Abstract:

Aims The interspecific interactions between plants are vital for species survival. For biological invaders, stronger competitive ability allows them to invade successfully when appearing with indigenous species, which is considered as an important mechanism underlying successful invasion. However, environmental changes may alter interspecific interactions, thus impacting invasion consequences. In this study, we aimed to explore the effect of acid rain, which is a seriously environmental problem worldwide, on the interactions between a Chinese invader common ragweed (Ambrosia artemisiifolia) and its accompanying indigenous forb (Bidens bipinnata) to further explore the role of an environmental disturbance in biological invasions.

Methods In March 2021, we performed a de Wit replacement competitive experiment with A. artemisiifolia and B. bipinnata at the campus of Beijing Normal University; meanwhile we also simulated acid rain through providing different concentrations of solutions (pH = 3, 4, 5, 7). Plant height after 24, 34, 45 days, final plant height, and aboveground biomass were determined for each individual plant. Relative neighbor effect (RNE) and replacement diagrams were used to estimate interspecific competition.

Important findings When the two species were planted separately, the medium level of an acid solution (pH = 4) promoted their early growth, and the high level of an acid solution (pH = 3) significantly inhibited their early growth but did not affect the final plant height. When grown together, the ragweed showed a decrease in plant height in the presence of the high level of an acid solution (pH = 3) after 34 and 45 days, but this negative effect disappeared at harvest. The plant height of bidens applied with the high level of an acid solution (pH = 3) decreased significantly at harvest compared with the control treatment. The RNE of bidens on ragweed was not significant under all the treatments, while the RNE of ragweed on bidens was significant without acid application or under the condition of acid treatments at a lower proportion of bidens. Replacement diagrams showed that the bidens had an advantage over ragweed when applied with the low level of an acid solution (pH = 5) at higher proportions, and the ragweed had an enhanced advantage over bidens when applied with the high level of an acid solution (pH = 3). Our study suggests that acid rain might affect the growth of ragweed and bidens as well as their interactions, and acid rain with low pH may boost the competitive advantage of invasive ragweed.

Key words: acid rain, interspecific competition, environmental disturbance, plant invasion, common ragweed