24 Jan 2023
24 Jan 2023
Status: this preprint is open for discussion.

Earthworm-invaded boreal forest soils harbour distinct microbial communities

Justine Lejoly1,a, Sylvie Quideau1, Jérôme Laganière2, Justine Karst1, Christine Martineau2, Mathew Swallow3, Charlotte Norris4, and Abdul Samad2 Justine Lejoly et al.
  • 1Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada
  • 2Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, Québec City, Québec, Canada
  • 3Department of Earth and Environmental Sciences, Mount Royal University, Calgary, Alberta, Canada
  • 4Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, British Columbia, Canada
  • acurrent address: Department of Terrestrial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, the Netherlands

Abstract. Earthworm invasion in North American forests has the potential to greatly impact soil microbial communities by altering soil physicochemical properties, including structure, pH, nutrient availability, and soil organic matter (SOM) dynamics. While most research on the topic has been carried out in northern temperate forests, little is known on the impact of invasive earthworms on soil microbial communities in the boreal forest, a region characterized by a slower decay of organic matter (OM). Earthworm activities can increase OM mineralization, altering nutrient cycling and biological activity in a biome where low carbon (C) and nitrogen (N) availability is typically limiting microbial and plant growth. Here, we characterized and compared microbial communities of earthworm-invaded and non-invaded soils in previously described sites across three major soil types found in the Canadian boreal forest using a space-for-time approach. Microbial communities of forest floors and surface mineral soils were characterized using phospholipid fatty acid (PLFA) analysis and metabarcoding of the 16S rRNA gene, for bacteria and archaea, and ITS2 region for fungi. In forest floors, the effects of earthworm invasion were minor. In mineral soil horizons, earthworm invasion was associated with higher fungal biomass and greater relative abundance of ectomycorrhizal fungi. Oligotrophic bacteria (Acidobacteriota and Chloroflexi) were less abundant in invaded mineral soils, where Gram(+) : Gram(−) ratios were also lower, while the opposite was observed for the copiotrophic Bacteroidota. Additionally, earthworm-invaded mineral soils harboured higher fungal and bacterial species diversity and richness. Considering the important role of soil microbial communities for ecosystem functioning, such earthworm-induced shifts in their community composition are likely to impact nutrient cycling, as well as vegetation development and forest productivity at a large scale as the invasion progresses in these boreal systems.

Justine Lejoly et al.

Status: open (until 07 Mar 2023)

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Justine Lejoly et al.


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Short summary
Earthworm invasion in North American forests can alter soil functioning. We investigated how the presence of invasive earthworms affected microbial communities, key drivers of soil biogeochemistry, across the major soil types present in the Canadian boreal forest, a region largely understudied. Although total microbial biomass did not change, community composition shifted in earthworm-invaded mineral soils, where we also found higher fungal biomass and greater microbial species diversity.