Role of soil fauna
Soil ecology focuses on the interactions and controlling factors among soil organisms. About the diversity of soil living groups our knowledge is weak. Considering their number and their biomass the most dominant groups in the soil are the microorganisms like bacteria and fungi. Soil ecosystem usually contains the diversity of animals: nematodes, enchytraeids, mites and springtails. According to their size, there are three main groups: macrofauna, mesofauna and microfauna.
Unlike macrofauna (earthworms, ants, insect larvae) the mesofauna (springtails, mites, nematodes, tardigrades etc.) has limited burrowing ability. They have to live within the soil pores and channels. In general with decreased pore volume the dominance of small soil living animals increases. The activity of microbial organisms and mesofauna is influenced by the water-air balance inside the pores. Because their lead to oxygen shortage (anaerobiosis) and water loss (dehydration), drought and saturation (waterlogging) is harmful for the soil animal communities.
The population size of the mesofauna is highest when the porosity, nutrient content of the soil is high and it has structured horizons. Most soil activity occur in the top 20 cm of soil, in case of uncultivated soil it is expressed at the upper 5 cm.
The biological active layers of the soil can be divided to several horizons. Surficial organic deposit with litter layer of plant residues in relatively non-decomposed form take place at the upper organic horizon. It is characterized by high C:N ratio. Under this there is a fermentation layer. It is consist of decomposed matter whose origin can be spotted on sight (for instance, fragments of rotting leaves). It is permeated by hyphae. The lower humus layer contains amorphous products of decomposition, the origin of which is not readily visible.
In the soil food web, mesofauna uses all trophic levels. While they feed on roots, they have direct impact on producers. They have an indirect effect as well trough decomposition and mineralisation (transform organic matter into inorganic).
The effect of plants on the soil is considerable. They have a huge impact on soil life by transporting organic matter above and belowground, by shading, protecting the soil and directly by the water and organic matter intake of their roots. Mesofauna is often concentrated around roots and organic matter which sign the possible occurrence of some kind of sources (food, shelter). According to the food source many soil animal is highly adaptable. Their strategy is wide from plant feeders to predators, but omnivory is the most prevalent. In the mesofauna according the soil biota there are 3 main groups: nematodes, springtails and mites.
Nematodes are abundant, small, organisms, with short generation time. They can respond the nutrient status of the soil really fast. They feed on plant roots, bacteria, fungi, algae or on other nematodes. The most abundant arthropods in the soil are mites and springtails, which can account for 95 % of total soil microarthropods number. There are 3 suborders of mites in the soil. The most dominants are the Oribatidae, which live mainly in the organic horizon. Large, active mites belong to the suborder Mesostigmata, whereas Prostigmata is a complex group according to their taxonomy. The latter is the most heterogeneous group according to their feeding as well. In this group we can find mostly fungivor and predator species. Springtails have a high metabolic, feeding and reproductive potential. Because springtails live on decaying plant material and associated microflora, their distribution is influenced by the hyphae and spores of the saprophytic fungi.
These groups are essential for an appropriate soil life. Despite their importance, in case of overpopulation, they can be considered as pest species as well. Abundant nematodes in agricultural ecosystem can influence the water and nutrient uptake of plants. So they change the primer production. If their main food source is absent, some other groups of the mesofauna can become a pest as well. Species from certain springtails families like Sminthuridae and Onychiuridae feed on roots too, which can contribute the transfer of infections as well.
Some soil mite groups (Tarsonemidae, Periohmanniidae) are well adapted to consume plant issues. Most of them consume plant material if it has started to decay. They can control the nematode population. Springtails can control nematodes as well but they feed on nematodes which are insect parasites. With the latter they decrease the effectiveness of biological control of pest species.
In ecosystem processes, decomposition and nutrient cycling, micro- and mesofauna contributes in complex and interactive way. Microarthorpods fragment the detritus. The enhanced surface facilitate the further microbial decomposition. Even they do not digest totally the swallowed material, they break it down, moisture it and make it available for the microorganisms.
