Species-specific effects of Asian and European earthworms on microbial communities in Mid-Atlantic deciduous forests

Authors: CHANG, CHIH-HAN - Johns Hopkins University; SZLAVECZ, KATALIN - Johns Hopkins University; Buyer, Jeffrey

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: Earthworms play important roles in soil ecology, decomposing surface litter, moving organic matter from the surface down into the soil, digesting and decomposing soil organic matter, and creating tunnels that alter soil porosity. Both European and Asian species have invaded North American ecosystems. Different species and different combinations of species are shown to affect soil microbial biomass and soil microbial community composition differentially in a deciduous forest. These species-specific effects and interactions have the potential to alter soil microbial community function, increase carbon mineralization and soil respiration, and reduce carbon sequestration. These results will be useful to soil ecologists and may lead to strategies for managing earthworms and other soil biota to increase soil carbon storage.

Technical Abstract: Earthworm species with different feeding, burrowing, and/or casting behaviors can lead to distinct microbial communities through complex direct and indirect processes. European earthworm invasion into temperate deciduous forests in North America has been shown to alter microbial biomass in the soil and reduce the fungi-to-bacteria ratios. It is unclear how changes in earthworm species composition due to interspecific competition may alter this dynamics, especially under the ongoing invasion by Asian Amynthas and Metaphire species. Furthermore, it is also poorly understood how interspecific interactions involving different species may have species-dependent, non-additive effects on different groups of soil microorganisms. By conducting a two-year field mesocosm experiment in a temperate deciduous forest in the Mid-Atlantic, we examined how the Asian species Amynthas agrestis and Amynthas corticis, the European species Lumbricus rubellus and Octolasion lacteum, and their interactions affect soil microbial communities, and tested the hypotheses that the Asian species negatively affect bacteria biomass, while the interaction between the two European species has a positive effect on anaerobic microorganisms. We showed that while A. corticis generally had no effect on soil microorganisms, A. agrestis had a positive effect on microbial biomass, primarily by increasing the biomass of Gram-positive and Gram-negative bacteria. Consistent with our hypothesis, the interaction between L. rubellus and O. lacteum had a positive effect on anaerobic microorganisms, presumably through increasing anaerobic microsites in the soil. Moreover, in surface soils their interaction also negatively affected bacteria biomass. We concluded that the ongoing invasion of the Asian earthworm A. agrestis in forest soils and potential displacement of L. rubellus due to interspecific competition will lead to increased bacteria biomass and decreased biomass of anaerobic microorganisms through increasing resource availability and disrupting the interaction between L. rubellus and O. lacteum, potentially causing increased carbon mineralization and reducing soil carbon storage.