选择内蒙古锡林河流域三种草原，较系统地研究了放牧对微生物量碳(MB-C)和易分解碳(Lab-C)两种碳素组分的影响。结果表明，自由放牧22年后，羊草（Leymus chinensis）草原土壤0～10 cm和10～20 cm土层土壤微生物量碳分别下降了27.9%和12.8%；土壤易分解碳分别下降了22.0%和12.6%，自由放牧没有改变羊草草原土壤活性碳的季节变化形式。大针茅(Stipa grandis)草原0～5 cm表层和5～15 cm下层土壤微生物量碳分别下降了38.2%和12.2%。大针茅草原季节波动出现高峰的时间较羊草草原推后，基本在8月下旬，并且与地上生物量存在明显的正相关关系（p<0.001）。土壤活性碳在表征羊草草原和大针茅草原土壤的动态变化时，要敏感于土壤总有机碳。冷蒿-小禾草草原(Artemisia frigidashort bunchgrasses steppe)连续放牧11年恢复2年后，土壤各碳素组分都没有发生明显变化，但随着放牧率的增加，MB-C/Org-C比值和Lab-C/Org-C比值逐渐降低，表现为轻牧>中牧>重牧，这说明，在表征放牧对冷蒿-小禾草草原土壤的影响指示上，MB-C/Org-C和Lab-C/Org-C要比MB-C和Lab-C敏感。
Inner Mongolia grasslands are an important ecosystem of the Euro-Asia plateau. However, in recent decades, it has been severely degraded due to overgrazing, and, at the same time, soil carbon storage has changed. Because of the high background variation and diversity of natural soils, it is difficult to detect changes in soil carbon pools, especially over short time periods. Some experiments have attempted to detect changes in different fractions of soil carbon pools. In Inner Mongolia grasslands, experiments have showed there was no evident decrease of soil organic carbon for grazing. In this study, we examined the effects of grazing on soil carbon fractions: soil microbial carbon (MB-C) and soil labile carbon (Lab-C) in the grasslands of the Xilin River Basin of Inner Mongolia. MB-C was determined using the chloroform fumigation method and Lab-C was determined using the potassium permanganate oxidation method. The results indicated that after 22 years of grazing in Leymus chinensis dominated grasslands. Soil microbial biomass decreased by 27.9% and 12.8% in the 0-10 cm and 10-20 cm layers, respectively, and Lab-C decreased by 22.0% and 12.6% in the two soil layers. After 22 years of grazing in a Stipa grandis grassland, MB-C decreased by 38.2% and 12.2% in the 0-5 cm and 5-15 cm soil layers, respectively. The time at which soil microbial biomass reached a peak in S. grandis was delayed (August) as compared to L. chinensis, and MB-C was significantly correlated with aboveground grass biomass (p<0.000 1). Soil microbial carbon and Lab-C were more sensitive than SOC to the impacts of grazing on changes in soil carbon storage. There were no significant decreases in any of the soil carbon fractions in the Artemisia frigida+short bunchgrasses grassland with increases in the stocking rates, but the ratios of MB-C/total C and Lab-C/total C decreased gradually with increases in stocking rates. These results indicate that the ratios of MB-C/total C and Lab-C/total C are more sensitive indicators than MB-C and Lab-C in reflecting soil carbon changes under grazing pressure in the Artemisia frigida+short bunchgrasses grassland.