Concept of Ecosystem - Decomposition

The dead remains of plants, animals and faecal matter that serve as raw material for decomposition is called detritus.

Decomposition is the process by which decomposers break down complex organic matter into simple inorganic substances like carbon dioxide, water, and nutrients.

The enzymatic degradation of detritus into simpler inorganic substances by bacteria and fungi is called catabolism.

The formation and accumulation of a dark-coloured, amorphous, resistant substance during decomposition is called humification.

The conversion of humus into inorganic nutrients by microbial action is called mineralisation.

The dark-coloured, colloidal, nutrient-rich substance formed during decomposition that decomposes very slowly is called humus.

Decomposition is the process by which decomposers break down complex organic matter into simple inorganic substances like carbon dioxide, water, and inorganic nutrients. It is the process that involves the breakdown of complex organic matter from the body of dead plants and animals with the help of decomposers into simpler inorganic substances.

Raw Material: Detritus

• The raw material of decomposition is called detritus
• Detritus consists of the dead remains of plants and animals
• It includes fallen leaves, bark, flowers, dead animal matter, and faecal matter

1. Fragmentation

• It is the breakdown of detritus into smaller particles
• Carried out by organisms called detritivores (e.g., earthworms)
• By breaking detritus into smaller pieces, detritivores increase the total surface area of detritus available for further decomposition

2. Leaching

• Water-soluble inorganic nutrients present in detritus move downward through the soil
• These nutrients pass into the soil horizon and precipitate as unavailable salts
• These salts are temporarily locked away and not immediately available to plants

3. Catabolism

• Bacterial and fungal enzymes act on detritus and degrade it chemically
• This enzyme-mediated process converts detritus into simpler inorganic substances
• It is distinct from fragmentation - catabolism is a chemical process, whereas fragmentation is physical

4. Humification

• Leads to the accumulation of a substance called humus
• Humus is a dark-coloured, amorphous (structureless) substance
• It is colloidal in nature and therefore acts as a reservoir of nutrients in the soil
• Humus is highly resistant to microbial action and therefore decomposes very slowly
• It forms a stable organic layer in the soil

5. Mineralisation

• Humus is further degraded by certain microbes
• This degradation releases inorganic nutrients back into the soil
• Mineralisation is the final step through which nutrients become available again to producers (plants)

Decomposition is controlled by two major categories of factors:

A. Chemical Composition of Detritus

Decomposition is faster when detritus is rich in:

• Nitrogen
• Water-soluble substances (e.g., simple sugars, proteins)

Decomposition is slower when detritus is rich in:

• Lignin - a tough, structural plant compound
• Chitin - found in fungal cell walls and insect exoskeletons

B. Climatic / Environmental Factors

Nature of the Process:

• Decomposition is largely an aerobic (oxygen-requiring) process
• In the absence of oxygen, the process is inhibited, and organic matter breaks down incompletely

End Products of Decomposition:

The inorganic substances released at the end of decomposition are:

• Carbon dioxide (CO₂)
• Water (H₂O)
• Inorganic nutrients (mineral ions such as nitrogen, phosphorus, potassium, etc.)

These are returned to the soil and atmosphere, where they become available to producers (plants) once again, thus completing the nutrient cycle.