Page 2 - Lesson note-Ecosytem

the rate of production of organic matter during photosynthesis and NPP is the remaining
biomass after respiration (R).

GPP –R = NPP

NPP is the available biomass for consumption to heterotrophs. Secondary productivity is
defined as the rate of formation of new organic matter by consumers.

Decomposition- breakdown of complex organic matter into inorganic substances like carbon

dioxide, water and nutrients is called decomposition. Dead plants remains like leaves, bark,

flowers and dead remains of animals constitute detritus. Decomposition involves following
steps- fragmentation, leaching, catabolism, humification and mineralization.

1. Fragmentation of Detritus: Detritivores feed on detritus ---breakdown --- increases the
surface area of detritus particles for microbial action.

2. Leaching: Soluble inorganic nutrients dissolve in water -– percolate through the soil ---
removed due to leaching action.

3. Catabolism: Decomposers (bacteria, fungi) release enzymes --- decompose detritus ---

simpler inorganic compounds.
4. Humification: Simplified detritus--- converted to humus

- Humus is a Dark, Amorphous substance.

- Highly resistant to Microbial Action

- Undergoes Decomposition very Slowly.

- Reservoir of nutrients (due to colloidal nature)

5. Mineralisation: Humus is degraded – releases inorganic substances

+
2+
2+
( CO , H O etc) and nutrients (Ca , Mg ,K etc)
2
2
Factors affecting rate of Decomposition:

1. Chemical composition - decomposition rate will be slow when detritus is rich in lignin and
chitin and rate increases when detritus is rich in nitrogen and water soluble substances like

sugars.

2. Climatic conditions – warm and moist environment favour decomposition and low

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