Carbon dioxide exchange, dry weight, C, and N content of `Bonita' and `Climax' blueberry (Vaccinium ashei Reade) fruit were measured from anthesis through fruit ripening to quantify developmental changes in amounts of imported C and N required for fruit development. Net photosynthesis occurred in fruit of both rabbiteye cultivars from petal fall through color break. During this time, fruit net photosynthesis declined from 16 μmol CO2/g fresh weight (FW) per hour for `Bonita' and 22 μmol CO2/g FW per hour for `Climax' to 0.2 μmol CO2/g FW per hour for both. Dark respiration for both cultivars declined following petal fall from 16 μmol CO2/g FW per hour to 3 μmol CO2/g FW per hour before increasing at fruit ripening to 9 μmol CO2/g FW per hour. Fruit C content was constant at 0.43 mg C/mg dry weight (DW) throughout development, while N content declined from 0.05 mg N/mg DW at petal fall to 0.01 mg N/mg DW at ripeness. DW accumulation and respiration accounted for 63% and 37%, respectively, of the total C requirement for fruit development. Fruit photosynthesis was estimated to contribute 15% of the total C required for fruit development in both cultivars; however, fruit photosynthesis supplied 50% of the C required during the first 10 days after bloom and 85% during the 5 days after petal fall. This large, early contribution of C from fruit photosynthesis may aid in the establishment of fruit until the current season's vegetative growth can supplement plant carbohydrate reserves in providing C for fruit development.
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