n., plural: decomposers
Definition: organisms that carry out decomposition as it feeds on decaying organisms and recycles nutrients
The organisms that carry out the process of decay or breakdown of the dead organism are known as decomposers and the process of breaking down complex organic matter into its simpler form is referred to as decomposition. In environmental science or ecology, decomposers are the organisms that are involved in the process of decomposition of the dead, both animal as well as plant matter, in the ecosystem.
So, what do these decomposers do, and why are decomposers important? These organisms are the critical component of the food chain in the ecosystem responsible for the breaking down of the organic and nutrient matter of the dead, thus recycling the organic matter and making it available to the ecosystem. This organic and nutrient matter is absorbed or taken up by the plants or the producers of the ecosystem, and, thus, these essential components re-enter the food cycle. This is how decomposers interact with the ecosystem. Decomposers occupy the lowest most position in the ecological pyramid, however, they form the critical base for the life on the ladder above them. The decomposers are heterotrophic as they derive the energy for their survival from the dead matter.
Decomposers are the most important component for the soil ecology as they feed upon the dead mass, which in the process gets broken down into essential molecular elements like carbon, calcium, nitrogen, etc., and becomes available in the soil for plants. Saprophytes carry out the digestion process externally, i.e., outside their body. Saprophytes secrete digestive enzymes to break down the organic dead mass and convert them into simpler substances. For example, proteins are broken down by saprophytes into amino acids, carbohydrates into simple sugars, and fats/lipids into fatty acids and glycerol. Fungi and bacteria are the common saprophytes that survive on saprophytic nutrition. The optimum condition for the survival and growth of saprophytes includes the presence of oxygen, high humidity/moisture, neutral or acidic pH, and temperature in the range of 1 to 35 °C (25 °C being optimum). Yeast, mucor, and Penicillium are examples of saprophytic organisms. These saprophytes have certain common features:
- Have filaments
- Lack of leaves, roots, and stems.
- Heterotrophic in nature as it cannot carry out photosynthesis
- Produce spores
Importance or the Function of Decomposers
The primary function of the decomposers is to carry out the disintegration or decomposition process of the dead organisms.
Ecological cleansers and balance providers
Decomposers are ecological cleansers that disintegrate the dead, plants as well as animals. By decomposing the dead, decomposers also help to create a biosphere for new life. Thus, decomposers play a crucial role in creating a balance in the ecosystem.
Recycling of nutrients
Decomposers disintegrate the dead matter into basic components like carbon, oxygen, nitrogen, phosphorus, etc., thus, making these primary essential elements available in the environment to be taken up by the plants, thus, recycling the nutrients. they can be absorbed by the producers (e.g. plants and algae) of the food cycle. Decomposers provide the essential nutrients that are required for the survival of ‘producers’ in the food chain. Though decomposer occupies the lowermost position in the food web, they are the most critical component of the food web. To understand how decomposers interact in their ecosystem in terms of the food chain and food web, refer to Figure 1 and the video below.
Decomposers and Scavengers
Decomposers, as well as scavengers, are an important part of the food cycle involved in the ecological recycling of nutrients and organic matter. However, the two classes of organisms differ in their mechanism of work. Essentially, scavengers are the initiators of the process of decomposition which is eventually taken over by the decomposers. The key difference between the class of organisms is listed in the table.
Table 1: Difference between Decomposers and Scavengers
|Initiate the process of decomposition by breaking down the dead mass into small particles||Act on the small particles that are made available due to the action of scavengers and break down further to yield the basic elements like carbon, calcium, phosphorous, etc.|
|Initiators of the decomposition process||Finisher of the decomposition process|
|Insects (e.g. cockroaches, flies, etc), birds (e.g., vultures) fishes, and crabs||Bacteria, Fungi, and Invertebrates (e.g. earthworms and millipedes)|
Types of decomposers
Basically, there are four types of decomposers, namely fungi, insects, earthworms, and bacteria.
