Diagram of head regions of a herbivore left and nematode bacterivore right. In the herbivore, the mouthpart is modified into a stylet for puncturing plant cells. In the bacterivore, the mouth or stoma is a hollow tube.
Many kinds of free-living nematodes feed only on bacteria, which are always extremely abundant in soil. In these nematodes, the "mouth", or stoma, is a hollow tube for ingestion of bacteria. This group includes many members of the order Rhabditida as well as several other orders which are encountered less often.
These nematodes are beneficial in the decomposition of organic matter. This group of nematodes feeds on fungi and uses a stylet to puncture fungal hyphae.
Many members of the order Aphelenchida are in this group. Like the bacterivores, fungivores are very important in decomposition. These nematodes feed on other soil nematodes and on other animals of comparable size. They feed indiscriminately on both plant parasitic and free-living nematodes. One order of nematodes, the Mononchida, is exclusively predacious, although a few predators are also found in the Dorylaimida and some other orders.
Compared to the other groups of nematodes, predators are not common, but some of them can be found in most soils. The food habits of most nematodes in soil are relatively specific. For example, bacterivores feed only on bacteria and never on plant roots, and the opposite is true for plant parasites.
A few kinds of nematodes may feed on more than one type of food material, and therefore are considered omnivores. For example, some nematodes may ingest fungal spores as well as bacteria. Some members of the order Dorylaimida may feed on fungi, algae, and other animals. Since free-living nematodes have not been studied very much, the food habits of some of them are unknown.
The microscopic size of these animals presents additional difficulties. For example, it can be very difficult to distinguish whether a nematode is feeding on dead cells from a plant root or on fungi growing on the cell surface. Beneficial nematodes help control disease and cycle nutrients. Credit: Elaine R. Please contact the Soil and Water Conservation Society at pubs swcs. Nutrient cycling. Like protozoa, nematodes are important in mineralizing, or releasing, nutrients in plant-available forms.
At low nematode densities, feeding by nematodes stimulates the growth rate of prey populations. That is, bacterial-feeders stimulate bacterial growth, plant-feeders stimulate plant growth, and so on. At higher densities, nematodes will reduce the population of their prey. This may decrease plant productivity, may negatively impact mycorrhizal fungi, and can reduce decomposition and immobilization rates by bacteria and fungi.
Predatory nematodes may regulate populations of bacterial-and fungal-feeding nematodes, thus preventing over-grazing by those groups.
Nematode grazing may control the balance between bacteria and fungi, and the species composition of the microbial community. Dispersal of microbes. Nematodes help distribute bacteria and fungi through the soil and along roots by carrying live and dormant microbes on their surfaces and in their digestive systems.
Food source. Nematodes are food for higher level predators, including predatory nematodes, soil microarthropods, and soil insects. They are also parasitized by bacteria and fungi. Disease suppression and development. Like bacterial feeding nematodes, fungal-feeding nematodes contribute to the process of nutrient mineralization by releasing N and other plant nutrients from consumed fungal tissue.
However, in agricultural systems, bacterial-feeding nematodes typically release more inorganic N than fungal-feeding nematodes. Predatory nematodes are of interest because of their role in regulating the populations of other organisms. They generally feed on smaller organisms like protozoa and other nematodes.
Thus they can help moderate population growth of bacterial- and fungal-feeding nematodes and protozoa, and help regulate populations of plant-parasitic nematodes. Insect-parasitic nematodes are species of bacterial-feeding nematodes that live in close association with specific species of bacteria; together, they can infect and kill a range of insect hosts.
The infective juvenile stage of insect-parasitic nematodes seeks out insect hosts to continue its development into adults. These bacteria multiply and overwhelm the immune response of the host insect, ultimately killing the host.
The nematodes feed on these bacteria, mature, and reproduce until all the resources within the insect host are consumed; then, infective juvenile nematodes escape the insect host's body and disperse in the soil to seek new hosts. Insect-parasitic nematodes are available commercially for use in inundative releases to manage the populations of a variety of insect pests.
Most plant-parasitic nematodes feed on the roots of plants. Some species attach to the outside surface of plant roots Fig. A relatively small number of important plant-parasitic nematode species are known to cause substantial economic damage in cropping systems around the world.
