Sixteen open-top chambers (divided into two halves each containing eit
her calcareous or acidic soil) were supplied in four combinations with
either 366 or 550 mu l CO2 L-1, and either 2.5 or 25 kg N ha-(1) y(-1
) (ammonium nitrate by irrigation). The development of young spruce (P
icea abies) and beech (Fagus sylvatica) trees planted in the chambers
together with understory plants will be studied over four years. The p
resented data are preliminary results from the first year of this expe
riment and refer to 64 spruce and 64 beech trees from two different Sw
iss spruce and beech provenances; two trees each per soil type, sample
d in July and September in each chamber. Specific current-year spruce
nee die length (length/dry mass) was reduced by elevated CO2 due to an
increase in dry mass. Beech specific leaf area was only temporarily r
educed in July. Elevated CO2 induced an earlier autumnal leaf discolor
ation. 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 beec
h, may therefore profit from elevated CO2 (when other resources are un
limited) by increasing shoot and needle dry mass.