Non-structural carbohydrates (NSC), mainly made-up of sugars and starch, have a versatile and important role in the physiological activity of trees. NSC dynamics is still active during the night when photosynthesis is not possible. To clarify the differences in NSC dynamics among tree species, ¹³C pulse labeling was performed in the morning and evening in pine (Pinus pinaster) and beech (Fagus sylvatica), then leaf samples were collected every few hours. The soluble carbon and starch were extracted, and the stable carbon isotope ratio of each fraction were analyzed.
In pine, 92% of the carbon fixed by photosynthesis in the morning was allocated to soluble carbon and gradually allocated to starch over time; in the evening, 67% of photosynthesis products were allocated to soluble carbon, and only 6 % was allocated to starch. In beech in the morning 60% of the carbon fixed by photosynthesis was allocated to soluble carbon and up to 17% was allocated to starch. In the evening, 30% of the photosynthetic products were allocated to soluble carbon, and 37% was allocated to starch, which was then converted from starch to sugar during the night. Large difference in NSC dynamics were found between the two species.