树轮中不同有机组分的可迁移性:碳同位素限定

逐轮剥离所取中国红松(Pinuskoraiensis)树盘中最近34a(1958—1991年)的年轮,粉碎后皂化分离出正己烷可溶部分、二氯甲烷可溶部分(沥青质)、不可皂化部分和纤维素,分别测定这四种物质的稳定碳同位素组成(δ13C)。虽然最近18~21a期间,前两种物质的碳同位素组成年际变化明显,但与后两种物质的碳同位素组成的正相关均没有达到显著性水平。而18~21a之前所形成树轮的前两种物质的碳同位素组成在碳同位素分析总精度范围内(±0.1‰)不呈现年际变化;与之相反,不可皂化部分和纤维素的碳同位素组成具有明显的年际变化并且在任何阶段均呈现高度显著正相关(如r=0.978,n=34,p<0.001)。这表明可皂化类脂在树轮间是可迁移的,至少经过18~21a的不同年形成的类脂的混合,其碳同位素组成逐步均一化。因此,树轮可皂化类脂的碳同位素组成(恐怕也包括氢、氧同位素组成)不能用来解译过去气候变化,全木因为含有可皂化类脂也不宜作为稳定同位素分析的目标物质。

MOBILITY OF DIFFERENT ORGANIC COMPONENTS IN TREE RINGS: CARBON ISOTOPIC CONSTRAINTS

34 rings across a time span from 1958 to 1991 were separated from a disc of Chinese red pine (Pinus koraiensis) fallen in August 1997. Hexane-soluble fraction, dichloromethane-soluble fraction, non-saponifiable fraction and cellulose were extracted and purified for carbon isotope ratio determination. During recent 18-21 years, the carbon isotope ratios of the former two fractions show a substantial variation on an annual time scale, but no significant correlation exists between the ~(13)C values of the former two and of the latter two. Before that period, the carbon isotope ratios of the former two fractions showed no annual fluctuation within the total analytical uncertainty(0.1). In contrast, the ~(13)C values of non-saponifiable fraction and cellulose always display obvious fluctuations all the year round. Moreover,the significant correlation between their carbon isotope ratios is unambiguously present within any period (e.g. r=0.978, n=34, p<0.001). This indicates saponifiable lipids in the tree rings are mobile horizontally and longitudinally. 18-21 years later, saponifiable lipids in different rings will have the same carbon (probably including hydrogen and oxygen) isotopic composition. Thus, saponifiable lipids and whole wood cannot be used for isotopic analysis in stable isotope dendroclimatology.