To investigate the ozone-influence on the carbon (C) allocation of adult beech and spruce trees a ¹² C-tracer experiment was performed in summer (August/September) 2006 at Kranzberg Forest. The SFB partner group B2 (Menzel/Werner) has installed a ¹²CO₂ fumigation system in the canopies of 12 beech and spruce trees (Fig 1) . This allowed the application of ¹² C labelled CO ₂ (d ¹³ C of c. -47 ‰ ) in the ambient air in the canopy. To this end the CO ₂ concentration was increased on average by about 100 ppm, resulting in a changed in d ¹³ C of the air from c. -9 ‰ to -17 ‰ during the 18 days of labelling. The uptake of the ¹² CO ₂label could be documented by measurements d ¹³ C of coarse root respiration, which was assessed via a closed gas exchange system. 5 days after the label was applied, Keeling plot analysis showed a declining d ¹³ C of respiratory CO ₂ from initially c. -28 down to -31‰.

Fig. 1: Fumigation tubes installed in the sun and shade crown of adult beech and spruce trees at Kranzberg Forest. The ¹² CO ₂ label was applied for a period of 18 days in summer 2006.