To test whether the altitudinal limit of tree growth is determined by carbon shortage or by a limitation in growth, we investigated nonstructural carbohydrates and their components starch and total soluble sugars in Pinus cembra trees along an elevational gradient in the timberline ecotone of the Central Austrian Alps. NSC contents in needles, branches, stems, and coarse roots were measured throughout an entire growing season. At the tissue level, NSC contents were not significantly more abundant in treeline trees when compared to trees at lower elevations. Along our 425-m elevational transect from the closed forest to the treeline, we failed to find a stable elevational trend in the total NSC pool of entire trees and observed within season increases in the tree’s NSC pool that can be attributed to an altitudinal increase in leaf mass as needles contained the largest NSC fraction of the whole tree NSC pool. Furthermore, whole tree NSC contents were positively correlated with net photosynthetic capacity. Although our observed NSC characteristics do not support the hypothesis that treelife at their upper elevational limit is determined by an insufficient carbon balance, we found no consistent confirmation for the sink limitation hypothesis.

中文翻译：

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中奥地利阿尔卑斯山林线交错带松树移动碳水化合物的空间和季节变化

为了测试树木生长的海拔极限是由碳短缺决定还是由生长限制决定，我们沿着奥地利中部阿尔卑斯山林线交错带的海拔梯度调查了松树中的非结构碳水化合物及其成分淀粉和总可溶性糖. 在整个生长季节测量针、枝、茎和粗根中的 NSC 含量。在组织水平上，与较低海拔的树木相比，林线树木中的 NSC 含量并没有显着丰富。沿着我们从封闭森林到林木线的 425 米高程断面，我们未能在整棵树的总 NSC 池中找到稳定的海拔趋势，并观察到树的 NSC 池在季节内增加，这可归因于叶质量的海拔增加，因为针叶包含整个树 NSC 池的最大 NSC 部分. 此外，整棵树的 NSC 含量与净光合能力呈正相关。尽管我们观察到的 NSC 特征不支持海拔上限的树木生命是由碳平衡不足决定的假设，但我们没有发现对汇限制假设的一致证实。