Autotoxic effects of the leachates from the invasive Eupatorium adenophorum in vitro and in soil

Eupatorium adenophorum (croftonweed), one of the most destructive alien species in China, has been demonstrated or indicated to have inhibitory effects on other species in laboratory bioassay. However, allelopathic compounds of E. adenophorum may play other roles more than interspecific interference. Here we investigated whether E. adenophorum aqueous leachates could influence conspecific seed germination and seedling growth with laboratory bioassay and found that it could inhibit seed germination and reduce seedling root elongation of E. adenophorum. Then we examined interactions between E. adenophorum leachate and natural soil on germination and seedling growth of E. adenophorum itself. The results showed that soil from different habitats altered the allelopathic effects usually observed in laboratory bioassay. In the heavily invaded site, E. adenophorum were inhibited by E. adenophorum leachates; whereas, in two lightly invaded sites, germination and seedling growth of E. adenophorum was significantly facilitated. We can infer that allelochemicals from E. adenophorum play a dramatic role in regulating its population density.