THE GROWTH AND GAS-EXCHANGE RESPONSE OF SOIL-PLANTED NORWAY SPRUCE [PICEA-ABIES (L) KARST] AND RED OAK (QUERCUS-RUBRA L) EXPOSED TO ELEVATED CO2 AND TO NATURALLY-OCCURRING DROUGHT

Norway spruce and red oak trees were planted directly into the soil an d exposed to 700 mu mol mol(-1) CO2 in open-top chambers. There were l arge inter-specific differences in response to naturally occurring dro ught during the second pear of exposure to elevated CO2. Both species had decreased assimilation rates. CO2-treated red oak had no loss of p hotosynthetic enhancement when undroughted, whereas CO2-treated Norway spruce showed a relative increase in assimilation rates only when dro ughted. The effect of CO2 on radial growth of both species was less ma rked in the second growing season, but this may have been a result of different biomass partitioning as Norway spruce shoot extension had a different pattern of growth in elevated CO2. Stomatal density and chlo rophyll content were largely unaffected by the CO2 treatment. A precis e method for measuring Norway spruce needle surface area was also deve loped.