Allelopathy of alien invasive plants (AIP) on plant germination performance is essential for their successful invasion. However, the allelopathy of AIP may be reformed or even strengthened under acid deposition. AIP in Asteraceae covers the uppermost number of AIP species at the family level presently in China. It is necessary to estimate the allelopathy of multiple Asteraceae AIP under acid deposition to address the mechanism driving their successful invasion, especially under acid deposition. However, research in this area is very restricted presently. This study purposes to estimate the allelopathy of four Asteraceae AIP, i.e., Conyza canadensis L. Cronq., Erigeron annuus (L.) Pers., Aster subulatus Michx., and Bidens pilosa L., on germination performance of the cultivated Asteraceae plant species Lactuca sativa L. which is sensitive to allelochemicals under acid deposition with different levels of acidity. Of the four Asteraceae AIP, C. canadensis, E. annuus, and B. pilosa create noticeable allelopathy on germination performance of L. sativa. The allelopathy of the four Asteraceae AIP decreases in the following order: E. annuus, C. canadensis, B. pilosa, and A. subulatus. Acid deposition with a low level of acidity reduces the allelopathy of C. canadensis, E. annuus, and B. pilosa. Inversely, acid deposition with a high level of acidity elevates the allelopathy of B. pilosa. The progressively growing level of acid deposition with high acidity may facilitate the invasion process of B. pilosa via the improved level of allelopathy.
