Diurnal course of photochemical activity of winter-adapted Scots pine at subzero temperatures |
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Authors: | P?Siffel Email author" target="_blank">J?SantrucekEmail author |
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Institution: | (1) Institute of Plant Molecular Biology, Academy of Sciences of the Czech Republic, Branisovska 31, 370 05 Ceske Budejovice, Czech Republic;(2) Institute of Physical Biology, University of South Bohemia, Zamek 136, 373 33 Nove Hrady, Czech Republic;(3) Faculty of Biology, Department of Plant Physiology, University of South Bohemia, Branisovska 31, 370 05 Ceske Budejovice, Czech Republic |
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Abstract: | The photochemical activity of native Central Siberian Scots pine trees (Pinus sylvestris L) was estimated from the middle of February to the middle of March 2001. We measured chlorophyll (Chl) fluorescence in attached
intact needles from trees located approx. 30 km west of the Yenisey river (60°44′N, 89°09′E) near the village of Zotino. In
this period, the air temperature varied between ?39 °C and +7 °C. At temperatures below ?10 °C, P. sylvestris needles did not exhibit any variable Chl fluorescence during the daylight period. During the night, however, the effective
quantum yield of photosystem 2 (PS2) photochemistry, Φ2 Φ2 = (Fm′ ? Ft)/Fm′), increased from values near zero to values between 0.05 and 0.20 depending on the needle temperature and sample investigated.
The increase started soon after dusk and lasted for 3–6 h depending on the temperature. A faster increase of Φ2 was found for temperatures around ?16 °C, and lower rates occurred at lower temperatures. Irrespective of the temperature,
Φ2 decreased rapidly to near zero values at dawn, when the photosynthetic photon flux density increased to about 1–5 μmol m?2 s?1, and remained near zero throughout the day. At temperatures higher than ?10 °C, the diurnal decrease and the nocturnal increase
of Φ2 were less distinct or disappeared completely. Hence the winter-adapted Scots pine maintains some photochemical activity of
PS2 even at extremely cold temperatures. The capacity of photochemical reactions below ?10 °C is, however, very limited and
PS2 photochemistry is saturated by an extremely low irradiance (less than 5 μmol m?2 s?1). |
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Keywords: | chlorophyll fluorescence cold adaptation diurnal changes photosystem 2 Pinus sylvestris L quantum yield |
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