Sixteen open-top chambers (divided into two halves each containing either calcareous or acidic soil) were supplied in four combinations with either 366 or 550 μl CO₂ L⁻¹, and either 2.5 or 25 kg N ha⁻¹ y⁻¹) (ammonium nitrate by irrigation). The development of young spruce (Picea abies) and beech (Fagus sylvatica) trees planted in the chambers together with understory plants will be studied over four years. The presented data are preliminary results from the first year of this experiment and refer to 64 spruce and 64 beech trees from two different Swiss spruce and beech provenances; two trees each per soil type, sampled in July and September in each chamber. Specific current-year spruce needle length (length/dry mass) was reduced by elevated CO₂ due to an increase in dry mass. Beech specific leaf area was only temporarily reduced in July. Elevated CO₂ induced an earlier autumnal leaf discoloration. Total current-year shoot length per spruce and total number of leaves per beech tree were not influenced by the first year treatment with elevated CO₂. N deposition had no effect on these parameters, but soil type influenced spruce needle colour. Spruce, in contrast to beech, may therefore profit from elevated CO₂ (when other resources are unlimited) by increasing shoot and needle dry mass.