NET PHOTOSYNTHESIS, DARK RESPIRATION AND CO2 BALANCE OF APPLE-TREES

1. Net photosynthesis and dark respiration of apple trees were measure d in a tree chamber in situ over two years. 2.The diurnal course of CO 2 exchange of a three-year-old apple tree with 5,03 m2 leaf area showe d maximum net photosynthesis of 140 mmol CO2 . tree-1 . h-1 in August and maximum dark respiration of 30 mmol CO2 . tree-1 . h-1. 3. During the annual course net photosynthesis and dark respiration peaked at 27 to 34 mol CO2 or 6.8 mol CO2 . tree-1 . month-1, between July and Sep tember. 4. Maximum carbon assimilation was 23 to 25 mol CO2 . month-1 . tree-1 in August. 5. Net photosynthesis and dark respiration of the fruiting exceeded that of the non-fruiting tree by ca. two-fold from J une to August. 6. Trunk and branches respired 0.2 to 0.6 mol CO2 . mon th-1 . tree-1 in winter.