Characteristics of the grass felt layer and soil moisture in alpine meadows at the southern foot of the Qilian Mountains under different grazing intensities

To investigate the effects of grazing intensity on the alpine meadow felt layer and its soil moisture characteristics, this study was conducted to analyze the effects of different grazing intensities (light, medium, heavy, and severe) on the thickness, root-to-soil ratio, hardness, shear strength, bulk weight, porosity, saturated hydraulic conductivity, and water-holding capacity of the alpine meadow felt layer at the southern foot of the Qilian Mountains. The results showed that: 1) with the increase in grazing intensity, the plant community structure was first stable and then significantly changed. The importance values of grasses, sedges and weeds were stable, from light to heavy grazing. Compared with heavy grazing, the importance value of gramineous plants in extremely heavy grazing increased significantly to 3.95%, and the importance values of sedges and weeds increased to 11.76% and 84.29%, respectively. 2) The thickness of the grass carpet layer and root-to-soil ratio both tended to increase with grazing intensity, reaching a maximum at very heavy grazing (6.78 cm, 2.55%, respectively), both of which increased significantly compared with light grazing by 212.44%, and 212.50%, respectively. Soil hardness did not change significantly with increasing grazing intensity and remained stable at 18.95 kg·cm⁻². Soil shear strength tended to increase first and then stabilize, with a maximum value of 2 kg·cm⁻² in the medium grazing sample. Soil bulk density increased first and then stabilized with the increase in grazing intensity, and significantly decreased to 0.59 g·cm⁻³ in the heavy grazing plot. The bulk density of the felt layer in the extremely heavy grazing plot was 41.54% higher than that in the heavy grazing plot. The total porosity and capillary porosity tended to increase and then decrease with grazing intensity. 3) The maximum water holding capacity, capillary water-holding capacity, field water-holding capacity, and saturated hydraulic conductivity tended to increase and then decrease with increasing grazing intensity. 4) There was a significant positive correlation between the thickness of the felt layer and the importance of sedge, root-to-soil ratio, shear strength, hardness, maximum water holding capacity, capillary water holding capacity, and field water-holding capacity. The results of the redundancy analysis showed that the soil capacity and shear strength were the most significant factors influencing the moisture characteristics of the felt layer. In conclusion, maintaining a continuous layer of grass carpet can not only ensure the balance of water-holding function to a certain extent, but also buffer the damage to the plant community and soil structure caused by external factors, which is the key to the sustainable use and conservation of alpine meadows.