The role of allelopathy in plant invasion: evolutionary change vs. community response in Impatiens glandulifera

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Invasive plants present major threats to biodiversity and ecosystem processes as they competitively exclude neighbouring plants at their invasive range. Allelopathy, which is the suppression of neighbouring plants by plant-released chemicals, has been suggested as a mechanism facilitating their invasive success and competitive superiority. Particularly, the Novel Weapons Hypothesis (NWH) suggests that the allelochemicals produced by some invasive plants are novel to their invasive-range neighbours due to lack of co-adaptations, and hence provide a competitive advantage. However, a highly neglected aspect in the study of invasive plants is the possible evolution of increased allelopathic ability. Such rapid evolution of increased allelochemical production at the invasive range is predicted due to the competitive advantage it provides and as a result of release from specialist enemies, such as pathogens and herbivores. Here, I suggest a comprehensive study that will examine both the NWH and the hypothesis of evolutionary increased allelopathy in one of the most invasive plant species in Europe, Impatiens glandulifera, whose allelopathic effects, though recognized, are not yet fully established. The role of allelopathy in the invasive success of this species will be determined in a set of novel experiments that will compare both changes in the production of allelochemicals by native and invasive genotypes as well as the responses of the native and invasive-range communities to these chemicals. This study will address some key aspects that, although crucial to the study of invasive plants, are still seldom studied. These include the allelopathic effects on both coexisting plants and soil biota across the biogeographic range as well as across the invasion process between initial and late stages of invasion. The study will also address the potential genetic correlation between the production of allelopathic and anti-herbivore-compounds in invasive and native genotypes. The results of this study are expected to yield insight as to the invasive nature of I. glandulifera, for which almost no knowledge is available on biogeographic differences in either its invasive characteristics or the community response to it. The overall findings could enhance our understanding of invasion process and elucidate the evolutionary forces determining them as well as provide recommendations for management practices for control of I. glandulifera.