1.1 Study area
The study sites were located in the Qilian mountain nature reserve in Gansu province, China (94°10′-103°04′E, 35°50′-39°19′N). In the horizontal distribution, the vegetation gradually deteriorates from southeast to northwest, which results in the formation of four vegetation zones in an order of forest, shrub, grassland and desert. Vegetation at the vertical belt spectrum, from low altitude to high altitude, was grassland belt, forest belt and alpine meadow grassland belt. The main types of soil were mountain gray cinnamon soil, subalpine meadow soil, alpine meadow soil, alpine cold desert soil. The annual precipitation varied from 100 to 500mm, mostly from June to September, the average annual temperature was -0.6-2.0°C, the average annual relative humidity was 20%-70%, the average annual evaporation was about 1200-1400 mm, the frost-free period was 90-120 days.