Quantitative analysis of carbon balance in the reproductive organs and leaves of Cinnamomum camphora (L.) Presl

Abstract

We investigated seasonal changes in dry mass and CO(2) exchange rate in fruit and leaves of the evergreen tree Cinnamomum camphora with the aim of quantitatively determining the translocation balance between the two organs. The fruit dry mass growth peaked in both August and October: the first increase was due to fruit pulp development and the second to seed development. Fruit respiration also increased with the rapid increase in fruit dry mass. Therefore, the carbohydrates required for fruit development showed two peaks during the reproductive period. Fruit photosynthesis was relatively high in early August, when fruit potentially re-fixed 75% of respired CO(2), indicating that fruit photosynthesis contributed 15-35% of the carbon requirement for fruit respiration. Current-year leaves completed their growth in June when fruit growth began. Current-year leaves translocated carbohydrates at a rate of approximately 10-25 mg dry weight (dw) leaf(-1) day(-1) into other organs throughout the entire fruit growth period. This rate of translocation from current-year leaves was much higher than the amount of carbohydrate required for reproduction (ca. 3 mg dw fruit(-1) day(-1)). Given the carbon balance between fruit and current-year leaves, carbohydrates for reproduction were produced within the current-year fruit-bearing shoots. C. camphora would be adaptive for steadily supplying enough amount of carbohydrate to the fruits, as there was little competition for carbohydrates between the two organs. As assimilates by leaves are used for processes such as reproduction and the formation of new shoots, photosynthesis by reproductive organs is considered to be important to compensate for reproductive cost.