2.2. Field investigation and sample collection
Complete plant individuals with vigorous growth were collected from April to May 2022. In order to avoid the impact of developmental stages, we uniformly sampled at the peak flowering period of each species. The seven sampling sites were set up in the study area (Fig. 1). For eliminating the influence of terrain factors, we have ensured the similarity of the terrain of the seven sampling sites when setting up the quadrat. At each sampling site, 10m × 10m quadrat was set, and the plant height and root collar diameter of each plant in the quadrat were investigated. The average value was taken as the standard sample for sampling.