物种沿海拔分布的上限是一条植物功能型特异的低温气候边缘，其形成是植物生理生态对低温长期适应的结果，但到目前基于碳‘源-汇’平衡关系的分析尚无法揭示这条低温界限形成的生物功能机理。本项目以秦岭三种不同植物功能型树木（阳生落叶阔叶树、耐阴常绿针叶树、喜光落叶针叶树）海拔上限为研究对象，在树木个体尺度上基于碳分配平衡关系，通过原位控制试验和室内模拟实验，利用植物生理学和树木生理生态学相结合的方法，探讨储存与生长兼顾的“两头下注”碳分配策略适应低温胁迫的功能调节机制，旨在阐明碳分配平衡关系对物种海拔上限形成的功能作用及其对气候变暖的响应和可能存在的植物功能型特异性。研究结果对深入理解和预测气候变暖对山地森林生态系统结构和功能的影响以及对山地森林资源的可持续性经营管理具有重要意义，并可为全球变化生态学效应研究提供新的理论进展。

The upper elevational range limit of tree species is a plant-functional-type-specific cold-temperature boundary. Its formation is attributable to the long-term adaptation of tree species’ ecophysiology to the cold temperatures. Up to now, however, the biological functional mechanism has not yet been explicitly elucidated for the formation of the upper elevational tree-limit based on the balance of carbon source-sink. This project will focus on the upper elevational tree-limits of three different plant functional types in the Qinling Mountains of north-central China (shade-intolerant broad-leaved deciduous tree, shade-tolerant evergreen conifer, shade-intolerant deciduous conifer). In situ and ex situ experiments will be conducted, and methods combined plant physiology and tree ecophysiology will be employed in this project. Functional regulating mechanism of ‘bet hedging’ carbon allocation strategy in response to cold stress (i.e., active carbon storage at the expense of growth) will be explored based on the balance relationship of the whole-tree carbon allocation. The primary objectives of this project are to: 1) test the functional effects of carbon allocation balance on the formation of the upper elevational tree-limits; 2) examine the response of the carbon allocation balance to climate warming; and 3) determine the possible species-specific characteristics among the three plant functional types. The findings of this project will be of great implication for understanding and predicting the effects of climate warming on the structure and function of alpine forest ecosystem. Also, the findings will shed lights on sustainable management of the montane forest resources, and contribute new theoretical progress to the studies of global change ecology.