Field assessment of Vincetoxicum rossicum secondary metabolites and their effects on species richness and V. rossicum invasion

Abstract

Vincetoxicum rossicum is an invasive vine in North America that impacts native biodiversity and ecosystem services. One of the leading hypotheses to explain the rapid proliferation of V. rossicum is its ability to produce phytotoxic chemicals that directly inhibit the growth of native plants or act indirectly by altering soil fungal communities. Although (-)-antofine, septicine, and tylophorine have been shown to exhibit antifungal properties in vitro, it is unclear whether these chemicals are biologically active and ecologically relevant under natural field conditions. In this thesis, I test the ecological relevance of (-)-antofine and other phytochemicals using field survey data from the Rouge National Urban Park, Canada. First, I test the hypothesis that plots with higher densities of V. rossicum will have higher soil concentrations of (-)-antofine, septicine, and tylophorine. Second, I test the hypothesis that species richness will be lower in plots with higher concentrations of these allelochemicals. Finally, I test the hypothesis that plots with higher allelochemical concentrations will have a direct negative effect on species richness in the following year, and an indirect positive effect on V. rossicum abundance. Soil cores were collected from twelve meadow and nine forest understory sites. In total 168 soil samples were analyzed using ultra-performance liquid chromatography with electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC/ESI-Q-TOF-MS) to measure the concentration of all three secondary metabolites. The impacts of soil allelochemicals produced by V. rossicum were compared using linear and structural equation models. Overall, the concentrations of soil allelochemicals were all positively correlated with the density of V. rossicum, and species richness was negatively correlated with allelochemical concentrations. Furthermore, our structural equation model provides empirical evidence that these allelochemicals impact V. rossicum abundance but not species richness in the following year. In addition, my findings suggest that allelochemicals produced by V. rossicum varied across habitat-type and allelochemical type, with only (-)-antofine impacting meadow habitat. My research indicates that (-)-antofine may be an important factor, but it is not sufficient, to fully account for the success of V. rossicum.