中文摘要：

通过对内蒙古锡林河流域叽加尔针茅草原、羊草草原和大针茅草原3种草原群落不同层位土壤样品碳素含量的测定和统计分析，探讨了农垦及放牧对该区主要草原土壤类型有机碳及无机碳的影响。结果表明：（1）贝加尔针茅草原开垦为农田30a后，与未开垦的打草场相比，农山1m土层内的土壤有机碳含量明显下降，且农田0—10cm和10～20cm土壤层有机碳含量趋于一致。（2）放牧使羊草草原平和大针茅草原表层的土壤有机碳含量下降，较深层的土壤有机碳含量升高。放牧强度较大、较干旱的大针茅草原0．20cm下降，30cm以下升高，放牧强度较小较湿润的羊草草原0～10cm下降，10cm以下升高。（3）贝加尔针茅草原开垦为农田使1m土层内的土壤无机碳含量升高，钙积化位置变浅。（4）放牧使羊草草原和大针茅草原1m土层内的土壤无机碳含量下降，钙积化位置加深，放牧强度较大、较干旱的大针茅草原表现尤为明显。（5）草地开垦为农田，在使土壤有机碳的含量降低的同时，也增加了士壤无机碳的含龄；放牧在使草原表层土壤有机碳含量减少、深层有机碳含量增加的同时，也减少了无机碳的含量。

英文摘要：

The eontents of soil organic carbon （SOC）and soil inorganic carbon（ S1C ）in different soil layers within 1 m depths in three different kinds of steppes （Stipa baicalensis steppe, Leymus chi,ensis steppe and Stipa grandis steppe ）, in the Xilin River Basin of hmer Mongolia, China , were determined in order to investigating effects of cultivating and grazing on the soil carbon in temperate grassland. The results showed that： （ 1 ）The content of SOC in the soil layers within 1 m depth obviously decreased in croplands which had been cultivated from the Stipa baicalensis steppe for 30 years compared with those of the Stipa baicalensis steppe. The content of SOC tended to accord between 0-10 cm and 10-20 cm depth soil layers in croplands after 30 years of cultivating. （2）Grazing resulted in the decrease of the content of SOC in shallow soil layers and the increase of the content of SOC in deep soil layers in the Leymus chinensis steppe and the Stipa grandis steppe. The content of SOC decreased in 0-20 cm depth soil layers and increased in 30-100 cm depth soil layers in the Stipa grandis steppe. The content of SOC decreased in 0-10 cm depth soil layer and increased in 10-100 cm depth soil layers in the Leymus chinensis steppe. The reason might be that grazing intensity and soil moisture of the Stipa grandis steppe was heavier and lower than the Leymus chinensis steppe. （3）The content of SIC in the 1 m depth soil layer was higher in cropland reclaimed from the Stipa baicalensis steppe than in the Stipa baicalensis steppe, and the place of calcic horizon was shallower in the cropland than in the Stipa baicalensis steppe. （4）As a result of grazing, the contents of SIC in the soil layers within 1 m depth declined in the Leymus chinensis steppe and the Stipa grandis steppe, and the contents had more intense decrease in the Stipa grandis steppe than in the Leymus chinensis steppe because the Stipa grandis steppe had a stronger grazing intensity, a lower primary productivity, a lower plant species