Fungi are heterotrophs. They do not carry out photosynthesis and are the principal decomposers in the ecosystem. Algae, which are another group of organisms, are not decomposers; in fact, algae are producers as they possess photosynthetic pigments that enable them to carry out photosynthesis. So while algae are the producers of a food chain, the fungi take the role of the decomposers. And since mushrooms are a type of fungi they are regarded as decomposers as well. This, thereby, answers these common questions — “are fungi decomposers?” or “are algae decomposers?” or “are mushrooms decomposers?”
Fungi are the decomposers that disintegrate the litter by pre-digesting, i.e., releasing enzymes in the environment to break down the litter. The enzymatic secretion by the fungi breaks down the dead matter in the process of digesting it, which is eventually taken up or absorbed by the fungi themselves. Since fungi decompose the dead matter and draw nutrients from it, they are also classified as saprotrophs. High humidity is a must for the growth and survival of the fungi and also for the process of decomposition.
Flies, dung beetles, maggots, and ants are the insects that help in carrying out the process of decomposition in the ecology. Insects fall under the category of detritivores as they carry out internal digestion of the litter in their intestinal tract. There are various classes of insects that are engaged in the process of decomposition, which is classified based on the type of dead matter they feed upon:
- Dead or decaying plant tissues feeding insects
- Dead animals or tissue-feeding insects
- Excrement-feeding insects (eg: Arthropods like the dung beetle)
Detritivores are organisms that orally feed on the dead matter (both plant as well as animal origin) and fecal waste and break down the litter in their intestinal tracts. So, are worms decomposers?”
Earthworms are a classical example of worms that enrich the soil by decomposing the litter. The earthworms feed upon the dead matter as well as fecal waste and in their intestinal tract, the litter is treated by the enzymes resulting in the breakdown of the litter, which is eventually expelled by the earthworm into the soil. These worms enrich the soil with essential elements like phosphate and calcium etc. Worms play a critical role in the ecology of the soil.
These ubiquitous, microscopic organisms are the crown holder of the process of decomposition. So, this answers the most common question ‘are bacteria decomposers?’ Bacteria help to recycle essential nutrients like nitrogen and carbon etc and make them available to the producers in the food chain. Bacteria are also classified as saprotrophs.
Decomposers: Detritivores and Saprotrophs
Decomposers are a group of organisms that essentially break down decaying organic matter. There are two major groups that make up the decomposers: detritivores that feed on dead matter and saprotrophs. Detritivores (sometimes simply called detrivores) include animal decomposers whereas saprotrophs (also called saprobes) are exemplified by fungi and bacteria. Although decomposers and detritivores are sometimes used synonymously they are two distinct terms. Although the term “decomposer” is a more inclusive term to include not just the saprotrophs but also detritivores.
Table 2: Difference between Decomposers, Detritivores, and Saprotrophs
|Decomposers are a more inclusive group of organisms that decay the dead matter They include detritivores and saprotrophs.||Detritivores are organisms that feed orally on dead matter, to gain nutrients and energy.||Saprotrophs are organisms that break down dead matter|
|Examples of decomposers: fungi, bacteria, earthworms, insects||Examples of detritivores: millipedes, earthworms, crabs, flies, etc.||Examples of saprotrophs: fungi and bacteria|
|Decomposers act on the dead matter, e.g. by secreting the enzymes and digesting the matter externally.||Detritivores contribute to the decomposition process, particularly, by ingesting the dead matter, and then digesting it in their digestive tract||Saprotrophs contribute to the decomposition process by extracellular digestion, i.e., they digest dead matter externally by secreting enzymes and then absorbing the nutrients.|
|Decomposers metabolize large clumps of dead matter but at different paces||Detritivores can feed upon large clumps of dead matter and metabolize them faster than saprotrophs||Saprotrophs do not feed on them but can still decompose them although relatively slowly|
Let’s find out what decomposition is, how the decomposers carry it out, and the factors affecting the process.
