Interactions between environmental variables in anthropogenically disturbed environments and physiological traits of invasive species may help explain reasons for invasive species' establishment in new areas. Here we analyze how soil contamination along roadsides may influence the establishment of Conium maculatum (poison hemlock) in Cook County, IL, USA. We combine analyses that: (1) characterize the soil and measure concentrations of heavy metals and polycyclic aromatic hydrocarbons (PAHs) where Conium is growing; (2) assess the genetic diversity and structure of individuals among nine known populations; and (3) test for tolerance to heavy metals and evidence for local soil growth advantage with greenhouse establishment experiments. We found elevated levels of metals and PAHs in the soil where Conium was growing. Specifically, arsenic (As), cadmium (Cd), and lead (Pb) were found at elevated levels relative to U.S. EPA ecological contamination thresholds. In a greenhouse study we found that Conium is more tolerant of soils containing heavy metals (As, Cd, Pb) than two native species. For the genetic analysis a total of 217 individuals (approximately 20–30 per population) were scored with 5 ISSR primers, yielding 114 variable loci. We found high levels of genetic diversity in all populations but little genetic structure or differentiation among populations. Although Conium shows a general tolerance to contamination, we found few significant associations between genetic diversity metrics and a suite of measured environmental and spatial parameters. Soil contamination is not driving the peculiar spatial distribution of Conium in Cook County, but these findings indicate that Conium is likely establishing in the Chicago region partially due to its ability to tolerate high levels of metal contamination.
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