GROWTH AND PHOTOSYNTHESIS OF 2 DECIDUOUS FOREST SPECIES AT ELEVATED CARBON-DIOXIDE

1. Two-year-old sweet chestnut (Castanea sativa) and beech (Fagus sylvatica) seedlings were grown in large pots of forest soil, at ambient (+/-350 mul l-1) and double (700 mul l-1) atmospheric CO2 Concentration in constantly ventilated.mini-green-houses during an entire growing season. 2. CO2 enrichment caused very different changes in these two temperate deciduous species. A 20% dry weight enhancement was obtained for sweet chestnut, and a 60% enhancement in beech. This greater effect of elevated CO2 in beech was the result of a significant increase of net photosynthesis of the seedlings occurring during the whole season. However, in sweet chestnut, this increase in photosynthesis lasted only a few weeks and then an acclimation process took place. 3. No effect of increased CO2 could be found on sweet chestnut leaf area or leaf number, while a significant effect was found with beech, in which total leaf area per plant increased, owing to a greater number of growth flushes, of progressively larger leaves. 4. The partitioning of the biomass increase due to elevated CO2 was very different in the two species. All additional dry matter was allocated to the roots in sweet chestnut, while it was partitioned equally amongst all organs of the beech seedling. 5. The reactions to elevated CO2 of different tree species is discussed in relation to their specific growth strategy.