中文摘要：

为探讨林分结构对土壤有机碳固定的影响，本文以黄土台塬的油松、沙棘、刺槐和侧柏纯林及其混交林为对象，对土壤有机碳、易氧化态、轻组、颗粒态以及可溶性有机碳进行了分析。结果表明，1）混交林可有效增加土壤不同组分有机碳含量，侧柏混交林与纯林相比增加最为明显，其土壤有机碳增加了123％和160％，易氧化态有机碳增加了161％和304％，轻组有机碳增加了1399％和482％，颗粒态有机碳增加了454％和436％，可溶性碳增加了138％和170％（0-5cm土层）；刺槐-沙棘、油松-沙棘-刺槐混交林相对改良效果较差。2）各活性有机碳间相比较，混交林对土壤易氧化态碳含量增加效果最显著，而对土壤颗粒有机碳的改善效果不甚明显。3）在0-100cm土层，轻组有机碳敏感性指标分别是总有机碳、可溶性和易氧化态有机碳的1．00-10．58、3．83-10．19和1．78-5．10倍。4）有机碳与活性有机碳组分均呈线性极显著正相关关系；轻组有机碳与颗粒有机碳二者之间的相关性大于其与其他，易氧化态碳与可溶性有机碳二者之间的相关性大于其与其他。

英文摘要：

In order to examine the effects of soil organic carbon sequestration under different plantation structures in the tablelands of Loess Plateau, in this paper, Biota orientalis, Robinia pseudoacacia, Hippophae reamnoides and Pinus tabuliformis pure and mixed planting models were selected. The soil organic carbon （SOC）, easily oxidizable organic carbon （EOC）, light fraction organic carbon （LFOC）, particulate organic carbon （POC） and dissolved organic carbon （DOC） were analyzed. The results show that the accumulation of carbon in the mixed foresdands is higher than that in the pure forestlands. Compared with the pure forestlands, the mixed forests of Biota orientalis- Robinia pseudoacacia could improve soil labile organic carbon （LOC） contents in the 0 -5 cm soil layers effectively, for example, SOC are increased by 123% and 160%, EOC are increased by 161% and 304% , LFOC are increased by 1399% and 482% , POC are increased by 454% and 436%, and DOC are increased by 138% and 170%. While the improvements in the mixed forests of Robinia pseudoacacia-Hippophae reamnoides, Pinus tabuliformis -Hippophae reamnoides-Robinia pseudoacacia are small. Among the soil LOC contents, compared with the pure forests, the soil EOC contents are improved most significantly in the mixed forests, LFOC contents are the next, while the soil POC contents are not significantly improved. The soil LFOC is more sensitive than others. In the 0 - 100 cm soil profile, the sensitivity index of LFOC is 1.00 -- 10. 58, 3.83 -- 10. 19 and 1.78 -- 5.10 times of those of the SOC, DOC and EOC respectively. The correlation coefficient and regression analysis of the organic carbon fractions show that there is a very significant linear positive correlation between SOC and LOC, and amongsoil organic carbon fractions, POC accounts for the highest percentage, LFOC for next, while DOC just a little. In addition, the correlation coefficient of between soil LFOC and POC is higher than those between soil LFOC and the others, and the correlati