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Bohemian knotweed Reynoutria × bohemica Chrtek et Chrtková seems to be more a physical bully than a chemical weapon specialist

Globally, in addition to direct destruction of natural habitats, invasive species are considered to be the biggest threat to biodiversity. The Polygonaceae family in Croatia consists of seven genera, one of which is Reynoutria, with three taxa. Bohemian knotweed Reynoutria × bohemica Chrtek et Chrtková is a hybrid of two species, Reynoutria japonica Houtt. and Reynoutria sachalinensis (F. S. Petrop.) Nakai in T. Mori, which spontaneously developed in a new area, outside the areas of its parental species. Bohemian knotweed, like other species of the genus Reynoutria, displays a number of invasive characteristics and is considered to be expanding even more aggressively than its parental species. The key of its success could potentially lie in its allelopathic activity, which was confirmed in number of experiments conducted with the Bohemian knotweed's leaf and roots extracts in Petri dishes, testing its effect on germination and growth of various test plants. Here, we tested impact of the Bohemian knotweed on soil with respect to its alteration of some chemical properties (pH, organic matter, humus) and allelopathic potential it might have on germination and growth of two test plants, Triticum aestivum L. and Sinapis alba L. We have collected triplicate soil samples from centre of the three Bohemian knotweed stands, its edge and control samples in near proximity (overall 27 samples). After three weeks of germination (270 seeds per test species) and growth in the climate chamber (12:12 hours 2.6 klux light vs. dark, with 24 ˚C), all seedlings were weighted, scanned for measuring of their length, dried (24 hours at 80 ˚C) and weighted again. Based on ANOVA and Tukey's post-hoc test we determined that the presence of R. × bohemica did not significantly affect chemical characteristics of the soil or the growth and sprouting of Triticum aestivum L. and Sinapis alba L. based on their length, fresh, dry and dry/fresh ratio weight. Competition through early growth in the season and success in obtaining resources (light, water and nutrients) seems to be the main mechanism of invasive success of this taxa. However, this should be further tested on plant species that are actually outcompeted and supressed in nature.

allelopathy ; Croatia ; ImageJ ; invasive species ; Zagreb

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