Garlic mustard (Alliaria petiolata), Amur honeysuckle (Lonicera maackii)
and lesser celandine (Ranunculus ficaria) are three invasive species in US Midwestern
forests. The comparative allelopathic effects of leaf extracts of these species on
germination and reproduction of Arabidopsis thaliana were investigated in a growth
room. Highest extract concentrations (0.3 and 0.2 g fresh leaf tissue/mL distilled
water) of L. maackii delayed germination in potting soil compared to the control.
Extracts of L. maackii also decreased the number of siliques in potting soil compared
to the control and to A. petiolata extracts, with extracts of R. ficaria having
intermediate effects. In field soil, extracts of L. maackii and R. ficaria significantly
decreased the number of siliques compared to extracts of A. petiolata. In a third
experiment, effects on germination of three agricultural species (Brassica oleracea,
Lactuca sativa and Ocimum basilicum), were studied. Ranunculus ficaria and L.
maackii extracts were least harmful to germination, while A. petiolata extracts were
most harmful. Germination of L. sativa and O. basilicum was more sensitive to A.
petiolata and R. ficaria extracts, while germination of B. oleracea was more sensitive
to L. maackii extracts. These results showed differential allelopathic effects of these
invasive species, which varied with test species and experimental conditions