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What would the world look like without earthworms?

The lives of soil animals are normally hidden from us. Many of us can't even imagine the diverse and numerous fauna that lives under our feet. For example, do you know what is the main contribution of earthworms, termites, millipedes, and others like them? That's right, they’re the decomposers (saprophages). And without soil invertebrates, would the surface of the Earth be probably still largely covered in the organic litter? That's possible, too. This is shown by brand new findings brought to light by a large-scale review involving an international team of authors from the Institute for the Environment of the Faculty of Science of Charles University (Dr. Petr Heděnec, Dr. Jabbar Moradi, Prof. Jan Frouz, and Prof. Pavel Kindlmann). The paper, published in the journal Scientific Reports, is the first study ever to quantify the influence of different invertebrate groups on the processing of litter on a global scale.

The authors' work consisted of analyzing a huge amount of results from already published studies - for example, they provided a global estimate of the biomass of soil fauna across different biomes based on more than 1000 existing results. More than 200 measurements in turn contributed to the determination of consumption by soil fauna. Even with other studies, results from more than 2000 observations are included in the review overall. So, what has emerged from such an extensive data analysis?

The common earthworm (Lumbricus terrestris)
Source: Wikipedia, Author: S.Sphepherd

For example, the researchers showed that the total biomass of soil fauna varies substantially between biomes. It depends mainly on differences in climate, soil type, or the ratio of carbon and nitrogen in the soil. The literature review also showed the most extensive representation of soil fauna in temperate grasslands. According to the review, the biomass decreases from temperate to desert biomes as follows: boreal forest > temperate forest > tropical grassland > tundra > tropical forest > Mediterranean ecosystems > desert and semi-desert biomes. Can you guess which representative of soil invertebrates is most abundant in the Czech Republic? If you answered earthworm, you are correct. The study showed its highest abundance in temperate forest soils, with omnivores dominating grassy areas and termites in tropical areas. The main finding is the overall estimate of annual precipitation biomass consumption by invertebrates - across biomes, it's about 50 %. In deserts, precipitation decomposition by invertebrates may be only around 14 %, while in temperate grasslands it may reach more than 100 %.

Soil invertebrates are important not only for the conversion of soil organic matter and nutrient recycling. Despite their small size, they may also contribute to water retention in the landscape, nutrient storage, or the formation of soil aggregates. Some soil fauna also influences decomposition in ways other than direct consumption - for example, by indirectly disturbing the soil structure, they contribute to the easy colonization of fallout by soil micro-organisms such as bacteria and fungi. And not just the familiar earthworms, but also protists, nematodes, insect larvae, and many others are an inconspicuous but important part of the soil fauna. The results of this paper clearly demonstrate how important the soil fauna is, even though it may often be overlooked, and its influence may seem negligible to us. An important result, in addition to the percentage of annual precipitation processing, is how much the mechanism of saprophage functioning varies between climatic zones.

Heděnec, P., Jiménez, J.J., Moradi, J. et al. Global distribution of soil fauna functional groups and their estimated litter consumption across biomes. Sci Rep 12, 17362 (2022)

Tereza Žirovnická

Published: Nov 26, 2022 09:00 PM

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