Abstract
Impacts of defoliation on the growth and physiology of sugar maple ( Acer saccharum Marsh.) and trembling aspen ( Populus tremuloides Michx.) were examined in ambient and CO 2 ‐enriched atmospheres. Saplings were grown for 70 d in controlled environments, wherein CO 2 mole fractions averaged either 356 μmol mol −1 or 645 μmol mol −1 , under a PPF of 500 μmol m −2 s −1 . On day 49 of the study, 50% of the leaf area was removed from a subset of each species in both CO 2 environments. Relative growth rate ( rgr ) and its physiological and morphological determinants were monitored before and after defoliation. For non‐defoliated saplings of both species, a slight stimulation of rgr ( c . 5%) in elevated CO 2 led to a modest increase (9–11%) in final sapling weight. In the case of maple, the minimal growth response corresponded with minor CO 2 effects on specific leaf area ( sla ) and leaf weight ratio ( lwr ), and an apparent CO 2 ‐induced down‐regulation of photosynthetic metabolism. For aspen, the CO 2 stimulation of photosynthesis was largely offset by a decrease in sla . Responses to defoliation differed markedly between species and CO 2 environments. Defoliation decreased maple rgr in ambient CO 2 , whereas the opposite occurred in elevated CO 2 . The latter led to complete recovery of plant weight (compensation), and was attributed to a defoliation‐induced increase in carbon allocation to new leaves, along with a reversal of photosynthetic CO 2 acclimation in that foliage. In both environments, aspen rgr increased after defoliation, facilitating almost full compensation. Defoliation increased light penetration into the aspen canopy, and it was estimated that the resultant stimulation of photosynthesis in lower leaves would have more than offset the concomitant decrease in lwr . CO 2 enrichment might substantially enhance the ability of certain tree species to recover from herbivory. Moreover, responses to elevated CO 2 might be largest in the presence of stresses, such as herbivory, that decrease plant source∶sink ratios.
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Claims 14
Claim · model-written summary
Elevated CO2 slightly stimulated relative growth rate in nondefoliated maple and aspen.
- Taxon
- sugar maple and trembling aspent0
- Treatment
- elevated CO 2e0
- Outcome
- rgre0
- Direction
- stimulatione0
- Value
- c . 5%e0
Not reportedComparator
Verbatim
e0“For non‐defoliated saplings of both species, a slight stimulation of rgr ( c . 5%) in elevated CO 2”
t0“sugar maple and trembling aspen”
Claim · model-written summary
Elevated CO2 increased final sapling weight in both species.
- Taxon
- sugar maple and trembling aspent0
- Treatment
- CO2 enrichmentt1
- Outcome
- final sapling weighte0
- Direction
- increasee0
- Value
- 9–11%e0
Not reportedComparator
Verbatim
e0“a modest increase (9–11%) in final sapling weight”
t0“sugar maple and trembling aspen”
t1“CO2 enrichment”
Claim · model-written summary
Maple showed minor CO2 effects on specific leaf area and leaf weight ratio.
- Taxon
- sugar maple
Acer saccharumt0 - Outcome
- specific leaf area ( sla ) and leaf weight ratio ( lwr )e0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“minor CO 2 effects on specific leaf area ( sla ) and leaf weight ratio ( lwr )”
t0“sugar maple”
Claim · model-written summary
Maple showed apparent CO2 induced down regulation of photosynthetic metabolism.
- Taxon
- sugar mapleAcer saccharumt0
- Treatment
- CO 2e0
- Outcome
- photosynthetic metabolisme0
- Direction
- down‐regulatione0
- Qualifier
- apparente0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“an apparent CO 2 ‐induced down‐regulation of photosynthetic metabolism”
t0“sugar maple”
Claim · model-written summary
Aspen photosynthesis was stimulated by CO2.
Not reportedComparator
Verbatim
e0“For aspen, the CO 2 stimulation of photosynthesis”
t0“trembling aspen”
Claim · model-written summary
Aspen specific leaf area decreased under CO2.
Not reportedComparator
Verbatim
e0“the CO 2 stimulation of photosynthesis was largely offset by a decrease in sla”
t0“trembling aspen”
Claim · model-written summary
Defoliation decreased maple relative growth rate under ambient CO2.
- Taxon
- sugar mapleAcer saccharumt0
- Treatment
- Defoliatione0
- Outcome
- rgre0
- Direction
- decreasede0
- Qualifier
- ambient CO 2e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Defoliation decreased maple rgr in ambient CO 2”
t0“sugar maple”
Claim · model-written summary
Defoliation increased maple relative growth rate under elevated CO2.
- Taxon
- sugar mapleAcer saccharumt0
- Treatment
- Defoliatione0
- Outcome
- rgre0
- Direction
- increaseinferrede0
- Qualifier
- elevated CO 2e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Defoliation decreased maple rgr in ambient CO 2 , whereas the opposite occurred in elevated CO 2”
t0“sugar maple”
Claim · model-written summary
Defoliated maple fully recovered plant weight under elevated CO2.
- Taxon
- sugar mapleAcer saccharumt0
- Outcome
- complete recovery of plant weighte0
- Direction
- recoverye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The latter led to complete recovery of plant weight (compensation)”
t0“sugar maple”
Claim · model-written summary
Maple defoliation increased allocation of carbon to new leaves.
- Taxon
- sugar mapleAcer saccharumt0
- Treatment
- defoliatione0
- Outcome
- carbon allocation to new leavese0
- Direction
- increasee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a defoliation‐induced increase in carbon allocation to new leaves”
t0“sugar maple”
Claim · model-written summary
Maple defoliation reversed photosynthetic CO2 acclimation in new foliage.
- Taxon
- sugar mapleAcer saccharumt0
- Treatment
- defoliatione1
- Outcome
- photosynthetic CO 2 acclimatione0
- Direction
- reversale0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a reversal of photosynthetic CO 2 acclimation in that foliage”
e1“defoliation‐induced increase in carbon allocation to new leaves”
t0“sugar maple”
Claim · model-written summary
Aspen relative growth rate increased after defoliation in both CO2 environments.
- Taxon
- trembling aspent0
- Treatment
- defoliatione0
- Outcome
- rgre0
- Direction
- increasede0
- Qualifier
- both environmentse0
Not reportedComparator
Verbatim
e0“In both environments, aspen rgr increased after defoliation”
t0“trembling aspen”
Claim · model-written summary
Aspen almost fully compensated weight after defoliation.
Verbatim
e0“facilitating almost full compensation”
t0“trembling aspen”
Claim · model-written summary
Defoliation increased light penetration into the aspen canopy.
- Taxon
- trembling aspent0
- Treatment
- Defoliatione0
- Outcome
- light penetration into the aspen canopye0
- Direction
- increasede0
Not reportedComparator
Verbatim
e0“Defoliation increased light penetration into the aspen canopy”
t0“trembling aspen”
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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.