The earthworms or Lumbricidae attain the largest biomass in soil among soil invertebrates. They occur in high abundance and diversity in soils worldwide except for deserts and arctic tundra. In temperate regions average abundance and biomass is about 100 specimen per square meter, and even in intensively managed arable soils still about 50 g fresh earthworm biomass can be found per square meter though one order of magnitude less than in pasture and grassland2. Earthworms contribute to the functioning of soil ecosystems by consuming decaying plant matter, creating burrows that aerate soil and allow water to infiltrate soil; in its entirety, they contribute considerably to soil formation. Earthworms contribute to three of the four soil function models; Water Regulation and Purification, Nutrient Cycling and Carbon Sequestration and Climate Regulation, through their role in supporting the processes of aggregation, bioturbation, fragmentation and macropore formation.
The upper part of soil will have passed through the earthworm gut every tenth year and are therefore entirely coprogenic, i.e. made up of earthworm excrements and casts,. A large body of knowledge and ongoing research is centered on earthworms and this has led to acknowledgement of their crucial role. Thus, most new chemicals with a fate in soil will be tested according to ISO or OECD standards,.
Earthworms respond to land management, agriculture and chemicals in soil, so the species composition and their abundance will reflect any change in soil structure and food availability and quality. Hence, their abundance and diversity is used to calculate soil health indices.
Earthworms can be hand-sorted from soil and their enumeration and identification are highly standardized and facilitated by concise easily accessible identification keys, although some level of expert knowledge is needed for precise identification. Currently, earthworm DNA in soil, i.e. eDNA, has slowly been adopted for assessment of earthworm diversity, thus avoiding the need for taxonomic expertise for earthworm identification.
Text by Dr. Paul Henning Krogh, Department of Bioscience, Aarhus University
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