中文摘要：

高山林线作为树木分布的高度上限,是全球范围最重要的植被过渡带之一,其树木生长显著受到外界极端环境条件的影响。利用点状树木径向变化记录仪于2009年5–9月,对山西省芦芽山林线组成树种白杄（Piceameyeri）生长季内树木径向生长进行了持续的动态监测。结果表明：白杄茎干日变化主要受到树木蒸腾作用日变化的影响,茎干呈现出白天脱水收缩与夜间吸水膨胀的循环变化;生长季白杄径向生长可划分为3个不同的生长时段：1）茎干水分恢复时段,2）茎干快速生长时段,3）茎干脱水收缩时段。在茎干水分恢复时段,白杄茎干径向累积变化主要受到土壤含水量变化的影响。土壤温度是茎干快速生长时段影响茎干径向生长的主导环境因子,同时它也影响着白杄茎干径向生长的开始。在茎干脱水收缩时段,土壤温度、土壤含水量是影响茎干径向累积变化的主要环境因子。白杄径向生长最大速度出现在6月末,其主要受到光周期（即白昼长短）影响,是对林线处极端环境的一种适应。

英文摘要：

As an important ecological boundary, treeline ecotone is sensitive and vulnerable to external environ- mental changes, and tree growth at treeline is strongly constrained by the harsh environment. Our objectives were to analyze the characteristics of the stem radial growth of Picea meyeri during the growing season at the treeline of Luya Mountain, Shanxi, China and investigate the main environmental factors affecting radial growth. Methods From May to September 2009, an automatic point dendrometer was used to continuously monitor stem radial growth of P. meyeri. Environmental factors were measured by instruments synchronously. Important findings The daily variation pattern, i controlled by the daily course of tree transpiration. e., reversible stem shrinking （day） and swelling （night）, was The cumulative radial variation of P. meyeri during the grow- ing season could be divided into three distinct periods： 1） stem rehydration, 2） stem rapid growth, and 3） stem de- hydration contraction. During different growth periods, the major environmental factors controlling the stem ra- dial growth were different. Soil water content, soil temperature, soil temperature and water content were the main environmental factors corresponding to the above mentioned three growth periods, respectively. Soil temperature determined the initiation of stem radial growth of P. meyeri. Photoperiod could act as the constricting factor for the growth rate of P. meyeri at the treeline. The maximum growth rate of P. meyeri occurred in late June, around the time of maximum day length （summer solstice）, which may be a survival strategy to avoid frost damage dur-ing cold winter conditions at treeline.