Grazing, one of the main grassland utilization modes, has notable impacts on grassland ecosystem structure and functions. However, the effects of long-term grazing on soil aggregate composition and stability are poorly understood. Based on a long-term grazing experiment platform in Inner Mongolia Stipa breviflora desert steppe established in 2004, with treatements of no grazing (control), light, moderate, and heavy grazing intensities, we studied the changes of soil aggregate composition and stability under different grazing intensities. With the measurement of relevant soil physical and chemical characteristics, we explored the main factors that affecting the stability of soil aggregates. The results showed that grazing significantly altered soil aggregate composition. Compared with control, the content of large aggregates (0.25-2 mm) was unchanged in light grazing but significantly decreased in treatments with moderate and heavy grazing intensities. Heavy grazing significantly decreased the content of small aggregates (0.053-0.25 mm), while light and moderate grazing significantly increased that of microaggregates (<0.053 mm). Soil aggregate stability was maintained at a high level under light grazing, but significantly decreased under moderate and heavy grazing treatments. Soil aggregate stability was positively correlated with macroaggregate content but negatively correlated with microaggregate content. Soil pH, bulk density, organic carbon and other physicochemical indices jointly contributed to the changes of soil aggregate composition and hence affect soil aggregate stability. In conclusion, our results showed that appropriate grazing could maintain high level of soil aggregate stability in desert steppe.
放牧作为草地的主要利用方式,对草地生态系统的结构和功能具有显著影响。目前长期放牧对草地土壤团聚体组成及其稳定性的影响还知之甚少。本研究依托2004年建立的内蒙古短花针茅荒漠草原长期放牧试验平台,设置围封禁牧(对照)、轻度、中度和重度放牧强度,研究不同放牧强度下土壤团聚体组成和稳定性的变化,并结合相关土壤理化指标探究影响土壤团聚体稳定性的主要因素。结果表明: 放牧显著改变了不同粒径土壤团聚体的组成。与对照相比,大团聚体(0.25～2 mm)含量在轻度放牧下保持不变,而在中度和重度放牧下显著下降;重度放牧显著降低了小团聚体(0.053～0.25 mm)含量,而中度和重度放牧显著增加了微团聚体(<0.053 mm)含量。土壤团聚体稳定性在轻度放牧下维持较高水平,但在中度和重度放牧下显著降低。土壤团聚体稳定性与大团聚体含量呈显著正相关,与微团聚体含量呈显著负相关。土壤pH值、容重、有机碳及其他理化性质共同作用于土壤团聚体组成进而对其稳定性产生影响。综上,对于荒漠草原而言,适度放牧可以维持较高的土壤团聚体稳定性。.
Keywords: aggregate stability; desert steppe; grazing intensity; soil aggregate.