The anthropogenic spread of exotic ecosystem engineers profoundly impacts native ecosystems. Exotic earthworms were shown to alter plant community composition of the understory of deciduous forests previously devoid of earthworms. We investigated the effect of two exotic earthworm species (Lumbricus terrestris L. and Octolasion tyrtaeum Savigny) belonging to different ecological groups (anecic and endogeic) on the emergence of plants from the seed bank of a northern North American deciduous forest using the seedling emergence method. We hypothesized that (1) exotic earthworms change the seedling emergence from the plant seed bank, (2) L. terrestris increases the emergence of plant seedlings of the deeper soil layer but decreases that of the upper soil layer due to plant seed burial, and (3) O. tyrtaeum decreases plant seedling emergence due the damage of plant seeds. Indeed, exotic earthworms altered the emergence of plant seedlings from the seed bank and the functional composition of the established plant seedlings. Surprisingly, although L. terrestris only marginally affected seedling emergence, O. tyrtaeum changed the emergence of native plant species from the seed bank considerably. In particular, the number of emerging grass and herb seedlings were increased in the presence of O. tyrtaeum in both soil layers. Moreover, the impacts of earthworms depended on the identity of plant functional groups; herb species benefited, whereas legumes suffered from the presence of exotic earthworms. The results highlight the strong effect of invasive belowground ecosystem engineers on aboveground ecosystem characteristics and suggest fundamental changes of ecosystems by humanspread earthworm species.

Invasions of non‐indigenous species into natural communities are currently rated as one of the most important threats to biodiversity. Particularly exotic ecosystem engineers such as earthworms potentially have profound impacts on community assembly and functioning. We investigated the impact of invasion by the lumbricid earthworms into an aspen forest of the Canadian Rocky Mountains on soil organic matter, microorganisms and microarthropod communities. Building on the results of previous studies in this forest, we expected positive effects of Lumbricus terrestris middens and negative effects of Octolasion tyrtaeum on soil biota (increase and decrease in soil nutrient concentrations, microbial parameters and soil microarthropod density and diversity, respectively). Further, we expected that earthworm effects change with time. Combined results of previous and the present study suggest a wavelike colonization pattern for Dendrobaena octaedra and O. tyrtaeum and that indeed the impact of earthworms on soil biota changed with time, likely due to changes in earthworm density. Unexpectedly, L. terrestris middens neither affected soil abiotic nor soil biotic properties. By contrast and in contrast to our hypothesis, carbon and nitrogen concentration and C‐to‐N ratio in deeper soil layers increased in presence of O. tyrtaeum, thereby likely enhancing nutrient availability for soil microorganisms and microarthropods. Even though the density of this endogeic species was rather low, presence of O. tyrtaeum resulted in increased densities of a number of microarthropod taxa and increased microarthropod diversity. The results suggest that at low density, invasive ecosystem engineers, such as O. tyrtaeum, cause disturbances of intermediate strength thereby beneficially affecting soil microorganisms and most microarthropods. This contrasts earlier effects during the wavelike invasion of O. tyrtaeum into the aspen forest when densities of O. tyrtaeum were high resulting in generally detrimental effects on soil biota. The results emphasize the nonlinearity of earthworm effects on abiotic and biotic soil properties and call for further long‐term investigations.

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Nowadays, molecular analyses play an important role in studies of soil dwelling animals, for example in taxonomy, phylogeography or food web analyses. The quality of the DNA, used for later molecular analyses, is an important factor and depends on collection and preservation of samples prior to DNA extraction. Ideally, DNA samples are frozen immediately upon collection, but if samples are collected in the field, suitable preservation methods might be limited due to unavailability of resources or remote field sites. Moreover, shipping samples over long distances can cause loss of DNA quality e.g. by thawing or leaking of preservation liquid. In this study we use earthworms, a key organism in soil research, to compare three different DNA preservation methods – freezing at −20 °C, storing in 75% ethanol, and freeze drying. Samples were shipped from the United States of America to Austria. The DNA of the samples was extracted using two different extraction methods, peqGOLD™ and Chelex® 100. The DNA amplification success was determined by amplifying four DNA fragments of different length. The PCR amplification success is significantly influenced by preservation method and extraction method and differed significantly depending on the length of the DNA fragment. Freeze drying samples was the best preservation method when samples were extracted using the silica based extraction method peqGOLD™. For samples that were extracted with Chelex® 100, storage in ethanol was the best preservation method. However, the overall amplification success was significantly lower for the extraction procedure based on Chelex® 100. The detection of the small DNA fragments was higher and independent from the extraction method, while the amplification success was significantly reduced for the longer DNA fragments.We recommend freeze drying of DNA samples, especially when they have to be shipped for longer distances. No special packaging or declaration is needed for freeze dried samples, and the risk of thawing is excluded. Storage of freeze dried samples also reduces costs because samples can be kept at room temperature in a desiccator. It should be noted, that the extraction methods showed significant differences in DNA amplification success. Thus, the extraction method should be taken into account when choosing the preservation method.