MOUSSEAU, M., Université de Paris-Sud, Centre d'Orsay, Orsay, 91405, France
ENOCH, H.Z., Department of Agricultural Meteorology, Agricultural Research Organization, Volcani Center, Institute of Soils and Water, Bet Dagan, Israel

Abstract. Two‐year‐old potted sweet chestnut seedlings were grown at 350 ppm CO2 and 700 ppm, day and night in constantly ventilated tunnels during two full growing seasons, near Paris, France (48° N, 2° E). Enrichment with CO2 caused an unusual shoot growth response. After the end of July, stem elongation ceased in 62% of the CO2 enriched plants as compared with 37% in the control. The leaves of CO2‐enriched seedlings showed early senescence, indicated by premature yellowing and a decrease in chlorophyll content. This was associated with nutrient dilution brought about by the rapid growth of these trees. The increase in total dry weight of the CO2‐enriched seedlings was essentially the result of increase in the root dry weight (69%). Shoot weight decreased by 22% relative to the control. Total leaf area per enriched plant was 25% smaller than the control. This unusual pattern of growth and carbon allocation of the CO2 treated Chestnut trees emphasizes the concept of a response specificity within trees to an increase of atmospheric CO2. Copyright © 1989, Wiley Blackwell. All rights reserved