Decomposers- Definition, Types, Examples, Decomposition

Decomposers are the organisms that decompose or break down the complex organic compound into simpler forms in a dead body, and the process of breakdown of complex compounds into simpler compounds refers to decomposition.

Decomposers are reducers or saprophytic, which means they live in the dead body and acquire nourishment from feeding decaying organic matter.

They include microorganisms (like fungi, bacteria), insects, earthworms, etc. They produced different digestive enzymes to break down the organic materials.

Decomposers are responsible for the flow of energy and recycling of the material in the ecosystem.

Decomposers provide essential nutrients to the soil needs of the producers by feeding the dead organic matter left by consumers and recycling it.

Type of decomposers

Four types of decomposers are involved in decomposition which are fungi, bacteria, insects, and earthworms.

Fungi

• Fungi are spore-forming, heterotrophs organisms that decompose or break down dead or decaying organic materials.
• Fungi are the principal decomposer in the ecosystem due to they do not involve in photosynthesis, but algae are not decomposers.
• The decomposer fungi release enzyme in the environment for the breakdown of liters (i.e., pre-digesting process). That enzyme breaks down the dead material during the process of digestion which is ultimately taken up or absorbed by the fungi itself.
• Fungi, including Trichoderma reesei, Aspergillus phoenicis, and Penicillium echinulatum are decomposer fungi. These fungi produce enzyme-like glucosidase, cellobiohydrolase, and cellobiose dehydrogenase that break down cellulose, hemicellulose, pectin, xylene, etc.

Bacteria

• An abundant amount of bacteria are present in the soil environment, in both the dormant and vegetative forms. They are involved in the early stages of decomposition.
• Bacteria can break down different organic compounds by releasing different types of enzymes. For example, Streptomyces and Acidothermus produce the enzyme endonuclease (endo-1-4-B glucanase), which breaks down cellulose by breaking the internal bond.
• Bacterial decomposer includes Proteobacteria, Actinobacteria, Bacteroidetes, Alphaproteobacteria, Gammaproteobacteria, etc.

Insects 

• Insects are considered to be detritivores (secondary decomposers) that feed dead material by mouth and digestion of the litter in their intestine.
• The significance of these organisms is that they are capable of feeding on a wide variety of organic matter, including animal parts, plants, and also other insects. 
• Flies, dung beetles, maggots, and ants are insects decomposer.
• Properly developed digestive systems are absent in maggots. Due to this reason, they produce different enzymes (e.g., serine, protease, leucine, aminopeptidase, carboxypeptidase). These enzymes are involved in the breaking down of various organic materials and require nutrients obtained for the growth and development of decomposers.

Earthworms

• The earthworm is the most common example of an animal decomposer. They feed on dead animals and plants as well as fecal waste, and in their intestine, litter reacts with enzymes resulting breakdown of litter. The end product is expelled into the soil, and its mix with soil helps in soil fertility.
• Many farms and farmers use worms for the decomposition of various organic matter to produce compost, which improves soil fertility. 

Importance of Decomposers

1. Decomposers break down dead animal matter and dead plants. From the decomposition, nutrients and energy are recycled and back into the ecosystem to be used again.
2. The main decomposer found in many ecosystems are fungi, especially in the forest; they help release phosphorus and nitrogen from dead material.
3. Decomposers clean up the dead material by decomposition process, and returning the nutrient to the soil nutrient is required for the producer.
4. Decomposers maintain the whole biogeochemical cycle of an ecosystem. If the decomposition is damaged or dies, the whole ecosystem is affected.
5. Decomposers decompose dead material and create space for new being or new life in the biosphere.
6. They help to recycle or put back the nutrient and other important elements like calcium, nitrogen, and phosphorus into the water, soil, and air for reuse by a producer like a crop plant.
7. Decomposers regulate the food chain. They break a dead organic compound into the simpler inorganic compound so the producer can use them to grow.
8. They are responsible for nitrogen fixation in the soil. They change nitrogen into a simpler form such as ammonia, nitrate, and nitrite that can be used by other organisms or plants in the food chain.

Detritivores and Scavenger

Detritivores

• Decomposers are two major groups, including detritivores and saprotrophs. Detritivores are heterotrophic organisms that feed orally on the dead matter to obtain nutrients and energy.
• Detritivores eat dead matter and then digest or break down it in their intestinal tract, so it contributes to decomposition.
• Detritivores is branch of decomposer. It plays an essential role in most biogeochemical cycles like the nitrogen cycle, carbon cycle, and phosphorous cycle.
• Examples of detritivores are insects (such as mites, butterflies, mites), flies, crabs, millipedes, woodlice, earthworms, etc.

