Phenotypic Variation of the Invasive Plant and Analysis of Its Competitiveness With the Co-Occurring Indigenous Species .

is a malignant invasive plant in China. In this study, we sought to clarify the phenotypic variation of this plant and its competitive interaction with the indigenous species . Therefore, we established single-species planting groups for each species, with plant densities of one, two, four, or eight individuals. In addition, we set up mixed-species planting groups comprising one, two, or four individuals of both species. The results revealed significant differences in phenotypic characteristics of , such as the mean aboveground biomass (AB) in all planting, specific stem length (SSL), and specific leaf area (SLA) in single-species planting. Under the mixed-species planting, the height of was significantly lower than . The initial leaf length, plant height, and planting pattern of were found to have a significant influence on AB, whereas the initial plant height had a significant influence on growth, and the planting pattern had a significant influence on SLA. For , the coefficient of variation () values of SSL in the low-density mixed-species planting (HZ), flower bud intensity (FBI) in high-density mixed-species planting (HZ), and AB in all mixed-species planting patterns were greater than 20.0%, thereby indicating that has strong plasticity. This comparison of competitiveness indicated that the interspecific competition between and was greater than the intraspecific competition between the respective species and that the competitive capacity of was greater than that of , particularly under conditions of the medium-density mixed-species planting. Based on these findings, we conclude that can adapt to intraspecific and interspecific competition via phenotypic characteristics variation and maintain a competitive advantage. In addition, we established that in the presence of sufficient resources, the competitiveness of is strongest at medium plant densities.