SEM image of Milnesium tardigradum in active state - journal

Soil mesofauna are invertebrates between 0.1mm and 2mm in size, which live in the

soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...

or in a leaf litter layer on the soil surface. Members of this group include nematodes,

mite Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear e ...

springtail Springtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects (the other two are the Protura and Diplura). Although the three orders are sometimes grouped together in a class called Ento ...

s (collembola), proturans,

pauropod Pauropods are small, pale, millipede-like arthropods. Around 830 species in twelve families are found worldwide, living in soil and leaf mold. They look rather like centipedes, or millipedes, and may be a sister group of the latter. However, this ...

s, rotifers,

earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. T ...

tardigrade Tardigrades (), known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbä ...

s, small

spiders Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species di ...

, pseudoscorpions,

opiliones The Opiliones (formerly Phalangida) are an order of arachnids colloquially known as harvestmen, harvesters, harvest spiders, or daddy longlegs. , over 6,650 species of harvestmen have been discovered worldwide, although the total number of ext ...

(harvestmen),

enchytraeidae Enchytraeidae is a family of microdrile oligochaetes. They resemble small earthworms and include both terrestrial species known as potworms that live in highly organic terrestrial environments, as well as some that are marine. The peculiar genu ...

such as potworms,

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...

e, small isopods and

myriapod Myriapods () are the members of subphylum Myriapoda, containing arthropods such as millipedes and centipedes. The group contains about 13,000 species, all of them terrestrial. The fossil record of myriapods reaches back into the late Silurian, ...

s. They play an important part in the

carbon cycle The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major componen ...

and are likely to be adversely affected by climate change. Soil mesofauna feed on a wide range of materials including other soil animals, microorganisms, animal material, live or decaying plant material, fungi, algae, lichen, spores, and pollen. Species that feed on decaying plant material open drainage and aeration channels in the soil by removing roots. Fecal material of soil mesofauna remains in channels which can be broken down by smaller animals. Soil mesofauna do not have the ability to reshape the soil and, therefore, are forced to use the existing

pore space in soil The pore space of soil contains the liquid and gas phases of soil, i.e., everything but the solid phase that contains mainly minerals of varying sizes as well as organic compounds. In order to understand porosity better a series of equations have ...

, cavities, or channels for locomotion. Soil

Macrofauna Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is ''flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. Zoo ...

, earthworms, termites, ants and some insect larvae, can make the pore spaces and hence can change the soil

porosity Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measur ...

, one aspect of soil morphology. Mesofauna contribute to habitable pore spaces and account for a small portion of total pore spaces.

Clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

soils have much smaller particles which reduce pore space. Organic material can fill small pores. Grazing of bacteria by bacterivorous nematodes and flagellates, soil mesofauna living in the pores, may considerably increase Nitrogen mineralization because the bacteria are broken down and the nitrogen is released. In agricultural soils, most of the biological activity occurs in the top , the

soil biomantle The soil biomantle can be described and defined in several ways. Most simply, the soil biomantle is the organic-rich bioturbated upper part of the soil, including the topsoil where most biota live, reproduce, die, and become assimilated. The biomant ...

or plow layer, while in non-cultivated soils, the most biological activity occurs in top of soil. The top layer is the organic horizon or O horizon, the area of accumulation of animal residues and recognizable plant material. Animal residues are higher in nitrogen than plant residues with respect to the total carbon in the residue. Some

Nitrogen fixation Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...

is caused by bacteria which consume the amino acids and sugar that are exuded by the plant roots. However, approximately 30% of nitrogen re-mineralization is contributed by soil fauna in agriculture and natural ecosystems. Macro- and mesofauna break down plant residues to release Nitrogen as part of

nutrient cycling A nutrient cycle (or ecological recycling) is the movement and exchange of inorganic and organic matter back into the production of matter. Energy flow is a unidirectional and noncyclic pathway, whereas the movement of mineral nutrients is cycli ...

References

{{reflist Soil biology Zoology