Trade-off between shade tolerance and chemical resistance of invasive Phytolacca americana under different light levels compared with its native and exotic non-invasive congeners.
The tolerance of Phytolacca americana to low-light environment is crucial for plant growth and reproduction, which we believe may also contribute to its successful invasion to new environments. Here, a common garden experiment with light and shade treatments was used to study the effects of shading on the growth characteristics, biomass allocation and chemical substances of invasive species P. americana and its congeners. The results indicate that the invasive species grew better under low light conditions. Specifically, it displayed the highest plant height and the largest total biomass. At the same time, it stored more energy in the roots, which was manifested in the largest root-shoot ratio. Further, only the invasive species bloomed in low light. In addition, from light to shade, the reduction in biomass of each part of invasive species was the smallest, indicating that the invasive species was least affected by shade environments. Moreover, compared with its congeners, P. americana uses fewer resources for defense and more resources for growth and reproduction. These findings suggest that P. americana has stronger shade tolerance than its homologous species. When light resources are insufficient, trade-offs between secondary metabolites and growth, especially in roots, became more apparent.