Abstract
Exotic invaders may possess novel biochemical weapons that native plants do not have, and these novel biochemical weapons may be more allelopathic than those from native plants to other native competitors. During range expansion, native species also encounter many new plant competitors. Thus, allelochemicals from native expanding species may also be more novel and allelopathic than those from non-expanding species to other plant competitors in the expanded range. We test this hypothesis using the native expanding Merremia boisiana and its non-expanding congener M. vitifolia in year 2012 inthe expanded range inHainan. In petridish bioassays, we found that aqueous extracts of M. boisiana leaves were often less inhibitory or more stimulatory to seed germination and seedling growth of five vegetable species than those of M. vitifolia leaves. In pot culture, we also found that aqueous leaf extracts of the two congeners could both inhibit the growth of a naturally co-occurring plant Paederia scanden, but their effects did not differ from each other. These results indicate that while allelopathy may contribute to the competitive ability of M. boisiana, it may not act as a novel weapon explaining its success in the expanded range in Hainan.
Highlights
Determining the mechanisms that facilitate species invasions is a fundamental objective for invasion ecology
Aqueous extracts of M. boisiana and M. vitifolia leaves at 0.1 g/ml concentration either had no effect or stimulated the germination rate of vegetable seeds and shoot and root growth of vegetable seedlings compared to the control, while those at 0.5 g/ml concentration inhibited the germination rate and shoot and root growth (Table 1)
Compared to aqueous extracts of M. vitifolia leaves at the concentration of 0.25 g/ml, extracts of M. boisiana leaves at the same concentration inhibited less of the seed germination, stimulated more of shoot growth, and inhibited less of root growth of B. oleracea var. capitata (Table 1)
Summary
Determining the mechanisms that facilitate species invasions is a fundamental objective for invasion ecology. The Novel Weapons Hypothesis (NWH) proposes that some exotic invaders possess novel biochemical weapons that are more allelopathic to newly encountered plants in the exotic range than to their old neighbors in the original range [1], probably because their old neighbors have adapted to these biochemical weapons after a long time of interaction. Support for this hypothesis has frequently been found in the literature. Noxious plant invaders in China were reported more likely to exert strong allelopathic effects on native plants than less noxious plant invaders [4]
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