中文摘要：

为了研究草原土壤退化与恢复机制,以锡林郭勒盟草原生态定位站长期定位实验为基础,采集了围栏禁牧、轻度放牧与过度放牧等放牧管理措施样地的土壤样品,提取其中的胡敏酸,综合应用元素分析、傅里叶变换红外光谱、固相魔角旋转13C核磁共振谱对放牧和围栏的羊草草原样地表层土胡敏酸的分子结构特征进行了比较分析。研究表明：在围栏禁牧和放牧条件下相比,土壤胡敏酸的分子结构特性存在明显的差异,围栏样地的胡敏酸结构其芳香度明显降低,显示出更高的脂肪族特性,羧酸官能团含量降低。经过围栏样地禁牧恢复的土壤胡敏酸结构中含有更多的来源多糖和蛋白质类母体的结构单元,而不同放牧强度之间胡敏酸的结构组成差异不大。

英文摘要：

Grazing has a lot of effects on grassland soil properties. The objective of the present study is to investigate the effects of different managements on soil humic acids. Soil samples were collected from the surface soil of four adjacent plots （ Ⅰ , Ⅱ , Ⅲ and Ⅳ） at a long-term experiment site of the Inner Mongolia Grassland Ecosystem Research Station （IMGERS）, the Chinese Academy of Sciences. The structure features of humic acids were investigated by cross-polarization magic angle spinning 13C-nu- clear magnetic resonance spectroscopy （CP/MAS 13C-NMR）, FTIR and elemental analysis. The results indicated that the humic acid extracted from the grazing plots were characterized by a higher degree of humification, including loss of polysaccharides, decrease in lignin content and increase in aromaticity. Compared with the humic substances from the grazing plots, the humic substances from fenced plots showed a lower degree of humification and were considerably more aliphatic in nature.