The combined treatments of Canada goldenrod leaf extracts and cadmium pollution confer an inhibitory effect on seed germination and seedling development of lettuce

Abstract

Increasing levels of heavy metals are released into ecosystems. The influence of heavy metal pollution on successful invasive species has raised considerable interest, particularly regarding potential allelopathic effects on seed germination and seedling development of native species. Adding heavy metals may alter or even enhance such allelopathic effects of invasive species. The aim of the present study was to address the combined treatments of the invasive species Canada goldenrod (Solidago canadensis L.) leaf extracts and cadmium (Cd) pollution on seed germination and seedling development of the homologous native species lettuce (Lactuca sativa L.). Results showed that the combined treatments of Canada goldenrod leaf extracts and Cd pollution significantly decreased seed germination and seedling development of lettuce compared with the control. In addition, the indices of allelopathic effects for all seed germination and seedling development indices of lettuce were less than zero under the combined treatments of high concentration of Canada goldenrod leaf extracts and Cd pollution (regardless of concentration). Thus, the combined treatments of high concentration of Canada goldenrod leaf extracts and Cd pollution pose an inhibitory effect on seed germination and seedling development of lettuce. Further, the combined treatments of high concentration of Canada goldenrod leaf extracts and Cd pollution (regardless of concentration) cause more toxic effects than the combined treatments of low concentration of Canada goldenrod leaf extracts and Cd pollution (regardless of concentration) on all seed germination and seedling development indices of lettuce. Thus, the inhibitory effects of Canada goldenrod on the seed germination and seedling development of co-occurring native species may be intensified at heavy invasion degrees under increased heavy metal pollution. Subsequently, the competitiveness and fitness of native species may be notably decreased via the reduced seed germination and seedling development and then the notorious invader can establish progressively-growing populations in the colonised ecosystems.