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2019 The annual invasive plant Impatiens glandulifera reduces hyphal biomass of soil fungi in deciduous forests — Gaggini L, Rusterholz H-P & Baur B — Fungal Ecology 39: 242–249 doi> 10.1016/j.funeco.2018.12.004

Soil fungi play a crucial role in ecosystem functioning and there is increasing evidence that exotic plants invading forests can affect soil fungal communities. We examined potential effects of the invasive plant Impatiens glandulifera on hyphal biomass of ectomycorrhizal fungi, their genetic diversity and the diversity of other soil fungi in deciduous forests in Switzerland. We compared invaded patches with patches where I. glandulifera had been removed, by establishing pairs of 3-m long transect lines at the edge of seven areas of either type. Along the transects we assessed the length of ectomycorrhizal fungal hyphae using the 'ingrowth mesh bag method', and used terminal restriction fragment length polymorphism (T-RFLP) analysis to examine fungal genetic diversity. The invasive plant reduced fungal hyphal biomass by 30-80%: the reduction was largest in the centre of the patch. I. glandulifera did not alter fungal richness, but affected the composition of fungal communities. This is probably the result of a decrease of mycorrhizal fungi, coupled with an increase of saprotrophic fungi. Our findings demonstrate the adverse impacts of an annual invasive plant species on both fungal hyphal biomass and the composition of soil fungal communities. This may negatively affect forest nutrient and carbon cycling, soil stability and the functionality of the fungal community, with major consequences for forest ecosystem functioning.

Keywords: biological invasions - ectomycorrhizal hyphae - extramatrical mycelium - hyphal length - ingrowth mesh bags - soil fungi - T-RFLP

2019 The invasion of an annual exotic plant species affects the above- and belowground plant diversity in deciduous forests to a different extent — Gaggini L, Rusterholz H-P & Baur B — Perspectives in Plant Ecology, Evolution and Systematics 38: 74–83 doi> 10.1016/j.ppees.2019.04.004

Invasive plant species can significantly affect native biodiversity and ecosystem functioning. Even though the majority of ecosystems have more than 50% of the plant biomass belowground, most studies investigating the effects of invasive species on plant diversity focus on the aboveground vegetation. DNA-based methods allow the determination of belowground plant structures. Using these techniques, we examined potential effects of the annual invasive plant Impatiens glandulifera on both the above- and belowground plant species richness and composition in mixed deciduous forests in Northwestern Switzerland. We established 24 plots in three forest areas invaded by I. glandulifera and in three adjacent forest areas, which were not yet invaded. In each plot, we determined plant species richness and abundance in the aboveground vegetation, and collected soil samples at depths of 0–10_cm and 11–20_cm to determine belowground plant species richness. We extracted DNA from fine roots in the soil samples and applied the FAFLP technique (fluorescent amplified fragment length polymorphism) for two different regions of the chloroplast DNA (trnL-trnF intergenic spacer and P6 loop). We established a reference library for all plant species occurring in the study areas to identify the species present in mixed-root samples. Our results showed that I. glandulifera caused shifts in both the above- and belowground plant species composition. Plant species richness was reduced by 30% aboveground in invaded plots, but not belowground in the same plots. Many geophytes and woody species were found belowground but not aboveground in invaded plots. Root biomass was reduced by 35–55% in invaded plots, most probably due to allelopathic compounds released by the invasive plant into the soil. Our field survey shows that above- and belowground plant communities respond differently to the invasion of an annual plant species, and that the invasive species can negatively affect forest ecosystem functions, by reducing root biomass and altering plant species richness and composition.

Keywords: biological invasions - fluorescent amplified fragment length polymorphism (FAFLP) - Impatiens glandulifera - mixed root samples - species identification - trnL intron

2018 The invasive plant Impatiens glandulifera affects soil fungal diversity and the bacterial community in forests — Gaggini L, Rusterholz H-P & Baur B — Applied Soil Ecology 124: 335–343 doi> 10.1016/j.apsoil.2017.11.021

Invasive plants may severely impact native biodiversity and ecosystem functioning. We examined potential effects of the invasive annual plant Impatiens glandulifera Royle on soil fungal and bacterial communities in temperate forests. Using a space-for-time approach, we established 72 plots in forest areas invaded by I. glandulifera and in forest areas, which were not yet invaded, equally distributed over three coniferous and three deciduous forests. In each plot, we determined plant species richness and abundance in the above-ground vegetation as well as the diversity and composition of the soil fungal community using T-RFLP analysis. Biolog Ecoplates were used to assess the activity of soil bacteria. The invasion of I. glandulifera caused significant shifts in plant species composition. Invaded plots were characterized by a higher diversity and an altered composition of the soil fungal community and by a lower soil bacterial activity in late spring. Carbon substrate utilization patterns of soil bacteria were also changed in invaded plots. Our experiment shows that I. glandulifera can modify soil fungal and bacterial communities, indicating an indirect effect of altered soil properties induced by the invasive plant, combined with the release of allelopathic compounds into the soil.

Keywords: annual exotic plant species - biological invasions - microbial activity - space-for-time substitution - soil fungal community

2017 Settlements are a source for the spread of non-native plants into mixed deciduous suburban forests — Gaggini L, Rusterholz H-P & Baur B — Acta Oecologia 79: 18–25 doi> 10.1016/j.actao.2016.12.008

• We conducted vegetation surveys in forests near to and far from settlements.
• Settlements are a source for the spread of non-native plants into suburban forests.
• Roads and gardens contribute to the establishment of non-native plants in forests.
Urbanization is considered as a major driver for biotic homogenization. Urbanization also promotes the dispersal of non-native species. This study examined the roles of suburban settlements and of the surrounding landscape composition for the spread of non-native plant species into adjacent mixed deciduous forests in Southern and Northwestern Switzerland. The number and abundance of native and non-native vascular plant species in both the ground vegetation and shrub layer were recorded in 15 forest sites situated adjacent to settlements and 15 control sites far from settlements. Various site and landscape characteristics were assessed in the surroundings (100 m radius) of the study sites. In both regions we found a higher number and larger abundance of non-native plant species in forest sites adjacent to settlements than in control forest sites. Furthermore, non-native plants were more frequently recorded close to roads and in sites surrounded by a large percentage cover of garden. All these effects were more pronounced in Southern Switzerland, a region with milder winter climate, than in Northwestern Switzerland. Our study showed that settlements are a source for the spread of non-native plant species into Central European suburban forests, and that the composition of the surrounding landscape matrix (e.g. traffic infrastructure, percentage cover of gardens) also affects the establishment of non-native plants.

Keywords: alien plants - deciduous forests - gardens - landscape matrix - Switzerland - urbanization