Scavenger

• Scavengers and decomposers are an important part of the food chain involved in an ecosystem for recycling nutrients and organic matter.
• Scavengers are known as the initiator of the decomposition process. They initiate the decomposition process by converting dead mass into small particles.
•  Examples of scavengers are insects (flies, cockroaches), fishes, crabs, and birds (vultures).

What is Decomposition?

Decomposition is the process of breaking down complex organic substances into simpler substances by the action of a decomposer (microorganisms, insects, and worms).

It is the metabolic process, taking raw material and convert into a complex compound, processing it, and then breakdown into a simpler compound.

Decomposition of dead materials is an essential part of all life cycles on earth. This process serves essential nutrients and minerals for plants and also for the development and proper growth of new organisms.

Steps of decomposition

During the decomposition process of organic matter, the following five steps occur simultaneously.

1. Fragmentation

• This process is initiated by detritivores. It is the first stage of decomposition. Fragmentation means the breakdown of the large piece (detritus) into smaller pieces.

2. Leaching 

• Fragmented particles may contain water-soluble nutrients. The nature of these nutrients is inorganic. These nutrients get dissolved in water and seep into the soil.

3. Catabolism 

• When the complex or large compound changes into smaller particles and the inorganic nutrient are removed, the enzyme is released by the decomposer. These enzymes convert or break down detritus into the simpler inorganic compound.

4. Humification

• It is the process of formation of humus. Humus is a dark-colored, highly nutrient-rich layer on the soil. This layer is made up of amorphous substances which are highly resistant to any action of the microorganism. Humus provides high fertility to the soil.

5. Mineralization

• The conversion of organic matter into inorganic compounds or minerals is called mineralization. Some of the minerals like NO₃^–, PO₄^3-, etc., are important plant nutrients. Besides these, CO₂, H₂O, Ca⁺, NH₄⁺, SO₄^2- etc., are generated and released into soil during mineralization.

Factor affecting decomposition

1. Quality of litter: The rate of decomposition depends upon the structural and chemical characteristics of litter. If lignin is present in the litter, then the decomposition rate is slower.
2. Temperature: The rate of decomposition is high in mesophilic ranges. At higher temperatures, very little decomposition occurs because only a few decomposers can grow in the thermophilic range.
3. Moister: Sufficient moisture required for microbial activity and decomposition of organic matter. 
4. Aeration: Most decomposers are aerobic, so oxygen becomes an essential element in the decomposition process. In soil, oxygen is found in the pores of the soil.
5. Soil p^H: Soil organisms can grow in acidic (fungi), neutral (bacteria), and slightly alkaline (actinomycetes) p^H.  rate of decomposition is high in neutral to slightly alkaline soil.
6. Inorganic chemicals: Rate of decomposition affected by the chemical quality of detritus. A higher number of inorganic minerals present in dead material can slow down the rate of decomposition.

Example of decomposers

1. Decomposers in ocean aquatic system: Christmas tree worm, Crabs, Hagfish, Granulated sea star, Sea urchin, and Tube worm.
2. Decomposers in freshwater: Mildew, Trumpet snail, Water mold, Yeast, and freshwater bacteria.
3. Forest ecosystem decomposer: Beetle, Earthworm, Millipede, Mushroom, Pillbug, soil bacteria, and slime mold.
4. Grassland ecosystem decomposer: Acido bacteria, Termites, Mushrooms.
5. Mountain ecosystem decomposer: Bolete mushroom, Fungus, Mountain pine bark beetle, etc.

References

1. Mooshammer, M., Wanek, W., Zechmeister-Boltenstern, S., & Richter, A. A. (2014). Stoichiometric imbalances between terrestrial decomposer communities and their resources: mechanisms and implications of microbial adaptations to their resources. Frontiers in microbiology, 22.
2. 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.
3. Deacon, L. J., Pryce-Miller, E. J., Frankland, J. C., Bainbridge, B. W., Moore, P. D., & Robinson, C. H. (2006). Diversity and function of decomposer fungi from a grassland soil. Soil Biology and Biochemistry, 38(1), 7-20.
4. https://www.biologyonline.com/dictionary/decomposer.
5. https://byjus.com/biology/what-is-decomposition.
6. https://education.nationalgeographic.org/resource/decomposers.
7. https://biologydictionary.net/decomposer.