中文摘要：

通过分析青藏高原东南部色季拉山林线物种急尖长苞冷杉不同年龄叶片、嫩枝、枝条、树干及根系的稳定碳同位素比值（6BC）及其空间分布特征，研究了植物光合作用后稳定碳同位素分馏及其影响因素．结果表明：植物不同器官δ^13C值差异显著（P〈0．001），为树干（-24．19‰）〉枝条（-24．56‰）〉根部（-25．05‰）〉嫩枝（-25．12‰）〉叶片（-27．25‰），说明从光合作用器官到非光合作用器官有明显的碳同位素分馏，且非光合作用器官之间也存在差异．随着急尖长苞冷杉叶片或嫩枝年龄的增加，叶片δ^13C值降低，而嫩枝δ^13C值升高（P〈0．01）．冠层上部叶片δ^13C值明显高于冠层下部（P〈0．01），嫩枝δ^13C值则无显著性差异（P〉0．05）．远离树干2．5m的枝条δ^13C值有明显的高度变化（P〈0．01），而离树干较近（1．5或0．5m）的枝条及树干在不同高度之间无差异（P〉0．05）．在同一冠层高度，随着与树干距离加大，枝条δ^13C值降低，且在中部和下部枝条尤为明显．说明林线地区冷杉光合作用后存在明显的碳同位素分馏；特定冠层高度树干与枝条生长所需的碳并不是全部来源于同高度的叶片光合作用合成的碳．

英文摘要：

Based on the analysis of the distribution characteristics of δ^13C 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 postphotosynthetic δ^13C fractionation and its affecting factors. The results showed that the organ-specific difference in δ^13C yalues was highly significant （P 〈 0. 001 ）, with the sequence of trunk （-24. 19‰ ± 0. 34‰） 〉 branch （- 24.56‰ ± 0. 62‰） 〉 root （-25.05‰ ± 1.08‰） 〉 twig （-25.12‰ ± 0. 54‰） 〉 needle （- 27.25‰ ± 0. 63‰）, which suggested that an obvious postphotosynthetic δ^13C fractionation was existed between photosynthetic and non-photosynthetic organs. With increasing age of needle and twig, the δ^13C value in needle decreased significantly, while that in twig showed a reverse pattern （P 〈0.01 ）. The δ^13C value in needle increased significantly （P 〈0. 01 ） from lower canopy to higher canopy, whereas no significant difference （P 〉0. 05 ） of δ^13C value in twig was observed among different canopy heights. A significant vertical gradient of δ^13C 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 δ^13C 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 δ^13C 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.