树轮稳定碳同位素分析的采样方法--以天目山柳杉为例

Sampling strategy for carbon isotope analysis of tree rings:a case study of Cryptomeria fortunei from Mt.Tianmu,China

树轮稳定碳同位素在重建气候和环境方面得到了越来越多的应用,可是采样的方法却是多种多样,限制和影响了不同结果之间的比较。究竟在几个方位采样,在什么方位采样,既经济方便又能比较好的反映一棵树的稳定碳同位素变化过程与趋势,还没有确切的答案。研究利用来自天目山的两个柳杉树盘的多方位的和整轮的碳同位素测试数据(共计642个),通过不同方位和不同方位组合的平均碳同位素序列与整轮碳同位素序列的关系的多角度的考查、分析发现,并不是采样的方位数越多越好,选择2～4个方位采样合并分析树轮稳定碳同位素,既经济方便又能比较好的反映一棵树的δ13C变化过程与趋势。在两个或者3个方位采样时,方位之间呈钝角关系时,其代表性最好。4个方位采样时,一般使用的"十字交叉法"并不是最好的选择,建议采样的方位之间尽可能多的成钝角关系。如果条件限制只能采集一个方位的样品,采集向阳一侧的树芯,其代表性最好。

Tree-ring δ^13C analysis has been widely used in reconstructing past climate and environment. However, it is difficult to correlate the results from samples taken with different sampling strategy. It is still an open question, how to take sample, in which radii to take sample, that the δ^13C of the samples can represent the tree δ^13C trend better and more efficient. To address the issue, we analyze the correlation and similarity of the different radii sequence and the different combination sequence with the full- ring-sample sequences, based on 642 δ^13C data of cellulose fixed in tree-ring at 8 different radii of two Cryptomeriafortunei tree disks from Mt. Tianmu, a subtropical mountain of China. It suggests that 2 to 4 radii mixture sample is the better and more efficient choice for the tree-ring δ^13C analysis. It had better to take samples at obtuse angle with each other when to take the samples are taken in ＂cross＂ relation, at obtuse angle with each other, the better the core in the sunny aspect has the better samples at two or three radii. When to take four samples in one tree, but the analysis shows it is not the best choice. The more the samples the representation of the samples. If, sometimes, only one core can representation of the tree.