采用同步辐射软X射线XANES(X-ray absorption near edge structure)与SR-FTIR(synchrotron radiation-fourier transform infrared spectroscopy)光谱技术分析云雾山退耕草地土壤<0.25 mm团聚体有机碳结构变化。 SR-FTIR测定结果的定性分析表明， 与坡耕地相比， 随退耕年限增加， 退耕草地土壤脂肪C特征峰吸收增强， 芳香C、 醇C、 羧基C、 多糖C吸收峰变化不明显; SR-FTIR半定量分析表明， 与坡耕地相比， 退耕草地土壤有机碳各官能团相对含量都有所增加， 随退耕年限增加， 0～5 cm和10～20 cm两土层土壤脂肪C、 醇C相对百分量增加幅度较大， 芳香C增加幅度较小。 XANES与SR-FTIR测定结果基本一致， 对两种方法测定的相同有机碳官能团(芳香C)的相对含量进行T检验， 两种方法测定结果差异不显著（P>0.05）， 表明采用XANES测定退耕草地土壤有机碳结构变化是可行的。

Synchrotron radiation soft X-ray and SR-FTIR spectroscopy technique were used to study the change of soil organic carbon(SOC) structure in ＜0.25 mm aggregate soil from fallowing grasslands of Yun-wu mountains. Results obtained by SR-FTIR technique were qualitatively analyzed, which indicated that compared with slope farmland, the peak intensity of aliphatic-C from fallowing grasslands significantly increased, while peaks intensity of aromatic-C, alcohols-C, carboxyl-C, polysaccharide-C didn’t significantly change with increasing years of fallowing. Results obtained by SR-FTIR technique were semiquantitatively analyzed, which showed that compared with slope farmland, the relative content of functional groups from fallowing grasslands SOC was increased, the growing rate of aliphatic-C, alcohols-C in 0～5 cm and 10～20 cm soil horizon was greater than growing rate of aromatic-C. Results obtained by soft X-ray technique are consistent with SR-FTIR, and the relative content of the same functional groups (aliphatic-C, aromatic-C) gained by two determination methods were T-tested, which was not significant (P>0.05), indicating that using synchrotron radiation soft X-ray for the determination of SOC structural change of fallowing grasslands is feasible.