Comparison of the allelopathic effects and uptake of Fallopia japonica phytochemicals by Raphanus sativus

Fallopia japonica (Japanese Knotweed) is a prolific invader possessing several potentially allelopathic chemicals. The aim of this study was to determine whether four of these compounds inhibit the germination and growth of radish (Raphanus sativus) seedlings. Seeds were planted in potting soil and grown under glasshouse conditions for 2 weeks and the phytochemicals were gradually added to the soil over the course of the study. For all phytochemicals, there was no significant reduction in germination, plant heights, leaf widths or leaf lengths. However, plants treated with resveratrol, emodin and (–)‐epicatechin had significantly shorter root lengths than the control. Seedlings were dried and extracts were prepared with methanol. Extracts were tested via fluorescence spectrophotometry for uptake of the chemicals. Polydatin was detected at the highest concentration, with resveratrol and emodin detected at much lower concentrations. (–)‐Epicatechin was below the limits of detection. These results suggest that F. japonica may negatively impact the growth of other species and that multiple chemicals work together to give the plant a competitive advantage.