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Influences of atmospheric CO 2 enrichment on the responses of sugar maple and trembling aspen to defoliation
Author(s) -
KRUGER ERIC L.,
VOLIN JOHN C.,
LINDROTH RICHARD L.
Publication year - 1998
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1046/j.1469-8137.1998.00249.x
Subject(s) - photosynthesis , sugar , maple , acclimatization , specific leaf area , relative growth rate , carbon dioxide , salicaceae , aceraceae , botany , biology , horticulture , chemistry , woody plant , growth rate , ecology , biochemistry , geometry , mathematics
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.