Poster: Global Change

Abs # 63: Growth and photosynthesis of two silver birch clones exposed to elevated CO2 and O3: three- year field experiment

Presenter:	Riikonen, Johanna , johanna.riikonen@uku.fi
Authors	Riikonen, Johanna  (A) (B)  Holopainen, Toini  (A)   Oksanen, Elina  (A)   Vapaavuori, Elina  (B)
Affiliations:	(A): University of Kuopio, Department of Ecology and Environmental Sciences (B): Finnish Forest Research Institute, Suonenjoki Research Station

Two clones of 8-year-old silver birch (Betula pendula Roth) were exposed to elevated CO2 and O3 concentrations during 1999-2001, using open top chambers in the field. The treatments were: outside control, chamber control, 2* ambient CO2, 2* ambient O3, and 2* ambient CO2 + 2* ambient O3, as 4 replicates. Growth, photosynthesis and biochemical properties of clones 4 and 80 were studied. The aims of the study were to examine: whether silver birch benefits from increasing CO2 in the atmosphere, whether elevated O3 causes damage and growth losses and whether CO2 can compensate for the negative effects of O3 if such losses exist. The clones responded differently to the treatments. Growth of clone 80 increased in elevated CO2 but was only slightly affected by elevated O3. In clone 4 growth of was reduced in elevated O3, and the response to elevated CO2 was small. The negative effect of O3 was caused by reduced leaf area and root growth and by accelerated leaf abscission. Elevated CO2 protected the trees from negative effects of O3. Although growth of clone 80 was more responsive to elevated CO2 than in clone 4, net photosynthesis, measured at growth CO2 concentration, was increased by treatments with elevated CO2 only by 23 % in clone 80, while in clone 4 the increase was 43 %. When measured at 360 ppm CO2 both elevated CO2 and CO2 + O3 decreased net photosynthesis by 16 % and 19 %, in clones 4 and 80, respectively. The downregulation of photosynthesis was related to decreased activity and content of Rubisco, reduced N concentration and increased C:N ratio and accumulation of starch in the leaves. Elevated O3 had no clear effect on photosynthesis or on biochemistry of the leaves and the effect of elevated CO2 + O3 was similar to that of elevated CO2 alone.