Cross-continental shifts of ecological strategy in a global plant invader

Abstract

Plant invasions are a global problem that requires studying plants and their environmental associations across native and introduced ranges. We surveyed 150 populations of Japanese knotweed, a key invader of the temperate zone, along 2000 km transects in native China and the introduced ranges of Europe and North America. We found that larger plants and denser populations in the introduced ranges were associated with shifts in leaf economy and chemical defenses. Introduced knotweed populations had higher SLA but reduced leaf chlorophyll, lignin, C:N and leaf toughness along with altered leaf tannins, flavonoids and alkaloids. We found three distinct multivariate knotweed phenotypes primarily in the introduced ranges, and two phenotype clusters mainly in native populations. Decreased herbivore and pathogen impacts in invasive populations and changes in environmental associations indicate that enemy release and novel habitat conditions might have driven the emergence of novel ecological strategies in this global plant invader.