Earthworm invasions of ecosystems devoid of earthworms: effects on soil microbes

Abstract

Recent studies document NorthAmerican earthworm invasions and their profound effects on the structure of the soil profile, which is the habitat for soil microorganisms (mainly fungi and bacteria). Dramatic alterations made to these layers during earthworm invasion significantly change microbial community structure and therefore microbial activities such as C transformations. Understanding the impacts of earthworm invasion on the microbes themselves will give insight into earthworm effects on microbial activities. Bacterial and actinomycete communities in earthworm guts and casts have not been studied in environments recently invaded by earthworms. Earthworm invasion tended to decrease fungal species density and fungal species diversity and richness. The presence of earthworms decreased zygomycete species abundance probably due to disruption of fungal hyphae. Physical disruption of hyphae may also explain decreased mycorrhizal colonization rates, decreased mycorrhizal abundance and altered mycorrhizal morphology in the presence of earthworms. Mixing of organic layers into mineral soil during earthworm invasion tended to decrease microbial biomass in forest floor materials while increasing it in mineral soil. In newly invaded forest soils, microbial respiration and the metabolic quotient tended to decline. In forests where either the microbial community has had time to adapt to earthworm activities, or where the destruction of the forest floor is complete, as in invasions by the Asian Amynthas hawayanus, the presence of earthworms tends to increase the metabolic quotient indicating a shift to a smaller, more active microbial community.

Distribution and impacts of invasive earthworms in Canadian forest ecosystems

“…There have been few studies on the interaction between earthworms and mycorrhizae, and most have focussed on arbuscular mycorrhizae (McLean et al 2006). Given the overwhelming importance of ectomycorrhizae in coniferous forests and their distribution within the organic layers (e.g., Goodman and Trofymow 1998), there is an urgent need to determine if and how invasive earthworms will jeopardize this vital association between coniferous trees and their fungal partners.…”

Earthworms, stand age, and species composition interact to influence particulate organic matter chemistry during forest succession

“…A correlation crossproducts matrix, which produces correlation coefficients among the compounds, was used in the PCA. This method provides a broken stick eigenvalue; the broken-stick eigenvalue was less than the actual eigenvalue for the first and second axes; therefore these were used for interpretation (McCune and Mefford 1999). Pearson and Kendall correlations with the main matrix were calculated in PC-ORD.…”

The wave towards a new steady state: effects of earthworm invasion on soil microbial functions

“…Li et al 2002) soil microbial biomass and activity. Reviewing the previous literature on exotic earthworm effects on soil microbes, McLean et al (2006) concluded that earthworms change microbial community composition towards a smaller, but more active microbial community. They moreover hypothesized that impacts of exotic earthworms on soil microbes depend on the stage of invasion: initial decreases in soil microbial respiration and metabolic quotient may be followed by a decrease in microbial C use efficiency.…”