Table 1 Basic information of the sample plot

In order to study the response of alpine meadow soil ecosystems to grazing disturbance under environmental constraints, alpine meadows located on mountain slopes within the study area were selected for grazing experiments of different intensities. This sample site is located on the middle slope of a semi-positive mountain slope with low soil moisture content and weak vegetation growth, which is one of the representative types of alpine meadows under environmental constraints, detailed information of which is given in Table1. The selected experimental land was fenced and prohibited from grazing in 2009 as a grazing experiment, which included one closed grazing group and three grazing groups of different intensities. The closed grazing group was CK, and three grazing groups of different intensities were light grazing, moderate grazing and heavy grazing as experimental groups to form a grazing gradient. The geographical location and layout of the experimental plots are shown in Figure 1. The area of the closed grazing group was 3×15 m² and there was no human intervention except for sampling throughout the year. The area of the other three grazing treatment groups with different intensity was 9 × 9 m. In the grazing group, the warm season grazing experiment was carried out from June to September each year. The grazing animals were Tibetan sheep. The grazing intensity treatment groups of light, heavy and heavy grazing intensity were grazed continuously for 48 hours at the beginning of each month. According to the gradient grazing intensity treatment, 3, 5 and 12 Tibetan sheep of the same age and body size were grazed in the mild, moderate and heavy grazing groups, respectively. The sheep were allowed to eat and move freely during the grazing period and were released from the experimental area 48 hours later. Soil samples were taken 15 days after the grazing experiment.