Finnish Forest Research Institute  Metla

Media release 23.05.2005

Climate change has an impact on conifer needles and growth

As a result of human activities the carbon dioxide level of the atmosphere is rising, leading to an increase in the average global surface air temperature. Ambient carbon dioxide level restricts the photosynthesis of the plants. The elevation of the carbon dioxide level is predicted to increase the growth. The ability of the conifer to bind the carbon dioxide in the assimilation is important to the forest yield. It is also important as a factor to slow down the progress of the climate change. Acclimation of conifer needles in the future climate was studied in the doctoral thesis for the University of Kuopio by Ms. Eeva Luomala´s “ Photosynthesis, chemical composition and anatomy of Scots pine and Norway spruce needles under elevated atmospheric CO2 concentration and temperature.”

The temperatures during the growing period are often low in the northern coniferous forest zone. Therefore the raise of the temperature can be assumed to increase the growth of the trees. However, there are often changes in leaves when trees acclimate to the elevated carbon dioxide level. Therefore the increase in the growth might stay minor than expected. The deficiency of the nutrients can deepen these changes and decrease the benefit of the elevated carbon dioxide level for trees. On the other hand the rise of the temperature speeds decomposition of litter and increases the availability of the nutrients. There is very little experimental information about the joint effects of elevated carbon dioxide and the temperature to conifers.

In this doctoral thesis research the effect of the elevated carbon dioxide level and the temperature to the physiology and growth of the pine and the spruce was examined. At the Mekrijärvi Research Station of the University of Joensuu 25-30 year old pines were enclosed in the transparent chambers whose carbon dioxide level and temperature were elevated. In the other experiment at the Mekrijärvi Research Station done by branch bag technology was examined the importance of the nitrogen availability when the carbon dioxide was elevated. In the test conducted in the growth chambers of Kuopio University the 1-2 year old container saplings were grown in the elevated carbon dioxide level and temperature. In the tests the carbon dioxide level of the air and the temperature were elevated to the level which was estimated to be dominant in the end of this century in Finland. In all tests the photosynthetic characteristics of branches were studied and the needle samples were gathered for the laboratory research, which was conducted in Metla's research station in Suonenjoki.

The young pine trees grown in the elevated carbon dioxide level showed often a reduction in the assimilation capacity of the needles. Mostly this was caused by the decrease in the amount of Rubisco enzyme functioning in carbon binding and was in connection with the fall of the nitrogen concentration of the needles. Sometimes the elevated temperature compensated the reductions of Rubisco amount and the nitrogen concentration. The nitrogen fertilizer alone did not have much effect on the photosynthetic machinery of the pine needles, but the nitrogen fertilizer compensated the decrease caused by the carbon dioxide in the amounts of the assimilation components, as did also the elevated temperature. Opposition to the expectations, the carbon dioxide did not have much effect on the anatomy of the pine needles whereas in the elevated temperature the stomatal density of the needles was smaller and they were thinner than those grown in the ambient temperature. The carbon dioxide did not hardly affect the characteristics or the functions of the needles of the spruce or pine saplings, whereas the raised temperature lead to the decrease of the assimilation components. The elevated temperature alone increased the growth of the saplings and the increase of the growth was biggest when both the carbon dioxide level and the temperature were elevated.

The results show that in spite of the changes in the needles, increased growth of the pine and the spruce is highly probable in the future climate. However, the sufficient nutrients of the soil are critical for the acclimation and the growth of the needles. The research also indicated that the changes in the structure and the function of the needles varied a lot from year to another. In addition, the acclimation of the seedlings differed from the acclimation of the young trees which shows that it is difficult to generalize the received results from short-term exposures of the young trees to the comparable results of almost the timber forest.

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