Primary and Secondary Productivity

'The amount of organic matter or biomass produced by an individual organism, population, community or ecosystem during a given period of time is called productivity'.

Primary production refers to all or any part of the energy fixed by plants possessing chlorophyll. The total amount of solar energy converted (fixed) into chemical energy by green plants (by the process of photosynthesis) is called 'Gross Primary Production' (GPP).

The rate at which, organic matter is synthesized by producers per unit time and area is called 'Gross Primary Production' (GPP).

A certain portion of gross primary production is utilised by plants for maintenance (largely respiratory energy loss) and the remainder is called 'Net Primary Production (NPP)' which appears as new plant biomass.

Or

'The rate of organic matter build up or stored by producers in their bodies per unit time and area is called net primary production (NPP)'.

\GPP - Energy lost by respiration and maintenance = NPP

The biochemical formula that describes photosynthesis is,

Primary production is of special importance in ecology, since it is the energy fixed by plants by converting solar energy into chemical energy of food material that supports life in other trophic levels.

Secondary production refers to the net quantity of energy transferred and stored in the somatic and reproductive tissues of heterotrophs over a period of time.

Some heterotrophs (consumers and decomposers) feed on net

primary production and some on other heterotrophic organisms. Thus, productivity by hetertrophic organisms in the ecosystem is called secondary productivity.

Or

The rate of increase in the biomass of heterotrophs per unit time and area is called secondary productivity.

Secondary productivity serves as an index of significance of the population in terms of food resources available to the heterotrophic populations, including man, in the food chain.

Herbivores and carnivores ingest the food material where a part of this is assimilated and a part is egested. A large part of assimilated food (energy) is utilised for metabolism (largely respiration), growth, reproduction, maintenance of body and other activities. Remaining part is stored in somatic and reproductive tissues and thus compared to net production.

Secondary productivity by decomposer organisms (in a detritus food chain) is different. Here the matter is recycled and microorganisms show a high growth rate.

Community productivity is 'the rate of net synthesis or built up of organic matter by a community per unit time and area'.