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Summary: Identifying the main threats to soil biodiversity is crucial as soils harbor ∼60% of global biodiversity. Many previous meta-analyses investigating the impact of different global changes (GCs) on biodiversity have omitted soil fauna or are limited by the GCs studied. We conducted a broad-scale meta-analysis focused on soil fauna communities, analyzing 3,161 effect sizes from 624 publications studying climate change, land-use intensification, pollution, nutrient enrichment, invasive species and habitat fragmentation. Land-use intensification resulted in large reductions in soil fauna communities, especially for the larger-bodied groups. Unexpectedly, pollution caused the largest negative impact on soil biodiversity - particularly worrying due to continually increasing levels of pollution and poor mechanistic understanding of impacts relative to other GCs. Not all GCs and stressors were detrimental; organic-based nutrient enrichment often resulted in positive responses. Including soil biodiversity in large-scale analyses is vital to fully understand the impact of GCs across the different realms.

Summary: Among the most important impacts of biological invasions on biodiversity is biotic homogenization, which may further compromise key ecosystem processes. However, the extent to which they homogenize functional diversity and shift dominant ecological strategies of invaded communities remains uncertain. Here, we investigated changes in plant communities in a northern North American forest in response to invasive earthworms, by examining the taxonomic and functional diversity of the plant community and soil ecosystem functions. We found that although plant taxonomic diversity did not change in response to invasive earthworms, they modified the dominance structure of plant functional groups. Invasive earthworms promoted the dominance of fast-growing plants at the expense of slow-growing ones. Moreover, earthworms decreased plant functional diversity, which coincided with changes in abiotic and biotic soil properties. Our study reveals that invasive earthworms erode multiple biodiversity facets of invaded forests, with potential cascading effects on ecosystem functioning.

Summary: Invasive earthworms colonize ecosystems around the globe. Compared to other species’ invasions, earthworm invasions have received little attention. Previous studies indicated their tremendous effects on resident soil biota representing a major part of the terrestrial biodiversity. We investigated effects of earthworm invasion on soil microbial communities in three forests in North America by conducting DNA sequencing of soil bacteria, fungi, and protists in two soil depths. Our study shows that microbial diversity was lower in highly invaded forest areas. While bacterial diversity was strongly affected compared to fungi and protists, fungal community composition and family dominance were strongly affected compared to bacteria and protists. We found most species specialized on invasion in fungi, mainly represented by saprotrophs. Comparably, few protist species, mostly bacterivorous, were specialized on invasion. As one of the first observational studies, we investigated earthworm invasion on three kingdoms showing distinct taxa- and trophic level-specific responses to earthworm invasion.