2.2  | Experimental materials and design
A. trifoliata was provided by The Institute of Traditional Chinese Medicine, College of Agriculture, Guizhou University. The annual seedlings with strong growth, no diseases and pests, and basically the same growth were selected as the planting materials and planted in early April. Soil samples were taken for physical and chemical properties test (Table 2), and the significance of different habitats in the same base was analyzed. As showed in Figure 1, the normal habitat is planted according to the spacing of 2 m × 3 m, while the rocky desertification habitat was planted according to the actual situation, and was divided into 10 plots. Natural rainfall, did not add any fertilizer, so that its natural growth. Six plants with similar growth were randomly selected from each plot, three of which were used to measure the biomass (every 30 days or so), and the other three were used to measure the secondary metabolites and related enzymes indexes. When sampling, the stems and leaves within 1 m of the upper part of the plant and the root within 20 cm of the soil layer were selected as materials, which were stored in self sealed bags in ice box and quickly brought back to the laboratory for quick freezing in liquid nitrogen at - 80 ℃.
TABLE 2 The soil physical and chemical properties in different habitats