川西亚高山不同海拔岷江冷杉树轮碳稳定同位素对气候的响应

树木年轮(简称树轮)碳稳定同位素技术是研究树轮气候学的一种有效方法。利用四川卧龙亚高山暗针叶林不同海拔高度岷江冷杉树轮样本资料,提取该树轮稳定碳同位素(δ13C)和去趋势序列(DS),研究其树轮碳稳定同位素序列对气候要素(降水、月平均温度和月平均相对湿度)的响应关系,初步揭示了在全球气候变化背景下,川西亚高山森林岷江冷杉树木生长对气候因子变化(气候变暖、降水减少等)的响应方式。主要结论有:(1)岷江冷杉树轮δ13C组成变化范围为-23.33‰—-26.31‰,平均值为-24.91‰,变异系数为-0.011—-0.038,并表现出较强的一阶自相关;其对环境变化有较好的指示作用,表明岷江冷杉树轮δ13C组成在年际变化中较为稳定。(2)低海拔的岷江冷杉树轮δ13C分馏主要与当年8月月平均相对湿度和当年12月月平均温度相关性显著(P0.05);高海拔岷江冷杉树轮δ13C分馏主要与上一年8月月平均相对湿度和当年4月月平均温度相关性显著(P0.05);中海拔的岷江冷杉树轮δ13C分馏主要与上一年1、11月月平均温度和当年2、11月月平均温度相关性显著(P0.05),冬季温度是中海拔区岷江冷杉树木生长的限制因子,且具有明显的"滞后效应"。川西卧龙亚高山暗针叶林岷江冷杉树木径向生长主要受到气温的制约,从生物学基础上阐明了树木生长与环境的关系,冬季温度的升高,有利于植物生长期的提前,植物生长旺盛,抗旱能力减弱;同时证明了建群种岷江冷杉对雨水的依赖很小,这有利于植物生存,且维持了该植物群落的稳定性。该研究弥补了我国青藏高原高海拔地区气象台站稀少、观测资料时间短缺,为预测未来气候变化对岷江冷杉树木径向生长变化提供了科学的依据。

Relationships of stable carbon isotope of Abies faxoniana tree-rings to climate in sub-alpine forest in Western Sichuan

The tree-ring stable isotope technique is an effective approach to climate reconstruction and to establishment of tree responses to environmental factors. In this study, the tree-ring samples of Abies faxoniana from a sub-alpine forest of Wolong in Western Sichuan were used to develop the tree-ring width chronology and stable carbon isotope series based on the standard dendrochronology methods and the stable carbon isotope techniques. The Wolong Nature Reserve in Western Sichuan is located in a transition zone from the Chengdu plain to the Tibeten Platau, with a warm and moist summer and cold and dry winter. Abies faxoniana is the dominant tree species of the sub-alpine forests at the elevation of 2600-3200 m. Tree ring data were collected in 2010 along an elevation gradient (at 2750, 2950, 3150 m). Climate data were obtained from two nearby national climate stations, Dujiangyan (103°34'E,30°59'N) and Xiaojin (102°21'E,31°N). Isotopic analyses were done at the Chinese Academy of Forestry.With the data and analyses, we established responses of Abies faxoniana tree-ring carbon stable isotope composition to several climatic factors (e.g., precipitation, mean month temperature, and mean month relative humidity). The main results of this study are as follows: 1) The carbon stable isotope series of Abies faxoniana (1904-2009) varied from -23.33‰ to -26.31‰ with the average value of -24.91‰, with the coefficient of variation ranging from -0.011 to -0.038. The carbon stable isotope series showed strong first-order autocorrelation (i.e., 0.651, 0.936, and 0.333 along the elevation gradient).2) The tree-ring carbon stable isotope composition showed similar trends at the same altitude, while the isotope composition displayed different trends as altitudes change. However, the relationships between the tree-ring carbon stable isotope composition and climatic factors were complicated. The tree-ring detrend series (DS) values from the lower altitude showed a significant positive correlation to the mean monthly temperature of the December of the current year and the mean monthly relatively humidity of the August in the previous year (P < 0.05). The tree-ring DS values from the higher altitude showed a significant positive correlation to the mean monthly temperature of the April of the current year and the mean monthly relatively humidity of the August in the previous year (P < 0.05). The tree-ring DS values from the mid-altitude showed a significant positive correlation to the mean monthly temperature of the February and November of the current year and the January and November in the previous year (P < 0.05). The most sensitive variable to the DS values was the winter temperature with a strong "lag effect".The results indicated that tree ring growth of Abies faxoniana in sub-alpine is mainly constrained by temperature with little dependence on rainfall. Thus, a warming climate should help improve the radial growth rate and the survival capability of Abies faxoniana, and this in turn should increase the stability of sub-alpine dark forests in Western Sichuan. The results should help alleviate the inadequacies of doing research in Qinghai-Tibeat plateau with fewer meteorological stations and shorter observation periods, and provide baseline data for studying responses of conifer trees to climate change in the region.