2.1 Plant and soil materials
Grass seeds of drooping wildryegrass, crymophila bluegrass, Kentucky bluegrass, Chinese fescue and Siberian wildryegrass (Elymus sibiricus ) were harvested in September 2019 and provided by Tongde Forage Seed Production Base (35°15′N, 100°38′E) of Qinghai Province, which is located at the eastern Tibetan Plateau. Crop seeds of hulless barley (Hordeum vulgar var. nudum ), oat (Avena sativa ), wheat (Triticum aestivum ), quinoa (Chenopodium quinoa ) and rape (Brassica napus ) which have been harvested in 2019 were acquired from the Academy of Agriculture and Forestry Sciences, Qinghai University. These crops can grow well in the agricultural area of the province. All seeds were stored in the refrigerator at 4°C before experiment. Plants of drooping wildryegrass were collected in early August 2019, when the plant growth was in peak period. Robust whole drooping wildryegrass plants with roots were dig out with a small shovel. The plants were cut into aerial parts and below ground parts on site. The root zone soils were collected by shaking the roots parts. All plant and soil materials were put in plastic bags and kept in a refrigerator and taken back to the laboratory for experiment.