The determination of tolerance limits or economic thresholds for plant-parasitic nematodes varies with many factors like species, plant tolerance, and soil type.
Because plant parasitic nematodes show varying degrees of host specificity, carefully designed crop rotations are usually a powerful tool for reducing nematode-associated yield losses. Figure 3. White potato cyst nematode, Globodera pallida Stone Behrens, on plant roots. The earthworm species and species interactions present in the system also effect nitrogen mineralization and crop production [ 63 ].
This may result in enhanced nitrogen immobilization or mineralization depending on species characteristics and substrate quality. The review thus highlights the important effects that EWs have on C and N cycling processes in agroecosystems and that their influence depends greatly on differences in management practices [ 64 ]. Further the EWs can also increase nutrient availability in systems with reduced human influence and low nutrient status, that is, no tillage, reduced mineral fertilizer use, and low organic matter content [ 65 — 67 ].
The role of EWs in improving soil fertility is ancient knowledge which is now better explained by scientific results emerging from different studies. This is an important field of study where the research is directly linked to the social welfare [ 68 ]. Every involved step requires appropriate protocols and reproducible results. This is a feedback mechanism where the technology adopted in the fields is further improved in the laboratories based on the feedback received from the technology adopters so as to provide more convincing information to technology adopters.
Most of the studies conducted to assess the role of earthworm casting in nutrient cycling and soil structure are related to surface casting species, and only a few have dealt with casts deposited under field conditions [ 5 , 18 , 54 ]. To reach a better understanding of the ecological impact of in-soil casts, the assessment of nutrient dynamics in earthworm burrows and on the effect of in-soil casts on plant growth would be of immense help.
For below-ground casting earthworm species, the ecological impact of their below-ground casts is likely to be as important as their surface casts in relation with nutrient availability, especially for biological management of degraded and disturbed ecosystems.
Therefore more research is needed to be done in this area to complete our knowledge of the role of EWs in nutrient dynamics so as to evolve strategies for better soil management techniques. Considering the potential contribution of EWs to soil fertility management, there is the need to consider them in agroecosystem management decisions.
The EWs can specifically affect soil fertility that may be of great importance to increase sustainable land use in naturally degraded ecosystems as well as agroecosystems.
Proper earthworm management may sustain crop yields whilst fertilizer inputs could be reduced. Since farming can involve many soil disturbing activities, the understanding of the biology and ecology of EWs will help devise management strategies that may impact soil biota and crop performance.
This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors.
Read the winning articles. Journal overview. Special Issues. Academic Editor: Natchimuthu Karmegam. Received 26 Jul Accepted 22 Oct Published 14 Dec Abstract The soil biota benefits soil productivity and contributes to the sustainable function of all ecosystems. Introduction Protection of the soil habitat is the first step towards sustainable management of its biological properties that determine long-term quality and productivity.
Some properties of casts of Pheretima alaxandri and their underlying soils with and without litter cover [ 10 ]. Values followed by different subscript numbers are significantly different in same sampling sites [ 11 ]. Table 2. Effect of land conversion and management practices on changes in functional catagories of earthworms in the Indo-Gangetic plains, SE,.
Table 3. Variation in nutrient concentration of earthworm casts and noningested soils during cropping under shifting agriculture in North East India SE, [ 18 ]. Table 4. Variation in nutrient concentration of earthworm casts and non ingested soils in abandoned agricultural fallows in North East India SE, [ 18 ]. Table 5. C and N contents and C : N ratio in particle-size organic fractions in control soil and cast of Pontoscolex corethrurus SE [ 53 ]. Table 6. Total and mineral nitrogen content in soil and fresh casts from earthworms incubated in different soil types Barois et al.
Table 7. References D. Mora, C. Chotte, and C. View at: Google Scholar L. Brussaard, V. Behan-Pelletier, D. Bignell et al. View at: Google Scholar P. Lavelle and A. Lavelle, A. Chauvel, and C. Date, Ed. View at: Google Scholar C. Villenave, F. Charpentier, P. Lavelle et al. Lavelle, L.
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