Plants benefit from the increased N mineralization caused by microarthropod activity. The biomass and N content of the roots are higher in the presence of protozoans and nematodes. Soil fauna is responsible for the 30% of nitrogen mineralization. Smaller species help in the humus formation they feed on and mix the organic and mineral fractions of the soil. Following their death, nutrients are available for plants. They can enhance microbial colonization of organic matter by transporting fungi, protozoans and bacteria.
At moderate disturbance, biodiversity of soil fauna can be high. However considerable disturbances decrease the survivorship of the specimens, change the availability of the food and other environmental sources. In a contaminated environment, taxonomic diversity of microinvertberate fauna can be lower than in unpolluted agricultural areas. Sensitive species disappear after pollution, with this competition decreases and tolerant species become abundant.
During the “life” of the soil, opportunistic species, like bacteria and organisms feeding on them, colonise the soil. After that fungi and their consumers enter the community. Springtails and Diptera larvae are able to colonise almost bare soils as well. Next, top predators, like predaceous mites and nematodes appear. At the end macro- and megafauna: earthworms, millipedes, centipedes, slugs and sow bugs joins to the community. Succession can be interrupted by cultivation. These disturbances decrease the diversity and successional maturity.
Soil texture is crucial for the soil living organisms. Smaller animals moves between soil particles, whereas bigger species gnaw themselves trough the soil or use tunnels. Soil texture plays a considerable role in the soil fauna induced carbon and nitrogen mineralization. It is faster in coarse than in fine-textured soil. In clay and sandy soil, organic matter is protected from decomposers. In clay soil nematodes and microinvertebrates are less abundant than in sandy or peaty soils. Compaction of soil inversely affects the abundancy of soil mesofauna.
Cultivation affects the biogeochemical cycles because it alters the size of soil pores, thereby gas and water infiltration ability as well. Cultivation disrupts soil aggregates, closes soil cracks and pores and contribute to the desiccation of soil at the surface.
Mesofauna aggregates around manure and plant remains. During fertilization by manure population size of fungivore nematodes, springtails and sometimes mesostigmatid mites increase. Mineral or manure fertilizers in high dose can be harmful for the soil fauna because of the high osmotic pressure of the salts and toxicity.
According to their morphological adaptation, ecological role and in which section of their life time is spent in the soil, there are 4 main groups of soil living organisms.
Periodical inactive soil organisms only live in certain periods of their life-cycle in the soil, for example during overwintering or metamorphosis. Because of their relative inactivity they do not have a considerable role in soil ecology.
Periodical active soil organisms live a considerable period of their life-cycle in the soil. More development phase can be in the soil, like larva and cocoon.
Periodical soil living organisms live only a certain period of their life-cycle in the soil, like larva. However they repeatedly return to the soil during their lifetime, for example to oviposit, to prey or to find a shelter.
Permanent soil living organisms well adapted to the soil life. Because their high adaptation they cannot leave this environment. They are not protected against desiccation and temperature changes. Most of soil living microarthropod went trough some adaptations: reduction of visual organs, pigmentation lost, hiding coloration, reduction of different appendages, gaining different structures, which are essential for soil living. Permanent soil living animals are for example the earthworms.
Main groups and ecological functions of soil living invertebrates:
Nematodes are small, cylindrical, multicellular organisms. They are mainly aquatic species. In the soil they depend on the water-membrane surrounding soil particles. Considering species diversity, and individual abundance, among multicellular organisms, nematode is the most abundant group on Earth. Free living nematodes can be bacterivores, fungivorous, omnivores, plant parasites or predators. They are key species in the soil food web. Their role in mineralisation, decomposition is essential. However they can cause severe agricultural damages, only a few species can considered as pests. They are important for humans because of their role in nutrient-cycling or controlling pest insects.
Two main groups of molluscs attached to the soil, these are: snails and slugs. They can be found mainly on calcareous soil, because they depend on carbonates, which are essential component of their shell. Carbonate content of their shell can enrich the composition of the soil. Both group o can be found on the surface of soil and in the leaf litter. Phytophagous species can be considered as pests, but there are species which feed on decaying matter as well. Their slime can be an energy source for other organisms.
Ringed worms (Annelida)
They live on organic matter of the soil. These animals do not consume living parts of plants or roots (not pests). They consume the soil together with the plant remains (10-30 times of their own body weight per day). Their activity is followed by higher aeration, air capacity, water permeability of the soil. Their burrows can be used by plant roots to grow deeper so their ability to intake nutrients improves. For earthworms soil moisture is an important factor, they do not tolerate high temperature.
