Abstract:
Degradation is an important cause of soil erosion and environment degradation in the world. So far few have quantitatively analyzed how the level of soil degradation of grassland affects the physical, chemical and mechanical traits of topsoil in the grassland, as well as the resistance of the surface root-soil composite to erosion. This paper attempts to fill this knowledge gap by studying the impact of soil degradation triggered by rodents with the advent of denudated patches on alpine meadow topsoil on the Qinghai-Tibet Plateau in west China. Field samples were collected at 0–2 cm to test soil nutrients, physical and mechanical properties, and samples collected at 0–5 cm depth were used to test the three-dimensional pore structure of the root-soil composite in different denudated patches. A combination of macroscopic and microscopic experiments was used to study the impacts of differently degraded meadows on topsoil properties and thereby the ecological environment. Results showed that the severity of soil degradation lessened gradually from the center of the denudated patches to the periphery. Soil moisture, density and root volume in the severely degraded zone were significantly lower than in moderately and mildly degraded ones. The volumetric porosity ratio of severely degraded meadows is 4.65% and 9.55% higher than that of moderately and slightly degraded meadows, respectively, The average surface porosity increased by 4.37 and 9.58%, respectively, the average soil shear strength decreased by 36.0% and 52.3%, respectively, and the soil compactness decreased 54.8% and 90.8%, respectively, and the nutrient content of the root-soil composite also decreased with the soil degradation degree. Moreover, soil pore volume was inversely related to its shear strength that decreases quickly with degradation severity. The changes in the physical and mechanical characteristics of the topsoil in degraded meadows weakened its erosion resistance, which can lead to infertile and deteriorated soil. The strategies for restoring the degraded meadows should aim at increasing vegetation roots and litter quantity in the topsoil and stabilizing soil surface structure to create an environment for pioneering vegetation such as mosses and lichens to become established first so that the degraded meadows can recover naturally.