Trees (2003) 17:211–220 DOI 10.1007/s00468-002-0226-y ORIGINAL ARTICLE Minna Vanhatalo · Jaana Bäck · Satu Huttunen Differential impacts of long-term (CO 2 ) and O 3 exposure on growth of northern conifer and deciduous tree species Received: 6 May 2002 / Accepted: 7 October 2002 / Published online: 22 November 2002  Springer-Verlag 2002 Abstract The long-term effects of elevated CO 2 and CO 2 +O 3 concentrations on the growth allocation in northern provenances of Norway spruce [Picea abies (L.) Karst.], Scots pine [Pinus sylvestris (L.)] and pubescent birch clones (Betula pubescens Ehrh.) were examined in open-top chambers after a 4-year-long experiment. The total biomass responses of the tree seedlings to increased CO 2 and CO 2 +O 3 concentrations were not statistically significant and varied between the provenances and species. The seedlings of northern origin were the least sensitive in their response to treatments. The total biomass of the Norway spruce seedlings slightly decreased in response to CO 2 in three provenances. Scots pine from the local provenance had a slight biomass increase after elevated CO 2 +O 3 treatment. The slower- growing birch clone seemed to benefit from elevated CO 2 , whereas in the faster-growing clone, reductions in biomass accumulation were seen. The combined CO 2 +O 3 treatment reduced the positive effects of elevated CO 2 , especially in the slower-growing birches. Observa- tions of significant effects were limited to a few parameters. Carbon dioxide treatment decreased needle dry weight of Norway spruce in one northern provenance. The needle and wood dry weight increased (CO 2 +O 3 ) in local Scots pine. Significant birch response was limited to increased fine root density (O 3 + CO 2 ) in the inland clone. The diverse effects of elevated CO 2 and CO 2 +O 3 on seedling growth and biomass provide evidence that exposure of northern trees to the enhanced variable CO 2 and O 3 concentrations of the future will have varied effects on the growth of these species. The direction and magnitude of those effects will differ depending on species and origins. Keywords Norway spruce (Picea abies) · Scots pine (Pinus sylvestris) · Pubescent birch (Betula pubescens)· Ozone · Carbon dioxide Introduction Responses of both coniferous and deciduous tree seed- lings to the rising concentrations of atmospheric carbon dioxide (CO 2 ) and/or ozone (O 3 ) over relatively short intervals, such as one or two growing seasons, have been widely studied (Pye 1988; Allen 1990; Saxe et al. 1998; Skärby et al. 1998; Utriainen et al. 2000). The major physiological effects of elevated CO 2 are mediated in greater relative increases in Rubisco sensitivity compared with the decreases resulting from biochemical adjust- ments (e.g. Stitt 1991; Tissue et al. 1999) and resulting in increased growth. Increasing atmospheric CO 2 concen- trations may also in the long-term stimulate the overall growth of trees through changes in their anatomy, morphology and phenology (Mousseau and Saugier 1992; Ceulemans and Mousseau 1994). Seedlings are most responsive to CO 2 during their first few weeks or months. Elevated CO 2 typically increases leaf area, leaf mass and also leaf area index (LAI) after long-term exposure (Saxe et al. 1998). However, specific leaf area is often significantly reduced by elevated CO 2 (Murray et al. 1996), indicating a change in anatomy. Ozone, however, increases leaf senescence, yet reduces stomatal conduc- tance, photosynthesis and especially the below-ground biomass accumulation (Cooley and Manning 1987; Reich 1987; Andersen 2001), and it also alters the carbohydrate and nutrient status of trees (Coleman et al. 1995; Samuelson et al. 1996). Some studies have addressed the question of whether an elevated atmospheric CO 2 can, in the long run, ameliorate the negative O 3 effects in plants, potentially through reduced stomatal conductance M. Vanhatalo · S. Huttunen ( ) ) Department of Biology/Botany, University of Oulu, P.O. Box 3000, 90014, University of Oulu, Finland e-mail: Satu.Huttunen@oulu.fi Tel.: 3588-5531527 Fax: +358-8-5531061 J. Bäck Department of Forest Ecology, University of Helsinki, P.O. Box 24, 00014, University of Helsinki, Finland