Decomposition: Processes and Factors

In this article we will discuss about:- 1. Subject Matter of Decomposition 2. Processes of Decomposition 3. Factors.

Subject Matter of Decomposition:

Decomposers and transformers are the living components of the ecosystem and they are fungi and bacteria. Decomposers attack the dead remains of producers and consumers and degrade the complex organic substances into simpler compounds.

The simple organic matters are then attacked by another kind of bacteria, and transformers which change these organic compounds into the inorganic forms that are suitable for reuse by producers or green plants. The decomposers and transformers play very important role in maintaining the dynamic nature of ecosystems.

Decomposition concerns breakdown of complex organic matter by decomposers to inorganic raw materials like carbon dioxide, water and various nutrients. The upper layer of soil is the main site for decomposition processes in the ecosystem.

Dead plant parts and animal remains are called detritus.

Dried plant parts, such as leaves, stems, bark, flowers, etc., and dead remains of animals, including faecal matter, drop over the soil which constitute the aboveground detritus, which is also known as litter fall.

Contrary to it, the belowground detritus is composed of dead roots and also known as root detritus.

As the time passes, decomposing detritus loses weight, until it disappears completely.

Sometimes, when decomposition is retarded or stopped, large amount of partially decomposed organic matter is accumulated in the ecosystem.

Processes of Decomposition:

Generally, there are three main processes of decomposition.

They are:

(i) Fragmentation of detritus,

(ii) Leaching, and

(iii) Catabolism.

i. Fragmentation of Detritus:

This process takes place, mainly due to the action of detritus feeding invertebrates, also known as detrivores, where detritus is broken into smaller particles. Here, the detritus is pulverised, when passes through the digestive tracts (alimentary canals) of animals. Due to this process, the surface area of detritus particles is greatly increased.

ii. Leaching:

During this process, water percolating through soil removes soluble substances, such as sugars and several other nutrients, from the fragmented detritus due to leaching action.

iii. Catabolism:

During process of catabolism, the extracellular enzymes released by bacteria and fungi carry out enzymatic conversion of the decomposing detritus to simpler compounds and inorganic substances.

It is notable that all the above mentioned processes of decomposition operate simultaneously on the detritus,

Besides above mentioned decomposition processes, humification and mineralisation occur during decomposition in the soil.

Humification:

During this process of decomposition a dark coloured amorphous substance is formed and accumulated, which is called humus. This is highly resistant to microbial action and undergoes quite slow decomposition. Humus serves as a reservoir of nutrients.

Mineralisation:

A process, which results in the release of inorganic substances, such as CO₂, H₂O and other nutrients like NH₄⁺/Ca⁺⁺, Mg⁺⁺, K⁺, etc., in the soil.

Nutrient Immobilization:

During process of decomposition, under certain specific conditions, soil nutrients get tied up with the biomass of microbes and become temporarily unavailable to other organisms. This type of incorporation of nutrients in living microbes is called nutrient immobilisation.

Such nutrients remain immobilised for variable periods and get mineralised later, after the death of microbes.

The immobilisation of nutrients prevent them from being washed out from the ecosystem.

Factors Affecting Decomposition:

The rate of decomposition of detritus is primarily regulated by factors categorised under two important heads:

(i) Climatic conditions, and

(ii) Chemical quality of detritus.

i. Climatic Conditions:

Here, key role is played by temperature and soil moisture, which have their effect on the activities of soil microbes.

Detritus decomposes very rapidly, within a few weeks or months, in a climate where higher temperature prevails, i.e., more than 25°C, and moist conditions remain constant for long time, e.g., in humid tropical regions.

However, low temperature, i.e., less than 10°C, sharply reduces decomposition rate even if moisture is in abundance. For example, in regions of high altitude, complete decomposition of detritus takes place in several years or decades.

Decomposition rate is lowered in prolonged dryness of soil, even if the temperature remains high, as found in tropical deserts.

ii. Chemical Quality of Detritus:

The accumulation of certain substances is responsible for promotion or retardation of rate of decomposition. The chemical quality of detritus is determined by the relative proportions of water soluble substances, which include sugars, polyphenols, lignin and nitrogen.

Even, within same climatic conditions decomposition rate becomes slower, if the detritus is rich in lignin and chitin. The nitrogen-rich detritus, on the other hand, having low amounts of lignin, decomposes relatively rapidly.

However, the overall rate of decomposition of detritus in natural conditions depends upon the combined effect of environmental conditions and quality of detritus.