Negative impacts and comparative allelopathic effects of Ranunculus ficaria, lesser celandine, a riparian ephmeral invasive plant

Background/Question/Methods

Ranunculus ficaria has been identified as invasive plant in the United States, despite a lack of published evidence of its negative impacts. We examined if R. ficaria negatively affected the growth and reproduction of the native Impatiens capensis and, if so, whether it is by allelopathy, nutrient competition or some combination thereof. We performed a fully-factorial field experiment, manipulating the presence of R. ficaria, nutrients, and allelopathy (with the use of activated carbon). We also performed a study in the growth room using leaf extracts to investigate the comparative allelopathic effects of R. ficaria, using two known allelopathic Midwestern species, bush honeysuckle (Lonicera maackii) and garlic mustard (Alliaria petiolata). In a fully-factorial experiment, the effect of extract species and extract concentration on reproduction of Arabidopsis thaliana was investigated. A subsequent experiment investigated the effect of these treatment solutions on germination of three agricultural species (Lactuca sativa, Brassica oleracea, and Ocimum basilicum). 

Results/Conclusions

In the field, the presence of R. ficaria tended to negatively affect survival of I. capensis. Nutrients showed a significant effect on growth and reproduction as predicted. The interaction between the presence of R. ficaria and carbon on seed production was significant. In the absence of carbon, R. ficaria significantly decreased seed production, illustrating the negative impact of R. ficaria. In the presence of carbon, there was no effect of R. ficaria, suggesting that carbon ameliorated the negative allelopathic effect of R. ficaria. In the growth room, there were significantly fewer siliques when plants in field soil were treated with extracts of L. maackii and R. ficaria compared to A. petiolata. Across all agricultural test species, R. ficaria and L. maackii extracts affected germination the least, while A. petiolata extracts affected germination the most.  However, the extracts impacted species germination differentially; L. sativa and O. basilicum were more sensitive to A. petiolata and R. ficaria extracts and B. oleracea was more sensitive to L. maackii extracts. This is one of the first studies to demonstrate the negative impact of R. ficaria in the field and the possible role of allelopathy in this species. Further, we show that the negative impacts of this ephemeral species persist well beyond its early growing season. These results also provide evidence of differential allelopathic effects of three important Midwestern invasive species, which vary depending on test species and experimental venue.