Abstract
One theory concerning the invasiveness of exotic plants suggests that they exude phytotoxic compounds that are novel in areas being invaded. For most invasive plants, however, little is known about the effects of their bioactive chemicals and how novel they are in invaded areas.
From a methodological point of view, it also remains largely untested whether phytotoxicity found in vitro translates into allelopathic effects in more complex ecological settings. In this study, we tested for allelopathic effects of root exudates of the invasive plant Heracleum mantegazzianum (giant hogweed), its native congener Heracleum sphondylium (common hogweed) and two less-related native species.
We also performed chemical analyses of the invader's root exudates to identify bioactive compounds. We found that root exudates of H. mantegazzianum contain allelopathic compounds which are not likely to be furanocoumarins, but other as yet unidentified molecules.
Allelopathy of the invader detected in vitro conditions and in our garden experiment did not, however, differ from the allelopathy of the native species tested. A meta-analysis of two independent garden experiments indicated significantly negative, though similar, phytotoxic effects of H. mantegazzianum, its native congener and Dactylis glomerata in the absence of activated carbon.
Our study thus indicates that allelopathy by producing unique compounds, as predicted by the novel weapons hypothesis, is not a principal driver of the invasion success of H. mantegazzianum.