Potential phytotoxic and shading effects of invasive Fallopia (Polygonaceae) taxa on the germination of native dominant species

Abstract

Citation: Moravcová L, Pyšek P, Jarošík V, Zákravský P (2011) Potential phytotoxic and shading effects of invasive Fallopia (Polygonaceae) taxa on the germination of native dominant species. NeoBiota 9: 31-47. doi: 10.3897/neobiota.9.1266 Abstract Two species of the genus Fallopia (F. sachalinensis, F. japonica, Polygonaceae) native to Asia, and their hy brid (F. ×bohemica), belong to the most noxious plant invaders in Europe. They impact highly on invaded plant communities, resulting in extremely poor native species richness. The low number of native species in invaded communities points to the possible existence of mechanisms suppressing their germination. In this study we assessed, under laboratory conditions, whether there are phytotoxic effects of the three Fallopia congeners on seed germination of three target species: two native species commonly growing in habi tats that are often invaded by Fallopia taxa (Urtica dioica, Calamagrostis epigejos), and Lepidium sativum, a species commonly used in allelopathic bioassays as a control. Since Fallopia taxa form dense stands with high cover, we included varying light conditions as an additional factor, to simulate the effects of shading by leaf canopy on germination. The effects of aqueous extracts (2.5%, 5.0%, and 0% as a control) from dry leaves and rhizomes of the Fallopia congeners on germination of the target species were thus studied under two light regimes, simulating full daylight (white light) and light filtered through canopy (green light), and in dark as a control regime. Rhizome extracts did not affect germination. Light treatments yielded inconclusive results, indicating that poor germination and establishment of species in invaded stands is unlikely to be caused by shading alone. However, we found a pronounced phytotoxic effect of leaf extracts of Fallopia taxa, more so at 5.0% than 2.5% extract concentration. NeoBiotaLenka Moravcová et al. / NeoBiota 9: 31-47 (2011) 32 exerted the largest negative effect on the germination of Urtica dioica, F. ×bohemica on that of C. epigejos, and F. japonica had invariably the lowest inhibitory effect on all test species. The weak phytotoxic effect of F. japonica corresponds to the results of previous studies that found this species to be generally a weaker competitor than its two congeners. Although these results do not necessarily provide direct evidence for allelopathic effects in the field, we demonstrate the potential phytotoxic effect of invasive Fallopia taxa on the germination of native species. This suggests that allelopathy may play a role in the impact of Fallopia invasion on species diversity of invaded communities.

The influence of invasive Fallopia taxa on resident plant species in two river valleys (southern Poland)

“…Previous studies confirming the possibility of the sexual reproduction (also, indirectly, through the genetic variability found in F. ×bohemica), showed that the Fallopia species differ in their ecology, establishment success [27,28], response to control measures [28], genetic variation [29], and their effect on the germination and establishment of species in invaded stands [14]. A few previous studies suggested that three Fallopia taxa differed in their competitive ability.…”

“…The stand-forming habit of these species produces a dense summer canopy beneath which few other species can survive due to competition for light [14,20,21]. In addition, their rhizome system grows rampantly, producing stem litter, and the plants intensively remove nutrients from the soil, thus also taking over ground from their competitors ( [12,22,23] and the literature cited therein).…”

“…Other authors point out that allelopathy may play a role in the impact of Fallopia invasion on the species diversity of invaded communities [14,25].…”

“…Even though the invasion by Fallopia taxa is among the most intensively studied phenomena globally [14,32,33], nevertheless new aspects should be paid attention to and need explanation. More rarely undertaken studies, determining the influence of Fallopia taxa on abiotic and biotic conditions of particular habitats, devote attention to individual taxa from the Fallopia genus.…”

“…This Fallopia species complex, sometimes referred to as Japanese knotweed sensu lato, penetrates both into plant communities transformed by humans, and into natural communities, including those of alluvial plains (e.g. [9][10][11][12][13][14]), and the taxa are simultaneously a remarkable example of transformer species [15].…”