According to their distribution in the soil earthworms can be divided into three main ecological groups:
- Epigeic species: live on surface, in the leaf litter, humus layer, manure or compost.
- Anecic species: live in permanent burrows which is connected to the soil surface. Usually, during night they emerge to the surface to feed on dead plant material.
- Endogeic species: live in the soil, they almost never emerge to the surface. They feed on the organic matter of the soil.
Tardigrades are animals with barrel-shaped body and 4 pair of legs. They are closely related to arthropods. Their body is covered with strong cuticle. Their size is between 0,2-1,5 mm. Cosmopolitan species, they can be found all over the world in several habitat types, for example: brackish, aquatic, terrestrial habitats, from deep seas to high mountains. There are around 100 species in Hungary. Mostly they sucking up plant contents, but there are species which prey bacteria or which are parasites or other predators. They belong to the most resistant species on Earth. They can bare temperature change between -270 and 100 0C. They can live for 70 years.
Centipedes are arthropods which have one pair of leg per body segments. The first pair of legs was transformed to hook shaped, organs, which has poison ducts at its tip. They are very useful creatures in the garden because they control pest species. Centipedes are active at night and they prey on insects, worms and slugs. According to their body shape there are two main groups. Larger species live at the surface on rotting wood or in leaf litter. They have less segments but their legs are longer and stronger. They move relatively fast. The other groups bares shorter legs, their body is smaller, narrower and more elongated. They are specialized to live in the deeper soil.
They have two pairs of leg in each segment. They are also active at night, but contrary to centipedes they are not predators. They feed on algae, fungi and decaying matter. They live in the leaf litter or at the higher horizon of the soil.
Pale coloured, nine pair legged, centipede-like, blind arthropods. They have five pairs of sensory setae along their body. Their antennae are well developed, after the first segment these are divided in two branches. One branch is divided in two flagellae which bares sensor organs. With these organs the animal is able to sense its environment and physical effects. Pauropods live under stones, wet soil, under moss cover. They reach their highest density in the soil at 10-20 cm depth. They are sensitive to light. Their react with vertical migration to the moisture changes of the soil. They feed on dead plant material on fungi, but they can be predators as well.
Centipede-like, blind arthropods, but they are smaller and transparent. With their 12 pairs of legs, they are able for rapid movement between the soil particles. They can be found from the surface to 50 cm depth. Symphylas feed on decaying plant materials, but they can be considered as pests while they eat seeds, roots and root hairs. 200 species of Symphyla are known.
The segmentation of their body resemble scorpions, but they do not have elongated abdomen and does not bare venomous sting. Pseudoscorpions are smaller. Their pedipalps are large baring claws. With these claws they can grab their prey or defend themselves. It can contain venom sacs. Most of the species live under barks, burrows of other animals, but there are species which live even among pages of books. They are predators, their grab their pray with the claws. Mostly they feed on small insects and mites.
These are animals with short and stocky body, their abdomen is articulated. They have four pairs of long legs, which hold the body above the ground. They are active at night, during daytime they are hiding in dark and wet places. Contrary to spiders they are not all predators. Harvestmen feed on plant material, fungi, dead insects, decaying material as well.
This is a heterogeneous group. The head is separated from their cephalothorax. They are mostly round shaped animals. They have heterogeneous mouthpart depending on their lifestyle: biting, stinging, sawing or sucking. The adults have four pair of legs. They can occur in every type of soil. They live in several micro-habitat, where dead organic material is present: for example: peat, moss, lichen, tree bark. Several mite species are considered as pest in agriculture, apiculture or other fields. Herbivore mites suck the living part of plants. After destruction of plant tissue, they infect another healthy part. Their greatest threats are predatory mites.
The distribution of mites within the soil profile is unequal. Most of the species live close to the soil surface, which is rich in organic matter, bacteria and fungi. Depending on soil moisture, vegetation cover and distribution of organic matter, horizontally they usually appear in clusters. By fragmenting the organic matter and producing fine structured faeces, they contribute to the formation of structure and humus content of the soil. They can regulate the populations of other decomposers like fungi and bacteria. Most of soil living mite is blind.
