Comparison of phenolic compounds and the effects of invasive and native species in East Asia: support for the novel weapons hypothesis

Abstract

One prediction of the novel weapons hypothesis (NWH) for the dominance of exotic invasive plant species is that the allelopathic effects of successful invaders will, in general, be more biochemically inhibitory to native species and microbes in invaded regions than the native plants themselves. However, no study has compared biochemical concentrations, compositions, or effects of large numbers of native species to those of large numbers of invasive species. In this context we tested the allelopathic and antimicrobial potentials of nine native plant species and nine invasive species in East Asia by comparing their broad phenolic contents and the effects of extracts made from each of the species on target plants and soil fungi. Three of the invasive species, including Eupatorium rugosum, had higher concentrations of total phenolic compounds than any of the native species, and the mean concentration of total phenolics for invasive species was 2.6 times greater than the mean for native species. Only scopoletin was novel to the invasive species, being found in all of nine invasive species, but not in the native species. More importantly, the effects of the total suites of phenolic compounds produced by invasive species differed from the effects of phenolics produced by natives. Extracts of invasive species reduced radicle growth of the three test plant species by 60-80%, but extracts of native species reduced radicle growth by only 30-50%. Extracts of invasive species reduced shoot growth of the three test species by 20-40%, but the overall effect of native species' extract was to stimulate shoot growth. The antimicrobial activity of invasive species was also significantly higher than that of native species. It should be noted that phenolics are just one component of a plant's potential allelopathic arsenal and non-phenolic compounds are likely to play a role in the total extract effect. For example, extracts of P. americana contained the lowest levels of phenolic compounds, but exhibited the strongest inhibition effect. We could not determine whether the greater inhibitory effects of the extracts from invasive species were due to novel combinations of chemicals or higher concentrations of chemicals, but our results are consistent with the predictions of the NWH.

Impact of an invader on species diversity is stronger in the non-native range than in the native range

“…It is unknown how non-water-soluble might influence cooccuring species. Other studies have reported similar results for biogeographic differences in allelopathic effects as a mechanism for the dominance of invasive plant species in their non-native ranges (Callaway and Aschehoug 2000;Callaway and Ridenour 2004;Lankau et al 2004;Wikström et al 2006;Callaway et al 2008;He et al 2009;Thorpe et al 2009;Schaffner et al 2010;Colvin and Gliessman 2011;Inderjit et al 2011a, b;Kim and Lee 2011;Svensson et al 2013) also see meta-analyses by (Lamarque et al 2011;Jeschke et al 2012).…”

Allelopathic effect of the invasive Acacia dealbata Link (Fabaceae) on two native plant species in south-central Chile

“…Additionally, this paper provides a basis for studies that explore the changes that allelochemicals may cause in chemical, physical and biological soil properties. Such alterations have been documented as part of the competitive abilities of invasive species in their non-native range (Jordan et al 2008, Kim & Lee 2011, Steinlein 2013.…”

Seasonal dependence and functional implications of macrophyte–phytoplankton allelopathic interactions

“…Many exotic plants possess secondary compounds that are novel to the native community (Callaway & Ridenour, 2004;Macel, Vos, Jansen, Putten, & Dam, 2014). These novel compounds are known to be extremely bioactive (Cappuccino & Arnason, 2006), inhibiting the growth of both native plants and phytoplankton competitors (Hilt & Gross, 2008) and, thus, improving the fitness of invasive species and providing them with a strong competitive advantage over native species (Callaway & Ridenour, 2004;Kim & Lee, 2011). A better understanding of the phytoplankton sensitivity to invasive macrophyte allelochemicals would help explain the patterns of phytoplankton succession in invaded areas.…”