The effects of soil thickness heterogeneity on grassland plant community structure and growth of dominant species in karst area

The karst ecosystem is a special and fragile ecosystem type. In karst areas, crushed and steep terrain and a serious lack of soil resources result in strong spatial heterogeneity in soil distribution. Soil is the main medium for plants to acquire water and nutrients, and uneven soil distribution will directly affect the growth and distribution of vegetation. Therefore, a typical karst grassland community in Chongqing was selected as the research model to study community structure, species distribution, and dominant species growth status of grassland communities in different soil thickness habitats (015 cm, 1525 cm, and > 25 cm). The following results were obtained: 1) The predominant species of grassland communities in the study area were mainly annual, biennial, or herbs and, with an increase in soil thickness, woody plants gradually appeared as the dominant species of the community. The position of the dominant species in the community was more stable with an increase in soil thickness; 2) The species richness index (D1 and D2), species diversity index (SW and SN), and evenness index (R) of the plant community in the karst mountain grassland did not change significantly with soil thickness changes (P>0.05); 3) The species and importance of non-gramineous plants, mainly Compositae and legumes, increased with increasing soil thickness. The number of gramineous species decreased with an increase in soil thickness and the significance value did not change significantly; 4) Plant height, leaf area, and aboveground biomass of dominant species (Arthraxon hispidus) showed a significant upward trend with an increase in soil thickness (P<0.05). Therefore, with an increase in soil thickness, the community structure of karst grassland showed greater maturity and stability, and the growth of dominant species was significantly promoted; however, the dominance of each family and the species diversity of the community did not change significantly.