Productivity

productivity - primary & secondary productivity

1. productivity DILSHANA FATHIMA M.Sc. BIOCHEMISTRY

2. INTRODUCTION The term productivity is used to denote the amount of accumulated organic matter in a given time. The term productivity represents the rate of production in a system. The productivity can be classified into 2 Primary productivity Secondary productivity

3. P rimary Productivity It is the rate at which radiant energy is converted by photosynthetic & chemosynthetic activity of producers to organic substances. i.e , the rate of accumulation of dry matter by the plants through photosynthesis & chemosynthesis. It is expressed in terms of gm/m²/day. It is further classified into 3 Gross primary productivity Net primary productivity Net community productivity

4. Gross primary productivity (GPP) The rate of total capture of energy/the rate of total production of organic material. Is the total rate of photosynthesis including the organic matter used up in respiration during the measurement period. It is the total amount of food energy formed in a given time during photosynthesis. Net primary productivity (NPP) It is the rate of storage of organic matter in plant tissues exceeding the respiratory use by plants during the period of measurement.

5. The balance energy/biomass remaining after meeting the cost of respiration of producers is called NPP. NPP = GPP – Respiration rate NPP results in the accumulation of plant biomass, which serves as the food of herbivores & decomposers. Net community productivity (NCP) It is the rate of storage of organic matter not used by heterotrophs during the period under consideration. NCP = NPP – Heterotrophic consumption

6. Secondary productivity The rate at which food energy is assimilated at the trophic level of consumer. The primary producers have produced the food of consumers & secondary productivity reflects only the utilization of this food for production of consumer biomass. The primary consumer takes in chemical potential energy in the form of food from plants. Most of it dissipates in the form of heat & is lost out of the ecosystem. Only a small part of energy is fixed in the form of chemical potential energy in the protoplasm.

7. The same process is repeated at the secondary consumers or the primary carnivorous levels & so on. Hence, at each step of energy transfer from 1 trophic level to another, a large amount of energy is degraded into heat & never returns to the ecosystem.

8. DIFFERENCE PRIMARY PRODUCTIVITY SECONDARY PRODUCTIVITY Rate of synthesis of organic matter by producer. Comparatively quite high. Due to synthesis of fresh organic matter from inorganic raw material by producers. Rate of synthesis of organic matter by consumers. It is small & decreases with rise of trophic level. It is due to assimilation of food energy at consumers trophic level.

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