Combined allelopathy of Canada goldenrod and horseweed on the seed germination and seedling growth performance of lettuce

Abstract

The allelopathy on the seed germination and seedling growth performance (SgeSgrPe) of indigenous plant species (IPS) are considered as the main fact of the successful colonization of multiple invaders. The co-invasion of two invaders is common in some natural ecosystems. Thus, it is essential to assess the combined allelopathy of two invaders on SgeSgrPe of IPS to address the mechanisms driving the successful colonization. This study objects to assess the independent and combined allelopathy of two notorious invaders Canada goldenrod (Solidago canadensis L.) and horseweed [Conyza canadensis (L.) Cronq.] (using leaf extracts) on SgeSgrPe of the IPS lettuce (Lactuca sativa L.) via the incubation experiment in Petri dishes. Specifically, the independent and combined allelopathy of Canada goldenrod and horseweed leaf extracts on most of the seedling growth parameters of lettuce enhanced with the growing concentration of leaf extracts. The independent Canada goldenrod leaf extracts motivate greater allelopathy on most of SgeSgrPe parameters of lettuce compared to the independent horseweed leaf extracts at the same concentration. Consequently, the allelopathy on IPS may act a more prominent role in the successful colonization posed by Canada goldenrod than horseweed supposedly. The combined Canada goldenrod and horseweed leaf extracts trigger significantly higher allelopathy on most of seedling growth parameters of lettuce than the independent horseweed leaf extracts but pose significantly lower allelopathy than the independent Canada goldenrod leaf extracts at the same concentration. Thus, an antagonistic effect of allelopathy could occur after the co-invasions of the two invaders in some ecosystems, especially on the seedling growth of IPS. This implies that the allelopathy of Canada goldenrod and horseweed on the seedling growth of IPS may play a more prominent role in their single invasion process (particularly for Canada goldenrod) than in their co-invasion.