Abstract: In this study,we studied the interactive effects of grazing,water and nitrogen on the soil aggregates stability and the soil physical and chemical characteristics in Inner Mongolia grassland. Samples were taken from 10-year long-term experimental grassland,and water and nitrogen were added to moderate and overgrazing samples,respectively. The results showed that with the increase of grazing intensity,the content of soil macroaggregates decreased,the content of microaggregates increased,the MWD and GWD significantly reduced,and the soil organic carbon contents and total nitrogen decreased significantly. Long-term water addition significantly increased the content of macroaggregates and soil organic carbon in overgrazed site,while there was not obvious change in moderate grazed site. Long-term low level nitrogen addition reduced the content of microaggregates,and increased the specific gravity of large aggregates (>0.25 mm) significantly in overgrazed site,but moderate grazed site had no significant change. In conclusion,overgrazing reduced the stability of soil aggregates;and the composition of soil aggregates was more responsive to water and nitrogen inputs in overgrazing sites than in moderate grazing sites.

Key words: Soil aggregate, Grazing, Water, Nitrogen, Typical grassland

摘要： 本研究以内蒙古草原为期十年的长期定位试验地为平台，分别在中度和过度放牧样地添加水分和氮素，研究放牧强度、水分和氮素三因子及其交互作用对土壤团聚体构成比例及稳定性的影响。结果表明：随放牧强度增加，土壤大团聚体含量减少，微团聚体含量增加，团聚体平均重量直径和几何平均直径显著减小，土壤有机碳和全氮含量显著下降；长期水分添加显著增加了过度放牧样地大团聚体含量和土壤有机碳含量，对中度放牧样地无显著影响；长期少量氮素添加显著降低过度放牧样地微团聚体含量，增加大团聚体比重，对中度放牧样地无显著影响。综上，过度放牧会降低土壤团聚体的稳定性；过度放牧样地土壤团聚体的组成对水分和氮素投入的响应比中度放牧样地更为明显。

关键词: 土壤团聚体, 放牧, 水分, 氮素, 典型草原