GROWTH-RESPONSES TO ELEVATED CO2 AND SOIL QUALITY IN BEECH-SPRUCE MODEL-ECOSYSTEMS

Growth responses of beech (Fagus sylvatica L.) and Norway spruce (Pice a abies Karst.) to elevated atmospheric CO2 (366 and 550 mu l CO2 l(-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 chamb ers. 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 w hich may set the trends for longer term responses to elevated CO2. Abo ve-ground biomass production at the system level (biometric data) duri ng the first year and root biomass (coring data) did not show signific ant responses to elevated CO2, irrespectively of other cc-treatments. Increased nitrogen deposition (treatment commencing by mid-season) als o had no effect on above-ground biomass, whereas end of season root bi omass was significantly increased in the high-nitrogen treated low fer tility 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 d iameter increment of beech was significantly increased (+9%) under ele vated CO, in the calcareous soil, but not in the acidic soil. The oppo site was found for spruce stems, which responded positively to elevate d CO2 in the acidic soil (+ 11%; P < 0.05) but nor in the calcareous s oil. These results suggest that soil type co-determines the CO2 respon se of young forest trees and that these interactions are species speci fic. These initial differences are likely to affect long-term response s of community structure and ecosystem functioning. Soil type appears to be a key factor in predictions of forest responses to continued atm ospheric CO2 enrichment.