Articles by Kaisa Laitinen

The effects of realistically elevated O₃ and CO₂ concentrations on the needle ultrastructure and photosynthesis of ca. 20-year-old Scots pine (Pinus sylvestris L.) saplings were studied during one growth period in open-top field chambers situated on a natural pine heath at Mekrijärvi, in eastern Finland. The experiment included six different treatments: chamberless control, filtered air, ambient air and elevated O₃, CO₂ and O₃ + CO₂. Significant increases in the size of chloroplast and starch grains were recorded in the current-year needles of the saplings exposed to elevated CO₂ These responses were especially clear in the saplings exposed to elevated O₃ + CO₂ concentrations. These treatments also delayed the winter hardening process in cells. In the shoots treated with O₃, CO₂ and combined O₃ + CO₂ the P_max was decreased on average by 50% (ambient CO₂) and 40% (700 ppm CO₂). Photosynthetic efficiency was decreased by 60% in all the treated shoots measured under ambient condition and by 30% in the CO₂ and O₃ + CO₂ treated shoots under 700 ppm. The effect of all the treatments on photosynthesis was depressive which was probably related to evident accumulation of starch in the chloroplasts of the pines treated with CO₂ and combined O₃ + CO₂. But in O₃ treated pines, which did not accumulate starch in comparison to pines subjected to ambient air conditions, some injuries may be already present in the photosynthetic machinery.

• Palomäki, E-mail: vp@mm.unknown
• Holopainen, E-mail: th@mm.unknown
• Kellomäki, E-mail: sk@mm.unknown
• Laitinen, E-mail: kl@mm.unknown

According to a recently presented hypothesis, the predicted climatic warming will cause height growth onset of trees during mild spells in winter and heavy frost damage during subsequent periods of frost in northern conditions. The hypothesis was based on computer simulations involving a model employing air temperature as the only environmental factor influencing height growth onset. In the present study, the model was tested in the case of eastern Finnish Scots pine (Pinus sylvestris L.) saplings. Four experimental saplings growing on their natural site were surrounded by transparent chambers in autumn 1990. The air temperature in the chambers was raised during the winter to present an extremely warm winter under the predicted conditions of a double level of atmospheric carbon dioxide. The temperature treatment hastened height growth onset by two months as compared to the control saplings, but not as much as expected on the basis of the previous simulation study. This finding suggests that 1) the model used in the simulation study needs to be developed further, either by modifying the modelled effect of air temperature or by introducing other environmental factors, and 2) the predicted climatic warming will not increase the risk of frost damage in trees as much as suggested by the previous simulation study.

The PDF includes an abstract in Finnish.

• Hänninen, E-mail: hh@mm.unknown
• Kellomäki, E-mail: sk@mm.unknown
• Laitinen, E-mail: kl@mm.unknown
• Pajari, E-mail: bp@mm.unknown
• Repo, E-mail: tr@mm.unknown