Congeneric comparison of allelopathic and autotoxic effects of four Solidago species.
The invasive species Solidago canadensis and S. gigantea are known for having the potential to inhibit their neighbours through allelopathy. However, there are no data on allelopathic properties of the natural interspecific hybrid S. ×niederederi and no investigations comparing the allelopathic potential of native and invasive Solidago species. We therefore studied the allelopathic effect of aqueous leaf extracts of S. virgaurea, S. canadensis, S. gigantea and S. ×niederederi on two congeneric pairs of species (Festuca and Solidago) occurring naturally in communities with the tested Solidago species. Germination and seedling growth of Festuca rubra were inhibited by all Solidago extracts more than were those characteristics of F. pratensis, while S. canadensis was more sensitive to its own and congeneric extracts than was S. ×niederederi. The effect of leaf type (green or withered) on Festuca seedling growth was target species-specific, while seed germination was more suppressed by green leaf extracts. The results of this study do not support the hypothesis that invasive plant species have stronger persistent allelopathic effects on native plants compared to their native congeners.