Carbon dioxide enrichment reduces shoot growth in sweet chestnut seedlings (<i>Castanea sativa</i> Mill.)^*

Abstract

Abstract. Two‐year‐old potted sweet chestnut seedlings were grown at 350 ppm CO 2 and 700 ppm, day and night in constantly ventilated tunnels during two full growing seasons, near Paris, France (48° N, 2° E). Enrichment with CO 2 caused an unusual shoot growth response. After the end of July, stem elongation ceased in 62% of the CO 2 enriched plants as compared with 37% in the control. The leaves of CO 2 ‐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 CO 2 ‐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 CO 2 treated Chestnut trees emphasizes the concept of a response specificity within trees to an increase of atmospheric CO 2 .