Understanding the physiological adaptations of non-treeline trees to environmental stress is important to understand future shifts in species composition and distribution of current treeline ecotone. The aim of the present study was to elucidate the mechanisms of the formation of the upper elevation limit of non-treeline tree species, , and the carbon allocation strategies of the species on Changbai Mountain. We employed the C in situ pulse labeling technique to trace the distribution of photosynthetically assimilated carbon in at different elevational positions (tree species at its upper elevation limit (TSAUE, 1,700 ​m a.s.l.) under treeline ecotone; tree species at a lower elevation position (TSALE, 1,400 ​m a.s.l.). We analyzed C and the non-structural carbohydrate (NSC) concentrations in various tissues following labeling. Our findings revealed a significant shift in carbon allocation in TSAUE compared to TSALE. There was a pronounced increase in δC allocation to belowground components (roots, soil, soil respiration) in TSAUE compared to TSALE. Furthermore, the C flow rate within the plant-soil-atmosphere system was faster, and the C residence time in the plant was shorter in TSAUE. The trends indicate enhanced C sink activity in belowground tissues in TSAUE, with newly assimilated C being preferentially directed there, suggesting a more conservative C allocation strategy by at higher elevations under harsher environments. Such a strategy, prioritizing C storage in roots, likely aids in withstanding winter cold stress at the expense of aboveground growth during the growing season, leading to reduced growth of TSAUE compared to TSALE. The results of the present study shed light on the adaptive mechanisms governing the upper elevation limits of non-treeline trees, and enhances our understanding of how non-treeline species might respond to ongoing climate change.

中文翻译：

---

热斑云杉的碳分配：非林线物种在海拔上限的适应策略


了解非林线树木对环境胁迫的生理适应对于了解当前林线生态交错带的物种组成和分布的未来变化非常重要。本研究的目的是阐明长白山非林线树种海拔上限的形成机制以及该树种的碳分配策略。我们采用C原位脉冲标记技术来追踪不同海拔位置的光合同化碳的分布（林线交错带下处于其海拔上限（TSAUE，1,700 m asl）的树种；处于较低海拔位置的树种（ TSALE，1,400 m asl）。我们分析了标记后各种组织中的 C 和非结构碳水化合物 (NSC) 浓度。我们的研究结果表明，与 TSALE 相比，TSAUE 中的碳分配发生了显着变化。与TSALE相比，TSAUE中的C在植物-土壤-大气系统中的流速更快，并且C在植物中的停留时间更短。趋势表明。 TSAUE 地下组织中的碳汇活动增强，新同化的碳优先定向到那里，这表明在更恶劣的环境下在较高海拔地区采取更保守的碳分配策略。这种优先考虑根部碳储存的策略可能有助于抵御冬季冷胁迫，但会牺牲生长季节的地上生长，从而导致 TSAUE 的生长比 TSALE 减少。 本研究的结果揭示了控制非林线树木海拔上限的适应机制，并增强了我们对非林线物种如何应对持续气候变化的理解。