Abstract
Elton’s classic diversity-invasibility hypothesis posits that diversity of resident communities increases resistance against invaders. We tested whether the diversity-invasibility relationsip might be mediated by allelopathic effects of the resident species. In a large germination experiment, we exposed seeds of six alien and six native test species to leachates of one, three, six or twelve species. The leachates tended to slightly delay germination, and almost all single-species leachates reduced the proportion of germinated seeds. Nevertheless, the overall effect of the plant leachate mixtures on the proportion of germinated seeds was not significant. This was because a higher diversity of the leachates increased the proportion of germinated seeds, particularly for native test species. Among the six alien test species, it was only the most invasive one that benefited from increased diversity of the leachates, just like the natives did. Overall, our findings suggest that allelopathy of diverse communities does not provide resistance but could actually facilitate the germination of invaders.
Highlights
With increasing globalization, more than 13,000 vascular plant species have established self-sustaining populations outside their native regions
The role of allelopathy in invasion success is fundamental to the the novel weapons hypothesis (Callaway and Ridenour 2004), which posits that some alien plants have become invasive due to the production of chemical compounds that are toxic to the naıve native plants
We found neither evidence that the alien test species suffered more from allelopathy than the native test species nor that among the alien species, the ones that are more invasive suffered less from allelopathy
Summary
More than 13,000 vascular plant species have established self-sustaining populations outside their native regions (van Kleunen et al 2015; Pysek et al 2017). It has been suggested that the high competitive ability of some invasive plants could be achieved by suppression of germination and growth of neighboring plants by allelochemicals (Baker 1974; Callaway and Aschehoug 2000; Hickman et al 2020). In support of this idea, Kalisz et al (2021) showed that of the 524 invasive plant species in their database, at least half have known allelopathic effects. Numerous studies find support for the novel weapons hypothesis (e.g. Ridenour and Callaway 2001; Abhilasha et al 2008; Gomez-Aparicio and Canham 2008; Thorpe et al 2009; Inderjit et al 2011; Becerra et al 2018), indicating that allelopathy might play an important role in plant invasions
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