Much of the work regarding earthworm effects on other organisms has focused on the functional significance of microbial-earthworm interactions, and little is known on the effects of earthworms on microfloral and faunal diversity. Earthworms can affect soil microflora and fauna populations directly and indirectly by three main mechanisms: (1) comminution, burrowing and casting; (2) grazing; (3) dispersal. These activities change the soil's physico-chemical and biological status and may cause drastic shifts in the density, diversity, structure and activity of microbial and faunal communities within the drilosphere. Certain organisms and species may be enhanced, reduced or not be affected at all depending on their ability to adapt to the particular conditions of different earthworm drilospheres. A large host of factors (including CaCO3, enzymes, mucus and antimicrobial substances) influence the ability of preferentially or randomly ingested organisms to survive (or not) passage through the earthworm gut, and their resultant capacity to recover and proliferate (or not) in earthworm casts. Small organisms, particularly microflora and microfauna, with limited ability to move within the soil, may benefit from the (comparatively) long ranging movements of earthworms. Microflora and smaller fauna appear to be particularly sensitive to earthworm activities, and priming effects enhancing nutrient release, particularly in casts, are common. Larger fauna such as microarthropods, enchytraeids and Isopods may be enhanced under some conditions (e.g., in earthworm middens), but in other cases earthworm activity may lead to a decrease in their populations due to competition for food (microbes and organic materials), and spatial and temporal changes in food abundance. Nevertheless, considering the presently available data, the beneficial interactions of earthworms and microflora and fauna appear to far outweigh the potential negative effects. However, much is still unknown regarding the interactions of earthworms of different ecological categories on the diversity and function of microfloral and faunal communities, and much more interdisciplinary research is needed to assess the potential role of earthworms in regulating the diversity of microflora and fauna in soil systems and the potentially beneficial or harmful effects this regulation may have on ecosystem function and plant growth in different ecosystems.

How do earthworms affect microfloral and faunal community diversity

The sensitivity towards metal pollution of some population and community characteristics in Collembola was demonstrated based on observations at eight field sites along a transect from a brass mill. Samples were collected in coniferous forest soils at Gusum, southeastern Sweden, where a local brass mill has created a metal gradient in the surrounding area, with Cu and Zn concentrations in the mor (Oa + Oe) layer close to the mill at levels 50 times above background. Cu concentrations in whole animals increased exponentially in the vicinity of the smelter, but accumulation in body tissues was only observed at background sites. Neither species number, density, nor species diversity were linearly correlated with metal concentrations but instead showed a bell-shaped distribution. The vertical distribution of Collembola was clearly dependent on soil metal concentrations, and their densities at 2 – 10 cm depth were positively correlated with metal concentrations at 0–2 cm depth. The most pertinent information w...

The Gusum case: a brass mill and the distribution of soil Collembola

Regular field estimates of earthworm populations were made for two consecutive years in two fields of an experimental farm in the “Noord Oost Polder” in The Netherlands. The fields represent different agricultural management systems: conventional management and “integrated” management (i.e. reduced cultivation and lower inputs of inorganic fertilizers and biocides as compared with conventional management). Practically no earthworms were present in the conventionally managed field. In the “integrated” field, however, earthworms were observed on almost all occasions. Three species of earthworms were found, namely Aporrectodea caliginosa, Lumbricus rubellus and A. rosea . During the sampling period numbers ranged between 0 and 400 individuals m −2 , representing a biomass of 0–100 g fresh biomass m −2 . Tillage (rotary hoeing) reduced populations by > 50%, but under favorable food and weather conditions populations recovered within 5 months. A. caliginosa and L. rubellus showed different life strategies: the former migrated to deeper layers to survive winter cold, the latter survived frost periods as cocoons. Potential influences of earthworms on soil structure are the protection of the soil surface to slaking by the production of stable casts, and the perforation of deeper soil layers and plough pans, opening up the subsurface soil for plant roots. However, in the integrated system used in this study, cast were buried in the soil at the time they were needed most on the surface. Perforation of deeper layers occurred mainly when populations were high, which was in autumn. Early in the season, presence of earthworms could not prevent ponding during heavy rainfall.

Population dynamics of earthworms in a silt loam soil under conventional and “integrated” arable farming during two years with different weather patterns

https://www.ucm.es/data/cont/media/www/pag-26131/Entomopathgenic_nematode.pdf

Phoresy of the entomopathogenic nematode Steinernema feltiae by the earthworm Eisenia fetida.

The first observations of the detrimental effects of atmospheric pollution, including acidic deposition, on plants and other organisms were made in Europe more than 300 yr ago. However, scientific research into these effects did not begin until 1852, when Robert Smith, an English chemist, described the rain chemistry in the vicinity of Manchester, England. This study and other work that contributed to our understanding of the historical development of scientific knowledge and public concern over acidifying compounds in precipitation have been reviewed by Cowling (1982).

S. Rundgren

Papers

Nematode infestation and hatching failure of lumbricid cocoons in acidified and polluted soils