Study on population and community characteristics of invasive plant Rorippa amphibia

To explore the spatial distribution pattern of invasive plants and its influencing factors is of great theoretical significance for better understanding the invasive mechanism of alien species. The lawn communities invaded by Rorippa amphibia in different biotopes were investigated, and the population density, coverage and other characteristics of R. amphibia were analyzed. The spatial distribution pattern of R. amphibia was studied by using seven indexes, including diffusion coefficient (C), negative binomial parameter (K), mean crowding degree (m*), cluster index (I), clustering index (PI), Cassie index (C_A) and Green index (GI). Cluster analysis and principal components analysis (PCA) were used to explore the differences of community types and the major environmental factors. The results showed that the population of R. amphibia showed aggregation distribution in different habitats. The population density, coverage and height of R. amphibia under no shade and partial shade conditions were 2.93 and 2.73 times and 4.52 and 4.79 times and 1.57 and 2.37 times of those under full shade conditions. The density, height and coverage of the population of R. amphibia were the lowest under full shade condition, and the difference between this population and the no shaded habitat was significant or extremely significant. Under partial shade, the height and coverage of R. amphibia were the highest, which were significantly different from those under full shade, and were significantly different from those under no shade in height, but no significant difference in coverage. Cluster analysis divided the investigated community samples into three associations, namely ass. Poa pratensis + R. amphibia, ass. R. amphibia + Cardamine lyrate, ass. Viola yezoensis + P. pratensis, and R. amphibia was the dominant species in two of the associations. PCA analysis showed that light intensity and soil water content were important ecological factors affecting the community type of R. amphibia.