INVASIVE KNOTWEED AFFECTS NATIVE PLANTS THROUGH ALLELOPATHY

Premise of study: There is increasing evidence that many plant invaders interfere with native plants through allelopathy. This allelopathic interference may be a key mechanism of plant invasiveness. One of the most aggressive current plant invaders is the clonal knotweed hybrid Fallopia x bohemica, which often forms monocultures in its introduced range. Preliminary results from laboratory studies suggest that allelopathy could play a role in this invasion. Methods: We grew experimental communities of European plants together with F. x bohemica. We used activated carbon to test for allelopathic effects, and we combined this with single or repeated removal of Fallopia shoots to examine how mechanical control can reduce the species' impact. Key results: Addition of activated carbon to the soil significantly reduced the suppressive effect of undamaged F. x bohemica on native forbs. The magnitude of this effect was similar to that of regular cutting of Fallopia shoots. Regular cutting of Fallopia shoots efficiently inhibited the growth of rhizomes, together with their apparent allelopathic effects. Conclusions: The ecological impact of F. x bohemica on native forbs is not just a result of competition for shared resources, but it also appears to have a large allelopathic component. Still, regular mechnical control successfully eliminated allelopathic effects. Therefore, allelopathy will create an additional challenge to knotweed management and ecological restoration only if the allelochemicals are found to persist in the soil. More research is needed to examine the mechanisms underlying Fallopia allelopathy, and the long-term effects of soil residues.