Abstract: Stable carbon isotope composition can accurately indicate ecosystem carbon cycling and provide key information for the study of the influence of forest succession on the carbon cycling and carbon sequestration potential. We measured the δ¹³C values and carbon and nitrogen contents of leaf, trunk, root, litter, and soil along a forest successional gradient in Changbai Mountain, which included a middle-aged poplar-birch secondary forest, a mature poplar-birch secondary forest, and an old-growth broad-leaved Korean pine forest. The results showed that leaf δ¹³C reduced with their position from the upper canopy to lower canopy, bark δ¹³C was less than xylem, fine root δ¹³C was less than course root. In contrast to the secondary forests, δ¹³C of the undecomposed litter layer was less than that of the semi-decomposed layer and decomposed litter layer in the broad-leaved Korean pine forest. Soil δ¹³C increased with depth. The ascending order of mean δ¹³C was leaf, litter, root, trunk, and soil, indicating that there is obvious fractionation among different organs of plants and among different parts of a specific organ. In addition, plant δ¹³C first decreased and then increased with the succession process, but soil δ¹³C increased with the succession processes. The different patterns of the changes of plant and soil δ¹³C along forest succession could be explained by the relationship between nitrogen content and carbon isotope fractionation effect, indicating that carbon isotope fractionation was affected by the change of dominant tree species and the variation of carbon turnover rate.

Key words: carbon cycle, succession, carbon isotope, Changbai Mountain, temperate forest.