五台山高山林线树木年内径向生长动态及其对环境因子的响应

Alpine timberline, which is defined as the upper limit of altitudinal tree distribution, is one of the most conspicuous vegetation boundaries worldwide. Recently, alpine timberline can be used an ideal monitor of external environmental changes, which has important implications for global climate change research. Alpine timberline environments are generally characterized by harsh climatic conditions, which restrict tree growth and metabolic functions. Tree growth at the timberline is near its adaptation limits, and intra-annual stem radial growth may be evidently influenced by dynamic changes of limiting factors. Alpine timberline at the Wutai Mountain, which is a typical climatic timberline in warm temperate zone, was selected in our study. Using the combination of dendrometer measurements and micro-coring methods, we studied the dynamics of intra-annual stem radial growth of Larixprincipis-rupprechtii and Piceameyeri and their responses to environmental factors on the north and south slopes of timberline near Beitai region at Wutai Mountain. The main objectives of this study were to, 1) reveal the dominant environmental factors affecting stem radial growth at different time scales of day, month and season, respectively; 2) determine the leading factors influencing the critical periods of the radial growth of trees, such as the periods of start, end and maximum rate of xylem cell growth, and find out the corresponding environmental thresholds; 3) make a meta-analysis based on the data of radial variation and xylem cell growth, and establish the corresponding coupling relationship between them, which may provide a scientific basis for the long-term and accurate dynamic dendrometer monitoring of stem radial growth of trees at the alpine timberline.

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，目前已成为全球气候变化的理想“监视器”。高山林线树木生长在其适应极限附近，限制性因子的年内波动变化必然显著影响到树木的径向生长动态。本研究选取我国暖温带典型气候林线——五台山高山林线，以林线树种华北落叶松和白杄为研究对象，在五台山北台附近设置南、北坡林线样地，将树木径向变化记录仪法和微树芯法相结合，分析林线树木年内径向生长规律及其对环境因子的响应，以期探讨如下科学问题：①揭示在日、月、季节等不同时间尺度上，影响林线树木径向生长变化的主要环境因子；②确定影响茎干关键生长时期（木质部细胞生长开始、结束及最大生长速率出现时期）径向生长的主要环境因子及对应的环境因子阈值。③探讨树木径向变化数据与茎干木质部细胞生长数据的整合分析方法，建立两者之间的对应耦合关系，为今后基于树木径向变化记录仪长期准确动态监测林线树木径向生长提供科学依据。

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，目前已成为全球气候变化理想的“监视器”。本研究在五台山高山林线地区，基于树木径向变化记录仪法和微树芯法，研究了高山林线树种华北落叶松和白杄的年内径向生长规律及其对环境因子的响应。结果表明：在温暖季和寒冷季，高山林线树木茎干日变化存在着两种相反模式。在温暖季节，树木径向变化主要受到树木蒸腾作用日变化的影响，而在寒冷季节，其主要受空气温度变化引起的茎干冻融作用影响。相对较冷的10-4月茎干月均变化曲线与相对较暖的5-9月茎干月均变化曲线刚好相反。树木年内茎干径向变化可划分为明显不同的4个阶段：春季水分恢复期，夏季生长活跃期—即生长季，秋季脱水收缩期，冬季停滞稳定期。在树木年内径向生长的不同时期，影响茎干日变化的主导因子并不一致。生长季林线树木径向生长呈现出典型的“S”型曲线，茎干生长的最大速率出现在6月上中旬，其主要受到光周期的影响。土壤温度是控制林线树木茎干形成层细胞开始生长的主导因子，其土壤温度阈值为0℃，此时对应的空气温度阈值为7-8℃；基于Dendrometer方法和微树芯法获得的实验数据，分析得出的研究结果具有较好的一致性。