Seasonal courses of CO(2) exchange and carbon balance in fruits of Cinnamomum camphora

Carbon dioxide exchange in fruits of Cinnamomum camphora Sieb. was followed over a growing season from July to December 1992. Dark respiration was exponentially related to temperature, with a Q(10) value near 2. Light dependence of photosynthetic CO(2) refixation, i.e., the ratio of gross photosynthesis to dark respiration, was approximated by a hyperbolic function. Seasonal variation in maximum CO(2) refixation capacity ranged between 52 and 174%, reaching a maximum in early August. Daily photosynthetic CO(2) refixation ranged between 17 and 51% over the growth period. We evaluated seasonal variation in translocation rate to the fruit on the basis of the seasonal rates of gross photosynthesis, dark respiration and increase in fruit dry weight, and used the results to develop a simple carbon flow model of fruit development. Seasonal changes in translocation rate paralleled those in fruit growth rate, with two peaks during the periods before and after September. Seed formation took place in the period between the two peaks. The relationship between fruit growth rate and translocation rate was approximated by a linear function. The carbon flow model estimated that, over the reproductive period, the amount of assimilate translocated to each fruit was 377.2 mg dry weight, of which 58.5% was accounted for by weight growth and 41.5% was consumed by net respiration. Carbon dioxide refixation accounted for 22.9% of the carbon balance of the fruit.