Oribatid mites (Oribatidae)
Oribatids are relatively slaw, strongly chitinised, rotund mites. They are one of the most characteristic and diverse mite group in the soil. Presumably they are the most important group according to soil life. They have an important role in humus formation. They can be found on decaying plants, mosses, and decaying trunks. Mostly they feed on decaying material, fungi hyphae or even insect eggs.
Palpigrades live in soil and cave, they are blind. Tail-like posterior part is connected to their last segment, from which they gained their name. Their feed on eggs of other arthropods. They live in soil cracks, caves and under stones where humidity is uniformly high.
Their body is organized into two parts called the cephalothorax, and the abdomen, they have 8 legs. Spiders are predators. Species living on the ground hunt without net, they catch their prey by chasing relied on good vision. Almost every soil living animal can be considered as their prey. Spiders have an important role in pest control.
Isopods are dorso-ventrally flattened crustaceans, with 7 pair legs. The legs are of much the same size, morphology and orientation, giving the order its name “Isopoda” (equal legs). Their body is separated into cephalon (head), pereion and pleon (abdomen). The abdomen is hort. They have a strong anatomic conformation, they are covered with a thick cuticle. They can tolerate desiccation well even though they are crustacean, but there are species which are bonded to aquatic habitat. They occur most frequently under stones, under decaying wood and in leaf litter. They are active mainly at night. During their feeding they fragment dead plant remains and their faeces can be broken down easier by bacteria. However thy can feed on bacteria, fungi, plant and animal remains as well.
Proturans are primitive wingless hexapods, with cylindrical body. Instead of antennae they use their first pair of legs for sensoring, so they walk only on 4 legs. They have a slow movement and live approximately 1 year. They live in wet habitat, protected from light, in not too acidic soils with high organic content, on decaying plant material (decaying trunk, mosses, etc.) at the upper 3-10 cm of the soil. They are predators, but they feed on bacteria and fungi as well.
Many springtail species have a furcula at the end of their abdominal section. The furcular usually held folded beneath the animal, in a tension. In case of some danger it can put the animal into the air and escape it. Their distribution is wide, they can be found from the Artic to the Antartic everywhere in the soil. Springtails have a mixed feeding, they are mainly decomposers, they eat fungi, plant tissues, roots, leaf litter, algae, lichens, bacteria and nematodes or other springtails and their eggs. They have a high contribution to the humus formation. Horizontally and vertically, their distribution in the soil is very diverse. Certain species live on the surface of the soil, these are pigmented, these have long legs and antennae, their body is well haired. The eyes and legs of the soil-living species has reduced, they lost their pigmentation.
Symphypleona: They are very round animals, with long antennae. Their segmentation is blurred. They live on the surface and on plants.
Poduromorpha: They have a plump, but elongated body shape. Several species live in aquatic environment, some of them can bare extreme cold as well.
Entomobryomorpha: They are slender bodied animals, with quite long antennae. Their furca is very robust.
They are primitive hexapods, which have an elongated, colorless body with long antennae and two long cerca. They live in the ground, in mosses or in the leaf litter. They are predators or omnivorous species, which avoid the light. Form the 700 described species there is 10 living in Hungary. Diplurans never reach large abundance in the soil.
They belong to the group of the primary wingless insects. At the end of their abdomen, there are three filaments with equal length. Principally they feed on organic debris, but certain species can eat, cereals, pasta, glues, paper, dried meat as well. They are active at night. In the daytime they hide in cracks. Through their skin, they can absorb the humidity of the air so they can survive in dry environment as well.
Sok fajuknak ugróvillájuk van (furcula), amely a potroh végén elhelyezkedő képlet. Általában a potroh alatt található behajlítva, feszített állapotban. Veszély esetén ez a szerkezet tovaröpíti az állatot. Az Északitól a Déli-sarkig mindenhol előfordulnak a talajban. Táplálkozásuk vegyes főleg lebontók, gombafonalakat, növényi részeket, gyökereket, avart, algát, zuzmót, baktériumokat, fonálférgeket fogyasztanak. Más ugróvillásokat, vagy azok petéit fogyasztják. Nagymértékben hozzájárulnak a humuszképződéshez. Eloszlásuk a talajban mind függőlegesen mind pedig vízszintesen elég változatos. Bizonyos fajaik a talaj felszínén az avarban élnek. Ezek pigmentáltak, hosszú végtagjaik és csápjaik vannak, testük jól szőrözött. A talajban élő fajok, szeme és végtagjai redukálódtak, elveszítették pigmentáltságukat.
