Allelopathy by the invasive garden lupine inhibits the germination of native herbs

Abstract

Allelopathy is the stimulatory or inhibitory effect of one plant on another plant by release of phytochemicals. It can affect the competitive interactions between plants, but the strength of the effect may depend on the tissue of the donor plant and the phylogenetic relatedness of the interacting species. Here, we examined the allelopathic effects of the invasive garden lupine Lupinus polyphyllus Lindl. (Fabaceae) on six native herbs from three families (Asteraceae, Caryophyllaceae, Fabaceae). We exposed the test species to aqueous leachates prepared from root or shoot tissue of L. polyphyllus and measured germination rate and germination time. Both leachates inhibited germination in all species (13%–84%), but shoot leachate was more allelopathic than root leachate in case of Fabaceae and Caryophyllaceae. Plants from closely related Fabaceae were least affected by L. polyphyllus leachates in terms of germination rate, but leachates delayed their germination. These results demonstrate that the invasive L. polyphyllus can inhibit the germination of co-occurring native species and suggest that allelopathy likely contributes to its invasion success. Our results have implications for management of invasive L. polyphyllus populations, emphasising the importance of the removal of mown plant material to diminish inhibitory allelopathic effects on local plants.