Allelopathy of three Compositae invasive alien species on indigenous Lactuca sativa L. enhanced under Cu and Pb pollution

[Display omitted] •C. canadensis generated stronger allelopathy than S. canadensis and E. annuus.•Allelopathy of three Compositae invasive alien species intensified under Cu and Pb.•Pb exerted stronger impacts on the allelopathy than Cu and the combined Cu and Pb. This study aims to assess the allelopathy of three Compositae invasive alien species (IAS) (i.e., Solidago canadensis L., Erigeron annuus (L.) Pers., and Conyza canadensis L. Cronq.; using their leaf extracts) on seed germination and seedling growth (SGerSGro) of indigenous Lactuca sativa L. under the pollution condition with different types of heavy metals (HMs) (including the independent Cu, the independent Pb, and the combined Cu and Pb). The allelopathy of C. canadensis on seed germination of L. sativa may play a more vital role in its outstanding colonization than that of S. canadensis and E. annuus. The allelopathy of the three Compositae IAS on SGerSGro of L. sativa intensified under the pollution condition with HMs and increased with increasing HMs concentrations. The independent Pb exerted stronger impacts on the allelopathy of the three Compositae IAS (particular S. canadensis) on SGerSGro of L. sativa especially on seed germination than the independent Cu and the combined Cu and Pb. Thus, the gradually increasing level of HMs (especially Pb) in the environment can promote the invasion process of the three Compositae IAS (particular S. canadensis).