well documented to induce a decline in photosynthetic capacity. However, if given time to acclimate to low water availability, the photosynthetic responses of plants to low soil moisture content may differ from those found in short-term experiments. This study aims to test whether plants acclimate to long-term water stress by modifying the functional relationships between photosynthetic traits and water stress, and whether species of contrasting habitat differ in their degree of acclimation. METHODS: Three Eucalyptus taxa from xeric and riparian habitats were compared with regard to their gas exchange responses under short- and long-term drought. Photosynthetic parameters were measured after 2 and 4 months of watering treatments, namely field capacity or partial drought. At 4 months, all plants were watered to field capacity, then watering was stopped. Further measurements were made during the subsequent 'drying-down', continuing until stomata were closed. KEY RESULTS: Two months of partial drought consistently reduced assimilation rate, stomatal sensitivity parameters (g1), apparent maximum Rubisco activity (V'(cmax)) and maximum electron transport rate (J'(max)). Eucalyptus occidentalis from the xeric habitat showed the smallest decline in V'(cmax) and J'(max); however, after 4 months, V'(cmax) and J'(max) had recovered. Species differed in their degree of V'(cmax) acclimation. Eucalyptus occidentalis showed significant acclimation of the pre-dawn leaf water potential at which the V'(cmax) and 'true' V(cmax) (accounting for mesophyll conductance) declined most steeply during drying-down. CONCLUSIONS: The findings indicate carbon loss under prolonged drought could be over-estimated without accounting for acclimation. In particular, (1) species from contrasting habitats differed in the magnitude of V'(cmax) reduction in short-term drought; (2) long-term drought allowed the possibility of acclimation, such that V'(cmax) reduction was mitigated; (3) xeric species showed a greater degree of V'(cmax) acclimation; and (4) photosynthetic acclimation involves hydraulic adjustments to reduce water loss while maintaining photosynthesis.
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Claims 9
Claim · model-written summary
Two months of partial drought reduced assimilation rate and stomatal sensitivity.
- Taxon
- Eucalyptus
.jpg?width=60)
Eucalyptust0 - Treatment
- partial droughte0
- Outcome
- assimilation rate, stomatal sensitivity parameters (g1)e0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
t0“Eucalyptusspecies”
e0“Two months of partial drought consistently reduced assimilation rate, stomatal sensitivity parameters (g1)”
Claim · model-written summary
Two months of partial drought reduced apparent maximum Rubisco activity and maximum electron transport rate.
- Taxon
- EucalyptusEucalyptust0
- Treatment
- partial droughte0
- Outcome
- apparent maximum Rubisco activity (V'(cmax)) and maximum electron transport rate (J'(max))e0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Eucalyptusspecies”
e0“Two months of partial drought consistently reduced assimilation rate, stomatal sensitivity parameters (g1), apparent maximum Rubisco activity (V'(cmax)) and maximum electron transport rate (J'(max))”
Claim · model-written summary
Eucalyptus occidentalis had the smallest decline in Vcmax and Jmax under short drought.
- Taxon
- Eucalyptus occidentalis
Eucalyptus occidentalise0 - Outcome
- V'(cmax) and J'(max)e0
- Direction
- smallest declinee0
- Setting
- xeric habitate0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus occidentalis from the xeric habitat showed the smallest decline in V'(cmax) and J'(max)”
Claim · model-written summary
After four months, Vcmax and Jmax recovered in Eucalyptus occidentalis.
- Taxon
- Eucalyptus occidentalisEucalyptus occidentalise0
- Outcome
- V'(cmax) and J'(max)e0
- Direction
- recoverede0
- Qualifier
- after 4 monthse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus occidentalis from the xeric habitat showed the smallest decline in V'(cmax) and J'(max); however, after 4 months, V'(cmax) and J'(max) had recovered”
Claim · model-written summary
Species differed in Vcmax acclimation.
- Taxon
- EucalyptusEucalyptust0
- Outcome
- V'(cmax) acclimatione0
- Direction
- differede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Eucalyptusspecies”
e0“Species differed in their degree of V'(cmax) acclimation”
Claim · model-written summary
Eucalyptus occidentalis significantly acclimated the leaf water potential threshold for steep Vcmax decline.
- Taxon
- Eucalyptus occidentalisEucalyptus occidentalise0
- Outcome
- pre-dawn leaf water potential at which the V'(cmax) and 'true' V(cmax) (accounting for mesophyll conductance) declined most steeplye0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eucalyptus occidentalis showed significant acclimation of the pre-dawn leaf water potential at which the V'(cmax) and 'true' V(cmax) (accounting for mesophyll conductance) declined most steeply during drying-down”
Claim · model-written summary
The authors infer that long drought can mitigate Vcmax reduction through acclimation.
- Taxon
- EucalyptusEucalyptust0
- Outcome
- V'(cmax) reductione0
- Direction
- mitigatede0
- Qualifier
- acclimatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Eucalyptusspecies”
e0“long-term drought allowed the possibility of acclimation, such that V'(cmax) reduction was mitigated”
Claim · model-written summary
Xeric species showed greater Vcmax acclimation.
- Taxon
- EucalyptusEucalyptust0
- Outcome
- V'(cmax) acclimatione0
- Direction
- greatere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Eucalyptusspecies”
e0“xeric species showed a greater degree of V'(cmax) acclimation”
Claim · model-written summary
The authors infer hydraulic adjustment reduces water loss while maintaining photosynthesis.
- Taxon
- EucalyptusEucalyptust0
- Outcome
- water loss while maintaining photosynthesise0
- Direction
- reducee0
- Qualifier
- hydraulic adjustmentse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Eucalyptusspecies”
e0“photosynthetic acclimation involves hydraulic adjustments to reduce water loss while maintaining photosynthesis”
The same questions in other papers
drought · physiology: photosynthesis · EucalyptusResults agree
3 papers in the same direction as this paper
- negative
- negative
- no effect
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.