Definition of decomposition
What is decomposition? It is the process of breaking down complex organic matter into a simple form. Any organic matter, dead or waste or excreta is acted upon by the decomposers i.e., bacteria, fungi and is broken down into simple organic molecular forms.
Stages of decomposition
Every living being on earth eventually dies off. Once dead, the process of decomposition must initiate for the continuation of life on earth. Decomposition is the essential step of recycling essential matter into the food cycle. The process of decomposition is essentially comprised of five stages.
As the name of this stage suggests, the dead mass is fragmented. That means the large pieces are turned into smaller pieces. Fragmentation of the large mass increases the surface area of the detritus. This step is the initiation of the decomposition process carried out by detritivores. The detritivores engulf the dead mass and in their gastrointestinal tract, the large mass of the dead matter is broken into small pieces for the decomposers to act upon.
Fragmented detritus contains a lot of water-soluble nutrients organic (simple compounds) as well as inorganic in nature. The water that percolates through the soil, dissolves these water-soluble nutrients and enriches the soil with them by the process of leaching.
Once the detritus is fragmented and water-soluble nutrients are removed from the detritus, enzymes released by the decomposing fungi and the bacteria act upon the detritus. These enzymes catabolize the detritus further to break down the complex matter into simple molecular nutrients.
The process of catabolism is followed by the process of humification. Humification is the process of the formation of humus. Humus is the highly nutrient-rich, dark-colored layer on the soil which is made up of amorphous substances. This layer is extremely resilient to any action of the microbes. This layer of soil contributes majorly to the fertility of the soil.
In the last step of decomposition, the inorganic substances such as Ca+2, Mg+2, K+1, NH4+1, etc. along with CO2 and H2O are released into the soil, thus further enriching the soil with the nutrient matter.
Under certain specific conditions during decomposition, certain soil nutrients get bound with the microbial biomass and this results in the unavailability of the nutrients to other organisms. This type of integration of nutrients with living microbes is known as nutrient immobilization. Though, the period of immobilization and availability of such nutrients is variable and may even get mineralized only after microbial death. This immobilization of nutrients thwarts the washing off of such nutrients from the ecosystem.
Here, it is important to understand the difference between the process of decomposition and putrefaction, which may be confused as synonyms. Decomposition is the process of break-down of organic dead matter into simpler forms of matter. Putrefaction is a stage of decomposition wherein protein breakdown of the dead mass occurs. As a result of the protein breakdown, the cohesiveness of the tissue is lost and the breakdown of the tissue occurs.
Factors affecting decomposition
A number of factors affect the rate of the process of decomposition-
- Quality of Litter. The structural and chemical properties of the litter strongly affect the rate of decomposition. For eg., the presence of lignin in the litter of bryophytes results in slower decomposition of the bryophytes.
- Temperature. It is a well-established fact that the growth and activity of microorganisms are governed by temperature. Thus, the temperature change in different geological conditions also affects the process of decomposition. Lowering the temperature, as seen on higher altitudes with low temperatures, significantly slows down the process of decomposition. This can be attributed to the slow microbial growth at low temperatures.
- Aeration. The majority of the decomposers especially decomposing bacteria are aerobic in nature. Thus, oxygen becomes an essential element for the process of decomposition. In soil, oxygen is present in the pores of the soil.
- Soil pH. The pH that would enable the decomposers to grow optimally will hasten the process of decomposition. Generally, decomposers thrive in a neutral or slightly acidic pH. Alkaline pH is not supportive of the process of decomposition. Interestingly, this principle is utilized for fixing the tissue/organ specimen on the slide for microscopy with the help of formaldehyde.
- Inorganic Chemicals. The chemical quality of detritus affects the rate of decomposition. The presence of inorganic minerals can slow down the process of decomposition.
- Moisture. For the physiological processes of microbes, the presence of water or humidity is essential. The amount of moisture thus governs the growth of the microbes, which in turn affects the process of decomposition.
