[Distribution characteristics of delta13C values in different organs of Abies georgei growing at alpine timberline].

Based on the analysis of the distribution characteristics of delta13C values in the needle, twig, branch, trunk, and root of different age Abies georgei growing at the timberline of Sergyemla Mountain on the southeast edge of Tibetan Plateau, this paper studied the process or extent of post-photosynthetic delta13C fractionation and its affecting factors. The results showed that the organ-specific difference in delta13C values was highly significant (P < 0.001), with the sequence of trunk (-24.19 per thousand +/- 0.34 per thousand) > branch (-24.56 per thousand +/- 0.62 per thousand) > root (-25.05 per thousand +/- 1.08 per thousand) > twig (-25.12 per thousand +/- 0.54 per thousand) > needle (-7.25 per thousand +/- 0.63 per thousand), which suggested that an obvious post-photosynthetic delta13C fractionation was existed between photosynthetic and non-photosynthetic organs. With increasing age of needle and twig, the delta13C value in needle decreased significantly, while that in twig showed a reverse pattern (P < 0.01). The delta13C value in needle increased significantly (P < 0.01) from lower canopy to higher canopy, whereas no significant difference (P > 0.05) of delta13C value in twig was observed among different canopy heights. A significant vertical gradient of delta13C value existed in the branches at a distance of 2.5 m from trunk (P < 0.01), but disappeared at a distance of 1.5 m or 0.5 m. At the same canopy height, the delta13C value in twig decreased with increasing distance from trunk, which was most obvious in the twigs of middle and lower canopies. All of these suggested that post-photosynthetic delta13C fractionation occurred in alpine A. georgei, and the carbon need for the growth of height-specific tree stems or branches was not wholly supplied by the corresponding segment of the tree crown at the same height.