Enhanced allelopathy and competitive ability of invasive plant Solidago canadensis in its introduced range

Aims Why invasive plants are more competitive in their introduced range than native range is still an unanswered question in plant invasion ecology.Here,we used the model invasive plant Solidago canaden-sis to test a hypothesis that enhanced production of allelopathic compounds results in greater competitive ability of invasive plants in the invaded range rather than in the native range.We also exam-ined the degree to which the allelopathy contributes increased com-petitive ability of S.canadensis in the invaded range.Methods We compared allelochemical production by S.canadensis growing in its native area(the USA)and invaded area(China)and also by populations that were collected from the two countries and grown together in a'common garden'greenhouse experiment.We also tested the allelopathic effects of S.canadensis collected from either the USA or China on the germination of Kummerowia striata(a native plant in China).Finally,we conducted a common garden,greenhouse experiment in which K.striata was grown in monocul-ture or with S.canadensis from the USA or China to test the effects of allopathy on plant-plant competition with suitable controls such as adding activated carbon to the soil to absorb the allelochemicals and thereby eliminating any corresponding allopathic effects.Important findings Allelochemical contents(total phenolics,total flavones and total saponins)and allelopathic effects were greater in S.canadensis sampled from China than those from the USA as demonstrated in a field survey and a common garden experiment.Inhibition of K.stri-ata germination using S.canadensis extracts or previously grown in soil was greater using samples from China than from the USA.The competitive ability of S.canadensis against K.striata was also greater for plants originating from China than those from the USA.Allelopathy could explain about 46%of the difference.These find-ings demonstrated that S.canadensis has evolved to be more allelo-pathic and competitive in the introduced range and that allelopathy significantly contributes to increased competitiveness for this inva-sive species.