Ergänzende Informationen zu Publikationen von Regina Ruckli

Understanding how invasive plants modify symbiotic interactions between ectomycorrhizal (EM) fungi and native host trees is a central goal in invasion biology. We examined the effect of the annual invasive plant Impatiens glandulifera on the EM association and performance of Fagus sylvatica saplings in a controlled field experiment at three sites in a deciduous forest in Switzerland. A total of 1188 one-year-old F. sylvatica saplings were planted either in plots invaded by I. glandulifera, in plots from which the invasive plant had been manually removed or in plots which were not yet colonized by the invasive plant. The 54 (3 × 18) plots were equally distributed over three sites. Saplings, including their full root systems were harvested after 3, 6 and 15 months. Exudates of the invasive plant were extracted from resin bags buried in the soil during the seedling, flowering and senescent stage of I. glandulifera. EM colonization on F. sylvatica saplings growing in invaded plot was 33% lower after 3 months and 66% lower after 15 months than saplings growing in plots from which I. glandulifera had been removed and in uninvaded plots. Survival and biomass of saplings were reduced by 16% and 30% after 15 months in plots invaded by I. glandulifera. Analysis of the internal transcribed spacer region of fungal rDNA (ITS) showed that the number of EM species was highly correlated with the number of EM morphotypes, indicating that the latter can be considered as a surrogate for EM species richness on roots of F. sylvatica saplings. EM morphotype richness on saplings was 32% lower after 15 months in invaded plots as compared to control plots. Chemical analysis revealed a high amount of naphthoquinones in plots with I. glandulifera suggesting that this putative allelochemical can be responsible for the reduction in both EM colonization and morphotype richness. Our findings demonstrate the negative impact of an annual invasive plant on the ectomycorrhizal symbiosis and performance of native F. sylvatica saplings.

Keywords: allelopathy - deciduous forest - disturbance - naphthoquinones - plant–soil feedback - resin bag

Exploring the effects of allelopathic plant chemicals on the growth of native vegetation is essential to understand their ecological roles and importance in exotic plant invasion. Naphthoquinones have been identified as potential growth inhibitors produced by Impatiens glandulifera, an exotic annual plant that recently invaded temperate forests in Europe. However, naphthoquinone release and inhibitory potential have not been examined. We quantified the naphthoquinone content in cotyledons, leaves, stems, and roots from plants of different ages of both the invasive I. glandulifera and native Impatiens noli-tangere as well as in soil extracts and rainwater rinsed from leaves of either plant species by using ultra-high pressure liquid chromatography-mass spectrometry (UHPLC-MS). We identified the compound 2-methoxy-1,4-naphthoquinone (2-MNQ) exclusively in plant organs of I. glandulifera, in resin bags buried into the soil of patches invaded by I. glandulifera, and in rainwater rinsed from its leaves. This indicates that 2-MNQ is released from the roots of I. glandulifera and leached from its leaves by rain. Specific bioassays using aqueous shoot and root extracts revealed a strong inhibitory effect on the germination of two native forest herbs and on the mycelium growth of three ectomycorrhiza fungi. These findings suggest that the release of 2-MNQ may contribute to the invasion success of I. glandulifera and support the novel weapons hypothesis.

Keywords: Impatiens glandulifera - chemical defence - 2-methoxy-1,4-naphthoquinone - ectomycorrhiza - invasion

Invasive species can have far-reaching impacts on ecosystems. Invasive plants may be able to change habitat structure and quality. We conducted a field experiment to examine whether the invasive plant Impatiens glandulifera affects native terrestrial gastropods. We also evaluated whether the invasive plant alters forest soil characteristics and microclimate which in turn may influence gastropod abundance. We sampled gastropods in plots installed in patches of I. glandulifera, in plots in which I. glandulifera was regularly removed by hand, and in control plots which were not yet colonized by the invasive plant. The three types of plots were equally distributed over three mixed deciduous forest areas that were slightly, moderately or heavily affected by a wind throw 11 years ago. A total of 33 gastropod species were recorded. Gastropod species richness was not affected by delayed effects of the wind throw, but it was significantly higher in invaded plots than in uninvaded plots. Similarly, gastropod abundance was higher in invaded plots than in the two types of control plots. Canonical correspondence analysis revealed marginally significant shifts of gastropod communities between the three types of plots and indicated that soil moisture, presence of I. glandulifera and cover of woody debris affected gastropod species composition. Field measurements showed that soil moisture was higher and daily soil temperature was more damped in patches of I. glandulifera than in the native ground vegetation. The changed microclimatic conditions may favour certain gastropod species. In particular, ubiquitous species and species with a high inundation tolerance increased in abundance in plots invaded by I. glandulifera. Our field experiment demonstrated that an invasive plant can indirectly affect native organisms by changing soil characteristics and microclimate.

Keywords: biodiversity - deciduous forests - ecosystem change - exotic plant - disturbance - gastropod community