Growth responses of beech (Fagus sylvatica L.) and Norway spruce (Picea abies Karst.) to elevated atmospheric CO₂ (366 and 550 μl CO₂l⁻¹) and increased wet deposition of nitrogen (2.5 and 25 kg N ha⁻¹ a⁻¹) in combination with two soil types were studied in open-top chambers. Eight young beech and spruce trees, together with five understory species, were established in each of 32 model ecosystems. We present initial growth responses of trees during the first year of treatment which may set the trends for longer term responses to elevated CO₂. Above-ground biomass production at the system level (biometric data) during the first year and root biomass (coring data) did not show significant responses to elevated CO₂, irrespectively of other co-treatments. Increased nitrogen deposition (treatment commencing by mid-season) also had no effect on above-ground biomass, whereas end of season root biomass was significantly increased in the high-nitrogen treated low fertility acidic soil (74 g m⁻² in the high-N versus 49 g m⁻² in the low N-treatment), but not in the more fertile calcareous soil. Stem diameter increment of beech was significantly increased (+9%) under elevated CO₂ in the calcareous soil, but not in the acidic soil. The opposite was found for spruce stems, which responded positively to elevated CO₂ in the acidic soil (+11%; P<0.05) but not in the calcareous soil. These results suggest that soil type co-determines the CO₂ response of young forest trees and that these interactions are species specific. These initial differences are likely to affect long-term responses of community structure and ecosystem functioning. Soil type appears to be a key factor in predictions of forest responses to continued atmospheric CO₂ enrichment.