放牧对典型草原土壤有机碳及全氮的影响

Effects of grazing on soil organic carbon and total nitrogen in typical steppe

以内蒙古锡林河流域羊草Leymus chinensis典型草原作为研究对象，研究不同放牧强度及放牧制度下，土壤有机碳、全氮的含量差异，结果表明：1）土壤有机碳含量大体表现为常年放牧地高于混合放牧地，且差异明显。常年放牧地表现为轻牧〉重牧〉中牧〉围封未放牧地，混合放牧地除“轻牧＋割草”与“中牧＋割草”在20-30cm土层深度表现出显著差异以外，各个放牧强度问差异均不显著。土壤有机碳含量随着土层深度的增加而降低。2）土壤全氮在不同的放牧梯度间及不同土层深度间的变化趋势与土壤有机碳大体相同，趋势表现为轻牧〉重牧〉中牧〉围封未放牧地，而混合放牧地的变化趋势比较复杂，相比较常年放牧地，混合放牧地的全氮含量要低。全氮含量随着土层深度的增加而降低。研究结果表明重牧下有机碳含量要高于中牧，这可能是由于随着放牧强度的增加，草原植被C4植物增多而引起的。

The contents of soil organic carbon （SOC） and total nitrogen （TN） under different grazing intensity （light grazing, LG; moderate grazing, MG; heavy grazing, HG; zero grazing and fence, CK） and system in the Leymus chinensis typical steppe near the Xilin River in Inner Mongolia were studied. The result showed that 1）the SOC content of the continuous grazing land was significantly higher than the mixed grazing pasture and the order in continuous grazing pasture was LG〉HG〉MG〉CK. In the mixed utilization pasture, except LG＋hay and MG＋hay within 20 to 30 cm, the differences between different grazing intensity were not significant. The content decreased with the increase of soil depth. 2） In continuous grazing pasture, the variation pattern of soil TN was similar to SOC, i. e. , LG〉HG〉MG〉CK. In the mixed grazing pasture, the pattern was more complex, and the TN content was lower than that in continuous grazing pasture. The TN content decreased with the increase of soil depth. The result indicated that the SOC level in HG was higher than MG which might be caused by more C4 plants with the increasing of grazing intensity.