Impatiens

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

01.12.2012 bis 30.11.2014

A key hypothesis that has been proposed to explain plants’ invasive success suggests that some invasive plants produce allelochemicals that are novel and therefore highly inhibitory against naïve neighbours at the introduced range (Novel Weapons Hypothesis). However, a seldom-studied hypothesis suggests that invasive populations could not only possess novel weapons, but might also evolve their enhanced production. Moreover, so far no study has examined both the novelty and evolution of allelopathic effects. Here, we examined these two hypotheses in a set of experiments with the highly invasive plant Impatiens glandulifera. In the first experiment, we examined the evolution of allelopathic ability by comparing the inhibitory effects of leaf extracts from native vs. invasive I. glandulifera on the germination success of its dominant neighbour Urtica dioica. In the following experiments, we examined the NWH by comparing the germination success of U. dioica seeds collected at the native vs. invasive range of I. glandulifera, in response to either leaf extracts or soil trained with invasive I. glandulifera. Invasive I. glandulifera exerted a stronger inhibitory effect on the germination of U. dioica compared to their native counterparts, providing support for biogeographic differences in allelopathic potential. However, there was no difference in the response to this allelopathic effect between U. dioica from the native vs. invasive range of I. glandulifera, either with leaf extracts or trained soil, thus not supporting the NWH, and suggesting that increased allelopathy in invasive I. glandulifera could have been selected for by other processes. The results of this study suggest that enhanced allelopathy might evolve at the invasive range and facilitate invasion success. This calls for biogeographical studies that will examine not only the novelty but also the evolution of allelopathic effects in invasive plants.