Allelopathic effects and phytochemical analysis of Coleanthus subtilis as possible factors involved in its colonization success.

Coleanthus subtilis is a globally rare therophyte growing on exposed bottoms of water reservoirs and riverbanks. Despite its small size and ephemeral nature, it shows a potential to conquer new areas and can dominate phytocoenoses of small wetland therophytes and pioneer the land interface zones of lakes, pools and ponds. However, features enabling its spread and dominance in patches remain poorly understood. Also, the composition of biologically active compounds of the species has not been characterized in detail so far. Therefore, we assessed the species allelopathic potential as referred to the presence of biologically active compounds and ecotoxicity. Several natural products belonging to benzoxazinone derivatives, phenolic compounds, and carboxylic acids were identified in this species, which are likely to have allelopathic potential. The results of phytotoxic tests showed that water extract of C. subtilis induced a delay in germination of the model plant Sinapis alba, and, at concentrations higher than 4%, caused a significant reduction in the percentage of germinated seeds. In addition, root growth of S. alba was inhibited at concentrations of the extract greater than 4%. Oppositely, the growth of model plant hypocotyl was stimulated by low concentrations (< 4%) of the C. subtilis water extract. By showing the allelopathic potential, our results shed new light on the C. subtilis performance and absolute dominance in some patches of muddy vegetation.