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ŠUMARSKI LIST 11-12/2009 str. 11     <-- 11 -->        PDF

M. Čater, P. Simončič: PHOTOSYNTHETIC RESPONSE OF YOUNG BEECH (Fagus Sylvatica L.) ... Šumarski list br. 11–12, CXXXIII (2009), 569-576

In the Kočevski Rog area, differences among the tree ged one (at Snezna jama).Assimilation rates were higlight
categories are smaller in the virgin forest where no hest in all categories in virgin forests, despite the comdifferences
in response between canopy and edge were parable amount of nitrogen in leaves on the two plots.
confirmed (Post hoc LSD, p=0.0969) than in the mana-


Sensitivity of photosynthesis is similar for all C


plants and is in proportion with mesophyll CO concen


tration (Farquhar etal. 1980). Many studies indicate
that trees have higher mesophyll resistance for CO,


consequently lower photosynthesis and are therefore
more susceptible to the increase of atmospheric CO


concentration. In the view of climatic changes numerous
and often contradictory conclusions are being presented
about the response of plants and future development of
tree adaptation to environmental changes, especially due
to temperature increase (Körner, 2006), decrease in
amount of precipitation and changes in water supply
(Davies 2006) and increase of atmospheric CO con


centration (Ziska andBunce2006).
Light, nutrients, water and CO are abiotic parame


ters, necessary for the plant growth. Efficiency and
photosynthetic regulation are governed by ribulose-1,5
biphosphat carboxylase (rubisco), which is genetically
defined (Cheng etal. 1998). In general, by higher atmospheric
CO; protein synthesis in leaves increases,


stomatal aperture decreases, water use-efficiency and
C/N relation on the leaf level are increased, while on
the whole plant level growth is stimulated (Kimball
1993, Ghannoum et al. 2000).

By the increased amount of CO photosynthesis per


unit of the leaf area would increase, which is dependent
on the nitrogen supply. Respiration and root activities
would also increase, while biomass would be allocated
into roots (sweet chestnut) or increased proportionally
over whole plant (beech), which indicates a species-
specific response (Kohen etal. 1993).

In spite of relatively good insight into processes of
carbon dynamics on the leaf level in changed CO en


vironment it is difficult to make a prognosis of future
response of the whole plant also because of a short-
time interval of observations and numerous possible interactions
that haven’t been recognized yet (Increased
WUE might stimulate development of foliar fungi
(Thompson andDrake1994) while more sugars in
assimilation apparatus might stimulate the development
of pathogens and infections (Hibberd et al.
1996) etc.). Recent research quote up to 30 % increase
of growth in ambient with two times higher CO envi


ronment (Medylin etal. 2001).Asmaller probability
that such increase would reflect in long term growth in

assimilation was confirmed by Batič 2007, where

growth only increased at the beginning, and was later

reduced in time. Our analysis conirmed the differences
in response between beech under shelter, at the forest
edge and in the open. In spite of these differences, the
highest assimilation rates were measured on the research
plots of Pohorje complex and lowest on the
plots of Kočevski Rog. Results also indicate a different
response of young beech between managed forest
(Snežna jama) and virgin forest (Rajhenav); differences
between light categories were more pronounced
in the managed forest, while in virgin forest response to
same light conditions was more intense than in managed
forest. Photosynthetic yield in all categories was
higher in virgin forest. Light compensation point was
higher on plots of Pohorje complex compared to plots
in Kočevski Rog (data not shown).

Water use efficiency (WUE) was in all cases highest
under shelter and lowest in open conditions, similar to
photosynthetic nitrogen use-efficiency (PNUE).

Self shading and nitrogen redistribution within
whole plant could potentially underlie the degree of
photosynthetic acclimation to elevated CO (Takeu


chi et al. 2001); it is clear that interactions with other
potential environmental variables (light, nutrients) will
determine the regulation of carbon sources and sinks at
the leaf level (Lewis etal. 2002), but the ability to utilize
the knowledge and predict a whole plant response is
still limited and subject of controversy (Poorter 1998,

There were no significant differences in the content
of leaf nitrogen between plots. Leaf nitrogen values
were on all plots (expressed in units per leaf area) highest
in open conditions, without shading. Response of
young beech to different CO concentrations was simi


lar to response of young beech to different light intensity;
differences between managed and virgin forest
were even bigger under canopy and edge conditions.

In Kočevski Rog young beech is more shade tolerant,
relative response to increased light intensity and different
CO concentration is higher than response of young


beech in Pohorje within same light intensities. Responses
in managed and virgin forest are different: in the virgin
forest young beech trees are more shade-tolerant,
reaction of different light categories to elevated CO
concentration is similar and more homogenous, compared
to managed forest where differences between cate

gories are more pronounced. Kočevje region (Snežna

jama and Rajhenav) is well known for its forest manage