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regular research paper |
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Acclimation of silver fir (Abies
alba Mill.) seedlings to
irradiance conditions under canopies of different tree species in Sudety Mts.
(Southern Poland) |
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Piotr Robakowski1,
Tomasz Wyka2 |
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1August
Cieszkowski Agricultural University of Poznań, Department of Forestry, Wojska
Polskiego 69, 60-625 Poznań, Poland, e-mail: pierrot@owl.au.poznan.pl (author for correspondence) 2
Adam Mickiewicz University of Poznań, Department of Biology, General Botany
Laboratory, Al. Niepodleglosci
14, 61-714 Poznań, Poland, e-mail: twyka@amu.edu.pl
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Abstract:
To determine the influence
of tree canopy composition on growth and physiological performance of silver
fir (Abies alba Mill.) in Karkonoski National Park (Sudety Mountains,
Southern Poland), three-year-old fir seedlings were planted in five forest
stands dominated by Betula pendula, Fagus sylvatica, Larix decidua, Picea
abies or Pinus sylvestris. The stands differed in canopy openness such that
young fir plants experienced drastically different light environments. After
three years of acclimation to site conditions, length of shoots, seasonal
changes in chlorophyll a fluorescence parameters, and the contents of
chlorophyll, carotenoids and nutrients in the needles were studied to
evaluate the seedling performance. Growth and photosynthetic characteristics
of the young seedlings responded strongly to local light conditions. The
lengths of leader shoot and twigs of the upper whorl reflected variation in
canopy openness during the growing season and were highest under Larix. The
potential quantum yield of photosystem II (Fv/Fm)
showed a strong depression in the spring, especially under the leafless
canopies of Betula and Fagus, probably because of the occurrence of low air
temperatures. Later in the season Fv/Fm showed
substantial recovery in all stands. Effective quantum yield ΦPSII measured under actinic light also showed a growing
trend throughout the season with the lowest levels noted in the spring,
particularly under Fagus and Betula. Fluorescence quenching revealed complex
seasonal behaviour with little obvious relationship with stand illumination,
except for consistently low value of photochemical quenching, and immediate
or high nonphotochemical quenching under the dark Picea canopy, probably
reflecting photoprotective acclimation to sunflecks. Although needle
chlorophyll content showed no relationship to ambient light, the ratio of
carotenoids to chlorophyll was positively linked to canopy openness
suggesting the existence of leaf photoprotection that evaded detection by
quenching analysis. Nutrient contents in needles depended on site conditions.
In the light-transparent Larix stand, the fir needles were strongly depleted
in Mg and Ca. Overall, however, all fir plants from experimental plots had
much lower needle nutrient content than nursery-raised plants. Needle
chlorosis found in Betula and Pinus stands was, however, not caused by
macronutrient deficiencies. Considering all variables, conditions most
conducive for fir growth and good vigor were found under larch and pine
canopies where light penetration was intermediate to high. In contrast, the
poorest conditions were found in the Betula stand, where high light
penetration in the spring was followed by shading of firs during the growing
season. |
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Key words: Abies
alba, acclimation to light, reintroduction, canopy density, pigment
content, chlorophyll fluorescence, nutrient content |