A closed CO2 and temperature-controlled, long-term chamber system has been developed and set up in a typical boreal forest of Scots pine (Pinus sylvestris L.) near the Mekrijärvi Research Station (62°47'N, 30°58'E, 145 m above sea level) belonging to the University of Joensuu, Finland. The main objectives of the experiment were to provide a means of assessing the medium to long-term effects of elevated atmospheric CO2 concentration (EC) and temperature (ET) on photosynthesis, respiration, growth, and biomass at the whole-tree level and to measure instantaneous whole-system CO2 exchange. The system consists of 16 chambers with individual facilities for controlling CO2 concentration, temperature, and the combination of the two. The chambers can provide a wide variety of climatic conditions that are similar to natural regimes. In this experiment the target CO2 concentration in the EC chambers was set at a fixed constant of 700 µmol mol-1 and the target air temperature in the ET chambers to track the ambient temperature but with a specified addition. Chamber performance was assessed on the base of recordings covering three consecutive years. The CO2 and temperature control in these closed chambers was in general accurate and reliable. CO2 concentration in the EC chambers was within 600-725 µmol mol-1 for 90 % of the exposure time during the "growing-season" (15 April - 15 September) and 625-725 µmol mol-1 for 88 % of the time in the "off-season" (16 September - 14 April), while temperatures in the chambers were within ±2.0 °C of the ambient or target temperature in the "growing season" and within ±3.0 °C in the "off season". There were still some significant chamber effects. Solar radiation in the chambers was reduced by 50-60 % for 82 % of the time in the "growing season" and 55-65 % for 78 % of the time in the "off season", and the relative humidity of the air was increased by 5-10 % for 72 % of the time in the "growing season" and 2-12 % for 91 % of the time in the "off season". The crown architecture and main phenophase of the trees were not modified significantly by enclosure in the chambers, but some physiological parameters changed significantly, e.g., the radiant energy-saturated photosynthesis rate, transpiration rate, maximum photochemical efficiency of photosystem 2, and chlorophyll content. and S. Kellomäki, Kai-Yun Wang, M. Lemettinen.
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). and P. Šiffel, J. Šantrůček.