2.1 Soil sampling
On August 16, 2020, soil was collected from a tailing slope of an opencast coal mining area in Datan located in the Qilian Mountain (SE Gansu province) (36°50′54″ N, 102°48′05″ E, 2650-2660 m), China. The land use type around the sampling area is mainly natural grassland. The area has a typical semiarid and cold temperate climate, with mean temperature of about 16 °C and mean precipitation of about 375 mm in the growing season (June to September). The soil types is Inceptisol under the USDA Soil
Taxonomy system which characterized by nutrient impoverishment, sandy to sandy loam texture, visible soil horizons and heavy metals content do not exceed the standard. Five plots, 20×20 m2, were randomly located in a tailing slope of an opencast coal mining area, in which five soil samples(0-30 cm) were collected for each sample plot, for a total of 25 soil samples. All soil samples were thoroughly homogenized into one composite sample and sieved through a 4 mm sieve to discard coarse fragments prior to incubation experiments. Mine soil properties are shown in Table 1.