Allelopathic effects on the seed germination and seedling development of co-occurring native plant species (natives hereafter) are regarded as an important driver facilitating invasion of many invasive plant species (invaders hereafter). The release of silver nanoparticles (AgNPs) into the environment may affect the allelopathic effects of the invaders on the seed germination and seedling development of natives. This study aims to assess the allelopathic effects (using leaf extracts) of Canada goldenrod (Solidago canadensis L.) on the seed germination and seedling development of native lettuce (Lactuca sativa L.) treated with AgNPs with different particle sizes. Canada goldenrod leaf extracts with high concentration exhibit stronger allelopathic effects on the seedling height and root length of lettuce than those treated with low concentration. AgNPs of all particle sizes significantly decreased seed germination and seedling development indices of lettuce. AgNPs with larger particle sizes exerted stronger toxicity on leaf length and width of lettuce than those with smaller particle sizes. Thus, nanoparticles with larger particle sizes might mediate the production of increased sizes of cell wall pore size and large absorption of such substances by plant roots can be harmful. AgNPs significantly enhanced the allelopathic effects of Canada goldenrod on the seed germination and seedling development of lettuce. Small particle size AgNPs may play a more essential role in the enhanced allelopathic effects of low concentrations of Canada goldenrod leaf extracts; however, large particle size AgNPs may play a more important role in the enhanced allelopathic effects of high concentrations of Canada goldenrod leaf extracts.
Keywords: Allelopathic effects; Invasive plant species; Particle size; Seed germination and seedling development; Silver nanoparticles; Solidago canadensis.