Question

What is decomposition? Write down its steps. Give a diagrammatic representation of decomposition cycle in a terrestrial ecosystem.

Answer 1

Decomposition is a process in which organic complex substances are broken down into simple inorganic substances like CO${}_2$, water and nutrients by decomposers like an earthworm. The major site of decomposition is the upper layer of soil in terrestrial habitat and bottom of water bodies. Dead remains such as leaves, bark, flowers and dead remains of animals including faecal matter constitute detritus which is the raw material for decomposition.

It involves the following steps:

1. Fragmentation: The process of breaking down of detritus into smaller particles is called fragmentation. It is done by earthworm and termites. Due to fragmentation, detritus is changed into fine particles which have a large surface area.
2. Leaching: The process by which water-soluble inorganic nutrients (e.g., sugars, inorganic nutrients) go down into the soil horizon and get precipitated as unavailable salts is called leaching.
3. Catabolism: The enzymatic process by which degraded detritus is converted into simpler inorganic substances is called catabolism. It is carried out by saprotrophic bacteria and fungi.
4. Humification: The process of accumulation of a dark-coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at the extremely slow rate is called humification. Humus is slightly acidic, colloidal and functions as a reservoir of nutrients.
5. Mineralisation: The process by which humus is further degraded by some microbes to release inorganic nutrients is called mineralisation. They are formed along with simple and soluble organic substances when digestive enzymes are poured over the organic matter by saprotrophic microbes.