2.1. Study area and sampling collection

A vegetation community survey and soil sampling for this study were conducted on two separate grasslands, situated in the alpine meadow eastern edge of the Qinghai-Tibet Plateau in the administrative region of Tianzhu County, Gansu Province, China (37°11′N, 102°46′E). According to the guidance of local grassland ecological experts and herders, the A. inebrians-type degraded grassland was selected as the research area, which was open public grassland with basically the same vegetation as 35 years ago, with A. inebrians as an absolute dominant species. In 1993, it was divided into two areas: (i) one, rested in summer, had always been grazed by Tibetan sheep + yak and as a supplementary feeding site in winter, and had been fenced; and (ii) the other was still used as an open public pasture, with the same livestock grazing all year round. The distance was 20 m between cold-season grazing plus supplementary feeding pasture and four-season open public pasture, so the physical environment was similar (soil substrate and topography were the same). The altitude is 2910 m, annual mean temperature is −0.1°C, with monthly mean temperature ranging from −18.3°C in January to 12.7°C in July, and average annual accumulated temperature of 1380°C. The average annual precipitation is 416 mm, mainly concentrated in July–September and mostly terrain rain. There are only cold and warm seasons in the year, with the cold season in October–May, the warm season in June–September and the plant growth period generally April–September. The two grasslands are termed cold-season grazing plus supplementary feeding pasture (CSF) and four-season open public pasture (FOP).