Allelopathic effect of invasive Canadian goldenrod (Solidago canadensis L.) on early growth of red clover (Trifolium pratense L.)

Solidago canadensis belongs to highly invasive species in Europe, it is established in ruderal, semi-natural and natural communities. To test the traits related to invasiveness, the experiment with the potential of allelopathic compounds produced by the species was conducted. The aqueous extract from the goldenrod leaves was used to examine the germination and early stages of development of Trifolium pratense, the species as an example of fodder plant common in meadows and pastures. Three types of aqueous extract were used: decoction, infusion, and macerate. All extracts of Canadian goldenrod had a negative influence on the germination process of red clover, however, the effect changed in time and type of extract. The most inhibiting influence was documented for the macerate type of aqueous extract. Similarly, the negative influence of macerate was the highest for the length and weight of the seedlings, the content of chlorophyll a and b, and electrolyte leakage. As the procedure of obtaining the macerate is the most like the process of natural extraction of allelopathic substances in nature, there is the practical conclusion to remove the moved biomass of the goldenrod during the restoration process of areas colonised by the species.