The allelopathy of horseweed with different invasion degrees in three provinces along the Yangtze River in China

The effect of allelopathy from invasive alien plants (IAPs) on native species is one of the main factors for their adaptation and diffusion. IAPs can have different degrees of invasion under natural succession and are distributed in numerous regions. Seed germination and seedling growth (SGe-SGr) play a crucial role in population recruitment. Thus, it is critical to illustrate the differences in the allelopathy caused by an IAP with different degrees of invasion in numerous regions on SGe-SGr of native species to describe the primary force behind their adaptation and diffusion. This study assessed the allelopathy of the notorious IAP horseweed (Conyza canadensis (L.) Cronq.) on SGe-SGr of the native lettuce species (Lactuca sativa L.) under different degrees of invasion (light degree of invasion and heavy degree of invasion) in three provinces (Jiangsu, Anhui, and Hubei) along the Yangtze River in China. The allelopathy of horseweed leaf extract on lettuce SGe-SGr remarkably increased with the increased degree of invasion, which may be due to the buildup of allelochemicals generated by horseweed with a heavy degree of invasion compared with a light degree of invasion. A high concentration of horseweed leaf extract resulted in noticeably stronger allelopathy on lettuce SGe-SGr compared to the extract with a low concentration. There are noticeable differences in the allelopathy of the extract of horseweed leaves from different provinces on lettuce SGe-SGr with the following order i.e. Jiangsu > Hubei > Anhui. This may be due to the high latitudes for the three sampling sites in Jiangsu compared with the latitudes for the collection sites in Hubei and Anhui. There are certain differences in the environments among the three provinces. Thus, the allelopathy of horseweed on SGe-SGr of lettuce may have a greater negative impact in Jiangsu compared to the other two provinces.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12298-021-00962-y.