川西北高寒草地退化对土壤团聚体组成及稳定性的影响

应用干筛法与湿筛法分析了川西北高寒草地不同退化阶段土壤团聚体组成特征，选取了土壤大团聚体含量（R_0.25）、平均重量直径（MWD）、几何平均直径（GMD）和团聚体破坏率（PAD）指标，研究了退化过程土壤团聚体稳定性的变化。结果表明:未退化草地土壤机械稳定性团聚体和水稳性团聚体组成都以大团聚体（>0.25 mm）为主，而退化草地均以微团聚体（<0.25 mm）为主；随着草地退化程度加剧，大团聚体含量（R_0.25）显著降低，土壤团聚体MWD和GMD均表现为:未退化 > 轻度退化 > 中度退化 > 重度退化，PAD呈现相反的变化趋势，其中未退化到轻度退化阶段团聚体稳定性变化最为明显；未退化和轻度退化草地土壤团聚体稳定性由表层向下层递减，而中度和重度退化草地表层（0—10 cm）土壤团聚体稳定性弱于下层（10—40 cm）。这些结果表明随着高寒草地退化的加剧，土壤团聚体稳定性显著降低，轻度退化阶段是土壤结构稳定性下降的关键期，在沙化防治中应予以重视。

Effects of Degradation of Alpine Grassland on Soil Aggregates Composition and Stability in Northwestern Sichuan Province

We used dry and wet sieving methods to investigate the composition characteristics of soil in different degraded alpine grasslands in northwestern Sichuan Province. The macro-aggregates content (R_0.25), mean weight diameter (MWD), geometric mean diameter (GMD) and the percentage of aggregate destruction (PAD) of soil aggregates were selected to research the stability of soil aggregates in degradation process. The results showed that soil mechanical-stable aggregates and water-stable aggregates of non-degraded grassland was mainly composed of macro-aggregates (>0.25 mm), while micro-aggregates (<0.25 mm) were found in all degraded grasslands; with the expansion of grassland degradation, the R_0.25 decreased significantly, MWD and GMD decreased in the order: non-degraded grassland > lightly degraded grassland > moderately degraded grassland > heavily degraded grassland, while PAD showed the opposite of trend of the change, the stability of aggregates was the most obvious in the stage of non-degraded to lightly degraded; the stability of soil aggregates in non-degraded grassland and lightly degraded grassland decreased from soil surface to deep layer, but the soil aggregates in moderately degraded grassland and heavily degraded grassland soil surface (0—10 cm) were weaker than the deeplayer (10—40 cm). These results indicated that stability of aggregates reduced significantly with the degradation of alpine grassland. The lightly degraded grassland was the critical period in the decline of soil structure stability in alpine grassland, and attention should be paid to desertification control.