Allelopathic Potential of Newly Emerged Invasive Plant Cirsium vulgare (Asteraceae) in Yunnan Province of China

Cirsium vulgare (Asteraceae) is a newly emerged invasive species in Yunnan Province, China, and its phytotoxic potential has not yet been studied. This study was conducted to explore potential allelopathic effects of C. vulgare and to identify its flavonoid and phenolic acid compounds. Four aqueous extracts (roots, stems, leaves, and flower/fruit heads) of C. vulgare exhibited high inhibitory activity against the germination and seedling growth of Bidens pilosa and Digitaria sanguinalis. The inhibition rates of germination rate, germination index, root length, shoot length, and biomass of both species increased significantly with increasing concentrations, with B. pilosa being more inhibited than D. sanguinalis. Extracts from leaves and flower/fruit heads yielded the strongest inhibition, followed by stem extracts, with the lowest impact from root extracts. Flavonoids (65.41%) and phenolic acids (23.1%) collectively comprised 88.51% of all identified compounds. Thirty-eight flavonoid compounds and thirty phenolic acid compounds were selected for further analysis, representing 53.97% and 71.91% of the total content of flavonoids and phenolic acids, respectively. Many of the flavonoids and phenolic acids identified have been previously reported as known allelochemicals with possible allelopathic effects. This was the first study to show that the allelopathic potential of C. vulgare may aid its invasion and expansion.