不同生活型树木海拔上限形成的生理机制及其对气候变化的响应

Formation and persistence of upper elevational limits of tree species are a co-result of long-term effects of climate and other multiple factors. The upper elevational tree-limits, which also act as the climatic edge of plant distribution range, are substantially a low-temperature-related limit. The dynamic changes in upper elevational tree-limit are mainly controlled by climatic factors. As a result, upper elevational tree-limits will be inevitably affected by climate change. However, very little is known so far about the responses of upper elevational tree-limit except altitudinal treeline to climate warming as well as its driving and functional mechanism. This project will focus on upper elevational tree-limits of three kinds of tree species with different life form both in the north- and in the south-facing slope of the Qinling Mountains, which are located in the region sensitive to climate change in China. Dendroecological techniques, coupled with methods of community ecology and plant physiology as well as analysis on spatiotemporal variations of age structure will be used in this study. Response of upper elevational tree-limits of the three tree species to climate change and the driving mechanism will be examined based on analyses on tree growth, regeneration, and spatiotemperal dynamics of population structure and pattern. In addition, functional mechanism of the upper elevational tree-limits of the three different life-forms will be explored whether it is related to source limitation, sink limitation, or nitrogen limitation. Species-specific and site-dependent characteristics related to dynamic changes and functional mechanism of the three tree species will also be tested. The findings of this project will be of great implication not only for understanding and predicting the effects of climate change on structure, function and dynamics of alpine forest community, but also for providing theoretical progress in effect mechanism of climate change.

物种分布海拔上限的形成与维持是气候与多重因素长期共同作用的结果。作为树木分布气候边缘的海拔上限，本质上是一条低温界限，其动态变化是由气候因素主导的，因此气候变化将不可避免的对其产生深刻影响。然而目前对林线之外的其他生活型树木海拔上限在气候变暖背景下的响应动态和驱动机制及形成机理却知之甚少。本申请项目以气候变化敏感区域秦岭南北坡三种不同生活型树木海拔上限为研究对象，综合运用树木年轮气候学、植物群落学、植物生理学和种群年龄结构时空变化分析的方法，从树木生长与更新、种群结构与格局时空动态来探讨和比较不同生活型树木海拔上限对气候变化的响应行为与驱动机制，从源限制、汇限制、氮限制的角度揭示不同生活型树木上限形成的功能机理，并分析可能的物种特异性和地理特异性特征。研究结果对深入理解和预测气候变化对山地森林植物群落结构、功能和动态的影响及其响应具有重要意义，并可为气候变化的生态响应机制提供理论进展。

物种沿海拔分布的上限是一条低温气候界限，植物个体生理活动处于极易发生变化的临界状态，对气候变化极其脆弱和敏感，气候变化所导致的山地植物生理生态适应性变化和种群特征可塑性变化必然会在物种沿海拔分布上限得到充分体现。然而目前对林线之外的其他生活型树木海拔上限在气候变暖背景下的响应动态和形成机理知之甚少。本项目以三种不同生活型树木海拔上限为研究对象，综合运用树木年轮气候学、植物群落学、植物生理学相结合的方法，从树木生长与更新、种群结构与格局时空动态来探讨和比较不同生活型树木海拔上限对气候变化的响应行为，并从生物功能角度揭示不同生活型树木上限形成的机理和可能的物种特异性特征。项目执行过程中，在秦岭南北坡三种不同生活型树木（落叶阔叶树牛皮桦、常绿针叶树巴山冷杉、落叶针叶树太白红杉）海拔上限设置了多条贯穿上限交错区的垂直固定样带（宽度30m、长度150-300米），并完成了相应的调查取样工作。一方面，从生物功能机理的角度，揭示尽管植物功能群不同，但三种树木海拔上限的形成都不是因为碳水化合物供应不足所导致，而是由于低温限制了树木对非结构性碳汇化合物的利用所致，支持生长受限假说；另一方面，尽管存在物种差异特性，但气候变暖导致了三种植物功能群树木海拔上限都出现了个体密度增加、海拔上限上移现象。项目开展过程中，按着研究计划完成了项目任务书的研究内容，较好的达到了预期研究目标，共发表SCI研究论文5篇，中文核心论文2篇，另有其他研究结果已撰写成论文在审稿中，取得了较为理想的研究成果。研究结果对深入理解和预测气候变化对山地森林植物群落结构、功能和动态的影响及其响应具有重要意义，研究结果可为山地森林资源的可持续性经营管理和开发利用提供理论指导和科学依据。