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| Titel |
Foliar photochemical processes and carbon metabolism under favourable and adverse winter conditions in a Mediterranean mixed forest, Catalonia (Spain) |
| VerfasserIn |
D. Sperlich, C. T. Chang, J. Peñuelas, C. Gracia, S. Sabate |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 20 ; Nr. 11, no. 20 (2014-10-16), S.5657-5674 |
| Datensatznummer |
250117641
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| Publikation (Nr.) |
 copernicus.org/bg-11-5657-2014.pdf |
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| Zusammenfassung |
| Evergreen trees in the Mediterranean region must cope with a wide range of
environmental stresses from summer drought to winter cold. The mildness of
Mediterranean winters can periodically lead to favourable environmental
conditions above the threshold for a positive carbon balance, benefitting
evergreen woody species more than deciduous ones. The comparatively lower
solar energy input in winter decreases the foliar light saturation point.
This leads to a higher susceptibility to photoinhibitory stress especially
when chilly (< 12 °C) or freezing temperatures
(< 0 °C) coincide with clear skies and relatively high
solar irradiances. Nonetheless, the advantage of evergreen species that are
able to photosynthesize all year round where a significant fraction can be
attributed to winter months, compensates for the lower carbon uptake during
spring and summer in comparison to deciduous species. We investigated the
ecophysiological behaviour of three co-occurring mature evergreen tree
species (Quercus ilex L., Pinus halepensis Mill., and
Arbutus unedo L.). Therefore, we collected twigs from the field
during a period of mild winter conditions and after a sudden cold period.
After both periods, the state of the photosynthetic machinery was tested in
the laboratory by estimating the foliar photosynthetic potential with CO2
response curves in parallel with chlorophyll fluorescence measurements. The
studied evergreen tree species benefited strongly from mild winter conditions
by exhibiting extraordinarily high photosynthetic potentials. A sudden period
of frost, however, negatively affected the photosynthetic apparatus, leading
to significant decreases in key physiological parameters such as the maximum
carboxylation velocity (Vc, max), the maximum photosynthetic
electron transport rate (Jmax), and the optimal fluorometric quantum
yield of photosystem II (Fv/Fm). The responses of
Vc, max and Jmax were highly species specific, with
Q. ilex exhibiting the highest and P. halepensis the lowest
reductions. In contrast, the optimal fluorometric quantum yield of
photosystem II (Fv/Fm) was significantly lower in
A. unedo after the cold period. The leaf position played an
important role in Q. ilex showing a stronger winter effect on sunlit
leaves in comparison to shaded leaves. Our results generally agreed with the
previous classifications of photoinhibition-tolerant (P. halepensis)
and photoinhibition-avoiding (Q. ilex) species on the basis of their
susceptibility to dynamic photoinhibition, whereas A. unedo was the
least tolerant to photoinhibition, which was chronic in this species.
Q. ilex and P. halepensis seem to follow contrasting
photoprotective strategies. However, they seemed equally successful under the
prevailing conditions exhibiting an adaptive advantage over
A. unedo. These results show that our understanding of the dynamics
of interspecific competition in Mediterranean ecosystems requires
consideration of the physiological behaviour during winter which may have
important implications for long-term carbon budgets and growth trends. |
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