Productivity of Ecosystem  

The rate of biomass production is called productivity. It is expressed in terms of (gm–2)yr–1 or (k cal m–2) yr1 to compare the productivity of different ecosystems.

(i) Coral reefs, tropical rain forests, sugarcane fields are most productive.

(ii) Deserts and deep sea ecosystems are least productive.

Ecosystem productivity is maintained by the flow of energy derived from the sun.

Energy trapped by plants varies from ecosystem to ecosystem.

Table below shows energy absorption at different levels:

Types of productivity :

(i) Primary Productivity : The rate at which radiant energy is stored by photoautotrophs and chemoautotrophs.

a. Gross Primary Productivity (GPP) : It is the rate of organic matter synthesized by producers per unit area per unit time.

b. Net Primary Productivity. It is the rate of organic matter built up or stored by producers in their bodies per unit time and area. Net productivity is equal to gross primary productivity minus loss due to respiration and other reasons. NPP is the available biomass for the consumption to heterotrophs i.e. herbivores and decomposers.

Net primary productivity = Gross primary productivity – Respiratory loss.

Primary productivity depends on the plant species inhabiting a particular area, availability of nutrients and photosynthetic capacity of plants. This is available to herbivore level.

The annual NPP of whole biosphere is approximately 170 billion tons (dry wt.) of organic matter, despite occupying about 70% of the surface, the productivity of the oceans is only 55 billion tons.ln deep marine habitats, both light and nutrients become limiting. The most limiting nutrient of marine ecosystem is nitrogen.

(ii) Secondary productivity. Rate of increase in energy containing organic matter or biomass by heterotrophs or consumers per unit time and area is known as secondary productivity. It is available to carnivore level.

(iii) Community productivity. It is the rate of net synthesis of built up of organic matter by a community per unit time and area.

(iv) Ecological efficiency/Trophic level efficiency. The percentage of energy converted into biomass by a higher trophic level over the energy of food resources available at the lower trophic level is called ecological efficiency.