Thus, it can be concluded that the quality of detritus and the environmental conditions affect the process of decomposition.
Each ecosystem has different kinds of decomposers. Depending on the terrain or the ecosystem, the kinds of decomposers are enlisted below.
Decomposers in the aquatic ecosystem
(1) Oceans/ Seawater decomposers: tropical temperatures like that of the Pacific Ocean favors the growth and survival of the decomposers in the sea/oceans. Some of the commonly found decomposers of the oceans/seawater are:
- Christmas tree worms, capture the floating organic matter with the help of their feathery appendages
- Crabs are considered the sea scavengers
- Granulated sea star, cleans up the dead matter in the sea by moving along the rocky surface.
- Hagfish are scavengers that feed upon seawater carcasses and take up the nutrients from them.
- Sea urchins, are the consumers as well as decomposers that feed on the Scarpe rock matter
- Tube worm
(2) Freshwater decomposers: Herein, the decomposers are mostly found in the bed of river, ponds, or lakes. Some of the commonly found decomposers of freshwater are:
- Mildew, a kind of marine bacteria
- Trumpet snail, a freshwater snail that is a scavenger and is considered a pest
- Water mold, fresh water, or a soil bacterium
- Yeast, freshwater bacteria
Terrestrial Ecosystem Decomposers
(1) Forest Ecosystem Decomposers: forest bed has different decomposers. Some of them are:
- Beetle, are the shredders that feed upon detritus
- Earthworms feed upon detritus
- Millipede, another shredder that feeds upon detritus
- Mushroom is a kind of fungi that breed on the ground or the dead material
- Pillbug, another shredder that feeds upon detritus
- Saprobe, a kind of soil bacteria
- Slime mold, a kind of saprobe growing on the rotten damp wood and leaves
- Slug, another shredder that feeds upon detritus
(2) Desert Ecosystem Decomposers: deserts are the low humidity ecosystem so conventional decomposers (Fungi or bacteria) do not exist in the desert ecosystem. Only insect decomposers exist in the desert ecosystem. Some of them are as follows:
- The dung beetle, animal feces-feeding bacteria
- Fly, decaying matter feeding insect
- Millipede, decaying plant material feeding insects
- Saharan silver ants are deserts ants that feed on animal carcasses
(3) Grassland Ecosystem Decomposers: this can be similar to forest ecosystem desert. Some of the common examples are:
- Acido bacteria, a specific bacterium that is found in grasslands or savannas
- Termite, insects that break down the cellulose of the wood
- Turkey tail and mushroom are the fungus feeding on dead logs
(4) Mountain Ecosystem Decomposers: these are also similar to forest ecosystem decomposers. Some of the examples are:
- Bolete mushrooms are the fungi feeding on the ponderosa pine tree by-products.
- Mountain pine bark beetle, dying and dead trees feeding insects
- Purple fairy fingers, fungus feeding on the decaying trees
Try to answer the quiz below to check what you have learned so far about decomposers.
- Buresova, A., Kopecky, J., Hrdinkova, V., Kamenik, Z., Omelka, M., & Sagova-Mareckova, M. (2019). Succession of Microbial Decomposers Is Determined by Litter Type, but Site Conditions Drive Decomposition Rates. Applied and environmental microbiology, 85(24), e01760-19. https://doi.org/10.1128/AEM.01760-19
- Floudas, D., Bentzer, J., Ahrén, D., Johansson, T., Persson, P., & Tunlid, A. (2020). Uncovering the hidden diversity of litter-decomposition mechanisms in mushroom-forming fungi. The ISME journal, 14(8), 2046–2059. https://doi.org/10.1038/s41396-020-0667-6
- Krah, F. S., Bässler, C., Heibl, C., Soghigian, J., Schaefer, H., & Hibbett, D. S. (2018). Evolutionary dynamics of host specialization in wood-decay fungi. BMC evolutionary biology, 18(1), 119. https://doi.org/10.1186/s12862-018-1229-7
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