中文摘要：

为研究黄河源区高寒草地不同退化程度的植物根-土复合体抗剪强度特征,以青海河南县境内的黄河源区高寒草地作为研究区,进行了根-土复合体试样抗剪强度试验研究,系统分析了区内草地不同退化类型的根-土复合体抗剪强度特征及其不同退化程度之间的阈值。结果表明,区内草地其平面形态呈现不规则状椭圆形退化形态,且愈近于圆心部位草地退化相对愈严重,其退化程度表现出由外至内可依次划分为未退化区、轻度退化区、中度退化区、重度退化区;随着退化程度的加剧,原生植物种类及数量呈减少的趋势,次生植物则逐渐取代原生植物并构成优势植物种类,其结果使得根-土复合体的根系含量表现出逐渐减少的特征,根-土复合体抗剪强度亦逐渐减小;同时,根据4种类型退化区草地根-土复合体抗剪强度特征,分别确定出各退化区交替界限之间的根-土复合体抗剪强度阈值,即表现在未退化区与轻度退化区之间植物根-土复合体的黏聚力阈值为28.07kPa,轻度退化区与中度退化区复合体的黏聚力阈值为20.46kPa,中度退化区与重度退化区复合体的黏聚力阈值为9.21kPa。该项研究成果通过由力学强度角度出发定量研究草地不同退化程度的根-土复合体强度变化规律,从而对科学有效地防治该区草地退化具有重要理论研究价值和实际指导意义。

英文摘要：

The aim of this study was to determine the shear strength of the root-soi l composi te system from sites with vegetation at different stages of degradation. The selected study area was the alpine grassland in Henan County, Qinghai Province, in the source region of the Yellow River. Shear strength tests were conduc-ted to systematically analyze the characteristics of root-soil composite samples from sites with vegetation at dif- ferent stages of degradation. The results showed that the grassland in the study area had an irregular oval-shaped pattern of degradation, with more severe degradation close to the center of the oval. From the outside to inside of the irregular oval, the grassland could be divided into a non-degraded （ND） area, a slightly degrad-ed （SD） area, a moderately degraded （MD） area, and a heavily degraded （HD） area. As the degree of degrada-tion increased, the diversity and abundance of local plants decreased, and introduced plants gradually replaced local plants and became dominant. The proportion of roots in soil and the shear strength of the root-soil com-posite system decreased with increasing degradation. The shear-strength thresholds of the root-soil composite system between neighboring degradation areas were also determined. The threshold of the cohesion of the root- soil composite system between ND and SD was 28. 07 kPa, that between SD and MD was 20. 46 kPa, and that between MD and HD was 9. 21 kPa. This research to quantify differences in the strength of the root-soil com-posite system among grasslands with vegetation at different stages of degradation has theoretical value for fur-ther scientific studies, and will be useful for developing strategies to prevent and manage grassland degrada-tion.