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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - ECOWORM (ECOSYSTEM RESPONSES TO EXOTIC EARTHWORM INVASION IN NORTHERN NORTH AMERICAN FORESTS)

Teaser

Summary

Earth is experiencing substantial biodiversity losses at the global scale, while both species gains and losses are occurring locally and regionally. Nonrandom changes in species distributions could profoundly influence ecosystem functions and services. However, few experimental tests have examined the influences of invasive ecosystem engineers, which can have disproportionally strong impacts on native ecosystems. Invasive earthworms are a prime example of ecosystem engineers that influence many ecosystems around the world. In particular, European earthworms invading northern North American forests may cause simultaneous species gains and losses with significant consequences for essential ecosystem processes like nutrient cycling and crucial services like carbon sequestration. Using a synthetic combination of field observations, field experiments, lab experiments, and meta-analyses, the proposed work will be the first systematic examination of earthworm effects on relationships between plant communities, soil communities, and ecosystem processes. Further, effects of a changing climate on the spread and consequences of earthworm invasion will be investigated. Meta-analyses will be used to test if earthworms cause ecosystems to become more species-poor and homogeneous in terms of community composition. Moving from local to global scale, the present proposal examines the influence of earthworm invasions on biodiversityâ€“ecosystem functioning relationships from an abovegroundâ€“belowground perspective. This approach is highly innovative as it utilizes exotic earthworms as an exciting model system that links invasion biology with trait-based community ecology, global change research, and ecosystem ecology, pioneering a new generation of biodiversityâ€“ecosystem function research.

Work performed

The project was successfully implemented by staffing the postdoc (2) and technician (1) positions during the first couple of months. One postdoc was successful in receiving own funding and already left to another university. A new person has been identified and will take over this position starting in November 2018. Kick-off meetings with collaborators (both via Skype and in person) were organized to finalize the planning of the field observation campaign and the field experiment. In work package (WP) I, soil microbial and animal communities were sampled in four different forests in the USA and Canada according to the proposed plan. The field sampling design had to be slightly modified by sampling areas with and without earthworms as other invasion states were impossible to standardize across forests. Two major field campaigns have been performed (one each in 2016 and 2017). The planned field experiment was successfully established in August of 2017 (and checked in 2018) and will be sampled in the next years according to the plans outlined in WP I and WP II. However, the field experiment could only be established in one forest due to logistical constraints. None of those changes threaten the objectives described in the proposal though.
We conducted a small workshop for the meta-analysis of exotic earthworm effects on soil food webs and biodiversity in 2016 (Ferlian et al. 2017, https://doi.org/10.1111/1365-2656.12746). In summer of 2017, we conducted a similar small workshop on the meta-analysis of exotic earthworm effects on soil chemical properties (in preparation). In WP II, we performed vegetation essays in four independent forests and phytometers (two aspen species) were sampled for herbivory rates and leaf chemical analyses. A complementary mesocosm experiment was set up recently to test exotic earthworm effects on tree leaf chemistry and herbivory (Master thesis of Tom KÃ¼nne). A meta-analysis was conducted on exotic earthworm effects on plant diversity and community composition (Craven et al. 2017, https://doi.org/10.1111/gcb.13446). In WP III, the global change experiment B4WarmED was sampled for microbial and animal analyses. Taken together with data from previous years, two papers have already been published (Schwarz et al. 2017, https://doi.org/10.1038/s41558-017-0002-z; Thakur et al. 2018, 10.1038/s41558-017-0032-6). In WP IV, collaborations with other scientists were intensified and additional funds were acquired (through the synthesis centre of iDiv, called sDiv) to perform global analyses of earthworm and soil biodiversity distribution. One first perspectives paper was already published (Phillips et al. 2017, https://doi.org/10.1038/s41559-017-0103) and further collaborative synthesis work is in preparation. Altogether, we have published 19 papers in the framework of this project so far. Three further complementary proposals were submitted that build on the present project and will help to advance it (to the ERC, the Dutch Research Foundation, and the German Research Foundation).
In general, the present project has advanced three main research foci. First, work in ECOWORM has contributed to the advancement of soil ecological theory by publishing a series of perspectives papers. Second, we have synthesized information on exotic earthworm effects on aboveground-belowground interactions in terrestrial ecosystems by exploring effects on plant communities, soil communities, and soil chemical properties. Third, we have explored how such aboveground-belowground interactions and soil communities are altered by different environmental changes.

Final results

Our first meta-analyses of invasive earthworm effects on plant and soil biodiversity go well beyond the state of the art by showing that earthworm effects increase with the functional richness (i.e., complexity) of the earthworm community. Earthworms facilitate the invasion of non-native plants and change soil communities by favoring fungal- over bacterial-dominated food webs. First unpublished results of a meta-analysis of exotic earthworm effects on soil chemical properties indicate that earthworms enhance nitrogen and carbon leaching from the soil, decrease soil water content, and increase soil pH. These substantial shifts in soil properties suggest profound changes in the functioning of invaded ecosystems. Moreover, my postdoc Olga Ferlian led two perspectives papers on the role of mycorrhizae for the functioning of terrestrial ecosystems. I led a perspectives paper on important topics of future soil ecological research.
Towards the end of the project, we will have information from our field observations and the experiment on ecosystem consequences to earthworm invasion, which will result in multiple papers. Moreover, we plan a synthesis project on the homogenization of plant communities in response to earthworm invasion. My ECOWORM team and I have, furthermore, been involved in additional synthesis projects, such as on the ecological cascades of earthworm invasion, the global distribution of native and exotic earthworms, state of the art of testing ecological theory with soil organisms, and global change effects on soil biodiversity.