Ants (Formicidae): Ants have a slender body. Along wasps and bees they belong to the order of Hymenoptera. They are eusocial insects, they live in colonies which consist of several castes. They actively form the soil. Beside earthworms they have an important role in soil aeration and to improve air capacity and water permeability of the soil. They are able to make burrows in places where earthworms has a small abundance. With their storage, they bring back considerable amount of organic matter into the soil.
Earwigs are dorso-ventrally flattened insect. On their abdomen they bare a pair of forceps pincers. The one of the males is more robust and more curved than the ones of the females. First pair of wings are reduced, scale-like, under this, there are the second pair of wings folded. They are omnivorous, timid, hidden insects. They rarely use their pincers, only to fight among males, to frighten their enemies, or to open their wings. Primarily they feed on aphids, caterpillars and several types of eggs. They can damage the crops by chewing fruits or flowers. They are harmless for humans.
Cockroaches are nocturnal insects. At daytime they are hiding in cracks in the wall and other refugies. Mostly they are solitary but sometime they can appear in mass. Cockroaches have well developed olfactory senses, which they use for food searching. Mostly they feed on organic waste, they are omnivorous, but they prey on smaller arthropods as well.
There are several beetle families with several feeding habit. Among soil living beetles there are predators, herbivores and decomposers as well. The morphology of soil living beetles transformed during their evolution like it happened in case of springtails. Their size has reduced, their legs became shorter, body appendages has reduced, they lost their eyes. There are several groups which live in the soil only in the larval stage. The best known are scarab beetles (Scarabaeoidea), which feed on dungs of herbivorous animals and they burrow the dung into the soil. Other important groups is carrion beetles (Silphidae), which are able to burrow dead animals into the soil for their larvae. Both group have an important role in dead material recycling. There are beetles families which are herviorous and feed on roots and other parts of the plants under soil. They can be considered as pests. There are soil living predatory beetles too. For example Carabidae are nocturnal, moisture related insects. Most of them are predator, they feed on earthworms, snails, mites, springtails, caterpillars and eggs. But there are scavenger and herbivorous species as well. They move on the ground or on plants.
All of cicada species are herbivorous. Their larvae live in roots and suck their saps. The larva can live in the soil for a long time (even 17 years). Fully-grown larva goes on the surface and the adult insect hatches there.
Thrips are cylindrical or dorso-ventrally flattened animals, which hardly can be seen with the naked eye. They have fringed wings, but there are wingless species as well. They can live below- and aboveground as well. In the soil, they feed on living or dead animal or plant material. Plant sucking species can be considerable pests.
Main pest species:
1. Pests in apple culture:
Codling moth (Cydia pomonella) Link to pdf
Spotted tentiform leaf miner (Lithocolletis blancardella) Link to pdf
Pear leaf blister moth (Leucoptera scitella) Link to pdf
2. Pests in stone fruit cultures:
Cherry Bark Tortix (Enarmonia formosana) Link to pdf
Oriental fruit moth (Grapholita molesta) Link to pdf
Plum fruit moth (G. funebrana) Link to pdf
3. Pests in different orchards:
Lesser Bud Moth (Recurvaria nanella) Link to pdf
4. Pests in arable land and vegetable cultures:
Turnip moth (Agrotis segetum) Link to pdf
Cotton bollworm (Helicoverpa armigera) Link to pdf
5. Pests of stored crops:
Indian Meal Moth (Plodia interpunctella) Link to pdf
Mediterranean Flour Moth (Ephestia kuehniella) Link to pdf
6. Pests in arable land and vegetable cultures (YF):
Common click beetle (Agriotes sputator) Link to pdf
Common cutworm (A. ustulatus) Link to pdf
7. Pests in arable land and vegetable cultures (KLP):
Western corn rootworm (Diabrotica v. virgifera) Link to pdf