The success of invasive plants might be facilitated by allelopathy (novel weapon hypothesis) and a strong competitive effect. The invasive Impatiens glandulifera produces 2-Methoxy-1,4-naphthoquinone (2-MNQ) and can suppress the growth of natives. To date it is not known,if really 2-MNQ is responsible for the growth suppression, if this effect depends on the plant’s developmental stage and if I. glandulifera is tolerant to its own chemical weapons.
Material and Methods
We investigated the impact of I. glandulifera on seedlings and juvenile plants of Urtica dioica, Geum urbanum and Filipendula ulmaria, native species often co-occurring with I. glandulifera. Germinated seeds of this species were grown for six days on agar together with seeds of I. glandulifera or on agar containing 2-MNQ or I. glandulifera leaf material. Juveniles were investigated in a pot experiment. Four week old plants were grown for ten weeks together with I. glandulifera, together with plants of the own species or as single plant watered with 2-MNQ.
The impact of I. glandulifera was stronger on juveniles than on seedlings and it depended on the target species. I. glandulifera juveniles were surprisingly not tolerant to 2-MNQ and to intraspecific competition, which may regulate growth within I. glandulifera populations. Regarding the native seedlings 2-MNQ had a low inhibitory effect contrarily to I. glandulifera leaf material. In the juvenile stage the growth of all natives was reduced in competition with I. glandulifera, most of all U. dioica up to 86 %. However the competitive effect of I. glandulifera mostly was similar than the intraspecific competition.
In conclusion I. glandulifera has an allelopathic and a competitive effect on native plants without eliminating them but reducing their cover. Thereby 2-MNQ should not be not the only responsible allelochemical. Species specific reactions to I. glandulifera further may result in changed species compositions in native plant communities.