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
1995
Dixon, Martin | THIEC, DIDIER LE | Garrec, Jean-Pierre
Norway spruce and red oak trees were planted directly into the soil and exposed to 700 μmol mol‐¹ CO₂ in open‐top chambers. There were large inter‐specific differences in response to naturally occurring drought during the second year of exposure to elevated CO₂. Both species had decreased assimilation rates. CO₂‐treated red oak had no loss of photosynthetic enhancement when undroughted, whereas CO₂‐treated Norway spruce showed a relative increase in assimilation rates only when draughted. The effect of CO₂ on radial growth of both species was less marked 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 chlorophyll content were largely unaffected by the CO₂ treatment. A precise method for measuring Norway spruce needle surface area was also developed.
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