Spatial distribution of vegetation and soil in aquatic-terrestrial ecotone, Li River

Abstract: In the face of ecological problems such as the shortage of water and vegetation degeneration occurred in the Li River in recent years. Research on the spatial distribution of vegetation and soil in aquatic-terrestrial ecotones in Li River aims to provide a scientific basis to vegetation restoration, landscaping, wetland protection and management and its sustainable use in aquatic-terrestrial ecotones of the Li River. This paper mainly studies aquatic-terrestrial ecotones in the Li River, which belongs to a Karst landform. According to the elevation and vegetation types of aquatic-terrestrial ecotones, we divided the study area into four gradient zones including gravel beach, grassland, shrub-grass land, and open forestland. By investigating the spatial distribution of soil and vegetation in four typical gradient zones and analyzing their distribution and correlation, the results showed that with the increase of riverbank gradient elevation, vegetation abundance, diversity trend (Shannon-Wiener plant diversity), evenness (Pielou index), dominance (Simpson index) and coverage presented an increasing trend, the number of species had become increasingly diverse, and species composition structure had become complicated. Soil bulk density increased initially and then decreased. Sand content declined significantly. Silt and clay content increased significantly, which was related to the improvement effect of vegetation. Soil organic matter decreased initially and then increased. Total nitrogen content continuously increased. Available phosphorus content presented a reducing trend that was unnatural, related to non-point source pollution on the shore of Li River, and regulating the residents' behavior is necessary. The alkaline soil pH of Karst ecotone was negatively correlated with total nitrogen content while it was positive correlated with available phosphorus content. Soil properties influence vegetation diversity. The results showed that vegetation abundance, diversity trend, evenness, dominance and coverage were positively correlated with the content of silt, clay, total nitrogen and soil organic matter, but negatively with sand content, soil bulk density, soil pH and available phosphorus content. Furthermore, the results demonstrated that the total nitrogen content was one soil factor that had the largest influence on vegetation growth. Having higher soil-nutrient content, gravel beach had considerable potential for vegetation restoration, and it was a key area in the aquatic-terrestrial ecotones. Making full use of gravel beach can be helpful to the vegetation restoration in aquatic-terrestrial ecotones in the Li River.