2.1 Study area
The study was conducted at the Haibei National Field Research Station, Qinghai, China (37°37′ N, 101°19′E) (Fig.1a), which is situated on the Northeastern QTP at an elevation of 3200 m a.m.s.l. This area is characterized by a plateau continental monsoon climate, with well-developed seasonally frozen ground (Dai, Guo, Du, et al., 2019). The average annual air temperature is –1.7°C, with the maximum monthly temperature in July (10.1°C) and minimum monthly temperature in January (–15.0°C). The annual precipitation is about 580 mm, of which 80% falls in the growing season (i.e. from May to September). The average annual pan evaporation is approximately 1191.4 mm (Zhang et al., 2018). The soil at the study site is classified as Mat-Gryic Cambisol, which belongs to a clay loam, and has a thickness of approximately 60 – 80 cm (Dai et al., 2019). The vegetation is dominated by perennial sedge and graminoid species, including Kobresia humilis, Stipa aliena and Elymus nutans, which together constitute 60% - 80% of plant cover around the lysimeter system (Fig.1b).