Abstract
We hypothesized that photoinhibition of shade-developed leaves of deciduous hardwood saplings would limit their ability to acclimate photosynthetically to increased irradiance, and we predicted that shade-tolerant sugar maple (Acer saccharum Marsh.) would be more susceptible to photoinhibition than intermediately shade-tolerant red oak (Quercus rubra L.). After four weeks in a canopy gap, photosynthetic rates of shade-developed leaves of both species had increased in response to the increase in irradiance, although final acclimation was more complete in red oak. However, photoinhibition occurred in both species, as indicated by short-term reductions in maximum rates of net photosynthesis and the quantum yield of oxygen evolution, and longer-term reductions in the efficiency of excitation energy capture by open photosystem II (PSII) reaction centers (dark-adapted F(v)/F(m)) and the quantum yield of PSII in the light (phi(PSII)). The magnitude and duration of this decrease were greater in sugar maple than in red oak, suggesting greater susceptibility to photoinhibition in sugar maple. Photoinhibition may have resulted from photodamage, but it may also have involved sustained rates of photoprotective energy dissipation (especially in red oak). Photosynthetic acclimation also appeared to be linked to an ability to increase leaf nitrogen content. Limited photosynthetic acclimation in shade-developed sugar maple leaves may reflect a trade-off between shade-tolerance and rapid acclimation to a canopy gap.
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Claims 7
Claim · model-written summary
Photosynthetic rates rose in shade leaves of both species after canopy gap exposure.
- Treatment
- increase in irradiancee0
- Outcome
- photosynthetic rates of shade-developed leavese0
- Direction
- increasede0
- Setting
- canopy gape0
Not reportedTaxonComparator
Verbatim
e0“After four weeks in a canopy gap, photosynthetic rates of shade-developed leaves of both species had increased in response to the increase in irradiance”
Claim · model-written summary
Red oak had more complete final acclimation.
- Taxon
- red oak
_(14092717698).jpg?width=60)
Quercus rubrae0 - Outcome
- final acclimatione0
- Direction
- more completee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
_(14092717698).jpg?width=500)
Verbatim
e0“final acclimation was more complete in red oak”
Claim · model-written summary
Both species experienced short-term reductions in maximum net photosynthesis and oxygen evolution quantum yield.
- Outcome
- maximum rates of net photosynthesis and the quantum yield of oxygen evolutione0
- Direction
- reductionse0
Not reportedTaxon
Verbatim
e0“photoinhibition occurred in both species, as indicated by short-term reductions in maximum rates of net photosynthesis and the quantum yield of oxygen evolution”
Claim · model-written summary
Both species experienced longer-term reductions in PSII excitation capture and light quantum yield.
- Outcome
- efficiency of excitation energy capture by open photosystem II (PSII) reaction centers (dark-adapted F(v)/F(m)) and the quantum yield of PSII in the light (phi(PSII))e0
- Direction
- reductionse0
Not reportedTaxon
Verbatim
e0“longer-term reductions in the efficiency of excitation energy capture by open photosystem II (PSII) reaction centers (dark-adapted F(v)/F(m)) and the quantum yield of PSII in the light (phi(PSII))”
Claim · model-written summary
Photoinhibition was greater and longer in sugar maple than red oak.
- Taxon
- sugar maple
Acer saccharume0 - Outcome
- magnitude and duration of this decreasee0
- Direction
- greatere0
- Comparator
- red oake0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The magnitude and duration of this decrease were greater in sugar maple than in red oak”
Claim · model-written summary
Photosynthetic acclimation appeared linked to increased leaf nitrogen.
Not reportedTaxonDirection
Verbatim
e0“Photosynthetic acclimation also appeared to be linked to an ability to increase leaf nitrogen content”
Claim · model-written summary
Limited sugar maple acclimation may reflect a tradeoff with shade tolerance.
- Taxon
- sugar mapleAcer saccharume0
- Outcome
- Limited photosynthetic acclimatione0
- Qualifier
- trade-off between shade-tolerance and rapid acclimation to a canopy gape0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Limited photosynthetic acclimation in shade-developed sugar maple leaves may reflect a trade-off between shade-tolerance and rapid acclimation to a canopy gap”