- The rate of biomass production in an ecosystem is called its productivity.
- or energy captured per unit area of land, per unit time.
- It is generally expressed in terms of g/m-/year, or kcal/m-/year. Hence, the
- productivity of different ecosystems can be easily compared.
- Productivity in ecosystems is of two kinds, primary and secondary.
(i) Primary Productivity
- It refers to the rate at which sunlight is captured by producers for the synthesis of
- energy-rich organic compounds through photosynthesis. Primary productivity
- has two aspects, gross and net.
- The rate of total capture of energy, or the rate of total production of organic
- material (biomass), is known as gross primary productivity.
- But during energy production (photosynthesis) a large amount of energy 1s
- consumed in other vital processes likee respiration and transpiration etc. Dueo
- this the net amount of energy becomes lesser. This value is called Net primary productivity.
(ii) Secondary Productivity
When food is utilized by consumers, the energy assimilation process occupies again, in their body. At the trophic level of consumers, the rate at which food energy is assimilated is called secondary productivity. (Students should note that the food of consumers is produced by the primary producers. Therefore, the secondary productivity reflects only the utilisation of this food for the production of consumer biomass).
Net productivity = Gross productivity energy consumption in respiration and other vital processes
- The net primary productivity results in the accumulation of plant biomass which serves as the food of herbivores and decomposers.
- The magnitude of primary productivity depends on the photosynthetic capacity of producers and the prevailing environmental conditions, particularly solar
- radiation, temperature and soil moisture.
- In tropical regions, primary productivity may be sustained throughout the year, provided adequate soil moisture remains available. However, in temperate Tegions, primary productivity is severely limited by cold climate and a short snow free growing period during the year.
- In aquatic ecosystems, productivity is generally limited by light, which decreases with increasing water depth.
- In general, the primary productivity of tropical rain forest is maximum, whereas that of deserts is minimum.