Abstract: In order to charity the influence of grassland cover change on soil structure in the source area of the Yangtze River,this study analyzed the distribution and stability characteristics of soil aggregates under different vegetation coverage in alpine and swamp meadow. The results showed that the soil aggregates in alpine meadow were mainly distributed in the range of 2~0.25 mm and 0.25~0.053 mm,and the soil aggregates in swamp meadow were relatively uniform distributed among different particle size. In this alpine meadow,the content of soil aggregates of >0.25 mm (WR_0.25) in high coverage grassland was higher than that in moderate coverage grassland,and the WR_0.25 of low coverage grassland was significantly higher than that of high and moderate coverage grassland along with the deepening of soil layer. Besides the surface soil of 0~10 cm,WR_0.25 of high coverage grassland was significantly higher than that of moderate and low coverage grassland in swamp meadow. There were no significant differences in the mean weight diameter (MWD) and geometric mean diameter (GMD) of the soil aggregates in 0~10 cm depth in alpine meadow under different vegetation coverage,while significant differences were found in the 10~20 cm and 20~40 cm depth with low coverage > high coverage > moderate coverage. The MWD and GMD of soil aggregates in swamp meadow gradually decreased with the decreasing of vegetation coverage and the deepening of soil layers. The soil aggregates destruction rate (PAD) of moderate coverage grassland was the largest,and its stability was the worst. The stability of soil aggregates of high coverage grassland was the best. There was no significant difference in the stability of soil aggregates in alpine meadow among different soil layers,while the stability of the soil aggregates of swamp meadow declined with the deepening of soil layers. These results showed that WR_0.25 and PAD can better evaluate the stability of soil aggregates;the response of soil aggregates in swamp meadow to vegetation cover change is more sensitive than that of alpine meadow. The results are helpful to strengthen the understanding of soil protection mechanism in the source area of the Yangtze River under the background of vegetation cover change.

Key words: Vegetation coverage change, Soil aggregate stability, Alpine meadow, Swamp meadow, The source region of the Yangtze River

摘要： 为了明确长江源区草地覆盖变化对土壤结构的影响，本研究以高寒草甸和沼泽草甸2种草地为研究对象，分析了不同植被覆盖度下土壤团聚体分布和稳定性特征。结果显示：高寒草甸土壤团聚体主要分布在2~0.25 mm和0.25~0.053 mm粒径范围内，沼泽草甸土壤团聚体在不同粒径范围内分布相对均匀；高寒草甸土壤大于0.25 mm团聚体含量（WR_0.25）表现为高覆盖度草地高于中覆盖度草地，随土层加深，低覆盖度草地WR_0.25显著高于高覆盖度草地和中覆盖度草地，除表层0~10 cm土壤外，高覆盖度沼泽草甸土壤WR_0.25显著高于中覆盖度和低覆盖度土壤；不同植被覆盖度下高寒草甸表层0~10 cm土壤团聚体平均重量直径（Mean weight diameter，MWD）和几何平均直径（Geometric mean diameter，GMD）无显著差异，在10~20 cm和20~40 cm土层差异显著，表现为低覆盖度 > 高覆盖度 > 中覆盖度，沼泽草甸土壤团聚体MWD和GMD则随草地植被覆盖度降低和土层加深而逐渐减小；中覆盖度草地土壤团聚体破坏率（Aggregate destruction rate，PAD）最大，其稳定性最差；高覆盖度草地土壤团聚体稳定性最好；在不同土层深度上，高寒草甸土壤团聚体稳定性无显著差异，沼泽草甸土壤随土层加深团聚体稳定性变差。本研究结果表明WR_0.25和PAD能够更好地评价土壤团聚体稳定性，而沼泽草甸土壤团聚体对植被覆盖变化的响应更为敏感。本研究结果有利于加强植被覆盖变化背景下对长江源区土壤保护机制的认识。

关键词: 植被覆盖度变化, 土壤团聚体稳定性, 高寒草甸, 沼泽草甸, 长江源区