Leaf expansion, population dynamics and reproduction under elevated CO
2 were studied for two dominant and four subdominant species in a high
alpine grassland (2500 above sea level, Swiss Central Alps). Plots of
alpine heath were exposed to 335 mu l l(-1) and 680 mu l l(-1) CO2 in
open-top chambers over three growing seasons. Treatments also include
d natural and moderately improved mineral nutrient supply (40 kg N ha(
-1) year(-1) in an NPK fertilizer mix). Seasonal dynamics of leaf expa
nsion, which was studied for the dominant graminoid Carer curvula only
, were not affected by elevated CO2 during two warm seasons or during
a cool season. Improved nutrient supply increased both the expansion r
ate and the duration of leaf growth but elevated CO2 did not cause any
further stimulation. Plant and tiller density (studied in all species
) increased under elevated CO2 in the codominant Leontodon helveticus
and the subdominant Trifolium alpinum, remained unchanged in two other
minor species Poa alpina and Phyteuma globulariifolium, and decreased
in Carex curvula. In Potentilla aurea elevated CO2 compensated for a
natural decline in shoot number. By year 3 the number of fertile shoot
s in Leontodon and individual seed weight in Carex were slightly incre
ased under elevated CO2, indicating CO2 effects on sexual reproduction
in these two dominant species. The results suggest that the effects o
f elevated CO2 on the population dynamics of the species studied were
not general, but species-specific and rather moderate effects. However
, the reduction of tiller density in Carex curvula, in contrast to the
increases observed in Leontodon helveticus and Trifolium alpinum, ind
icates that elevated CO2 may negatively affect the abundance of the sp
ecies most characteristic of this alpine plant community.