中文摘要：

封育是当前恢复和改良内蒙古草地的重要措施，也是实现草地固碳效应最有效的途径之一。本文利用内蒙古封育32年和自由放牧的羊草草地，分析了其土壤有机碳组分、土壤团聚体和土壤腐殖质组分碳含量的变化，并运用13 C核磁共振波普法对土壤腐殖质的有机碳组分进行波普分析，探讨了长期封育对羊草草地土壤有机碳组分和土壤有机质结构的影响，期望能为科学地评估长期封育状况下草地固碳效应及其稳定性提供理论依据。实验结果表明：长期封育显著提高了草地土壤有机碳含量；在土壤有机碳组分中，除土壤微生物碳（MBC ）含量降低外，其碳组分含量都相应增加。其中，易氧化有机碳（EOC）含量增加最为明显，长期封育草地是自由放牧草地土壤的4．53倍；长期封育显著提高了草地土壤0．25～2 mm 团聚体所占比例及其有机碳含量；长期封育提高了草地土壤腐殖质中的胡敏酸碳（HAC）、胡敏素碳（HUC）含量和胡敏酸／腐殖质碳，降低了富里酸碳（FAC）的含量，封育草地土壤的 H AC／FAC是自由放牧草地土壤的5．66倍。此外，长期封育草地土壤的脂族碳含量显著增加，芳香度相应增加，疏水碳／亲水碳增大。总之，长期封育不仅提高了草地土壤有机碳贮量，还能改善草地土壤结构、增强土壤有机碳的稳定性。

英文摘要：

Grazing exclusion (GE)is an important method for restoring grasslands and a useful approach for un-derstanding soil carbon (C)sequestration in temperate grasslands.Using the paired sample method C in the soil fractions,soil aggregates and soil humus was determined for grazed and ungrazed grassland in Inner Mon-golia,China;grazing exclusion (GE)had been imposed for 32 years in the un-grazed grassland.To reveal the influence of GE on the structure of soil organic matter 13 C-NMR (Nuclear Magnetic Resonance)spectroscopy was used to analyze the organic C fractions in the soil humus.The main objective was to provide a theoretical basis for scientifically evaluating the effect of GE on the sequestration and stability of C in Inner Mongolian grassland soils.The results showed that long-term GE significantly enhanced soil C content.The C content in all other fractions,except for soil microbial biomass C (MBC),increased correspondingly.The oxidizable or-ganic C in the GE grassland was 4.5 times that of grazed grassland.GE significantly improved the proportion of 0.25-2.00 mm diameter macro-aggregates and their organic C content.GE increased humic acid C (HAC), humin C (HUC)and the soil precipitate ratio (PQ),but decreased fulvic acid C (FAC).Consequently,the HAC:FAC ratio in GE grassland was 5.66 times that of grazed grassland.Additionally,aliphatic C content, aromaticity and the alkyl:O-alkyl C ratio increased in the GE grassland.In summary;GE increased soil organ-ic C,improved the soil structure and enhanced the stability of soil organic matter of Inner Mongolian grass-lands .