The rate of generation of biomass in an ecosystem is called Productivity, which is expressed in units of energy (example: joules per meter² per day) or in units of dry organic matter (example: kg per meter² per year).
Primary production is the synthesis of new organic material from inorganic molecules such as water and CO2 via photosynthesis or chemosynthesis. The rate at which radiant energy is stored by photosynthetic and chemosynthetic activity of producers is called primary productivity.
Further, the total energy fixed by plants via photosynthesis is called Gross Primary Productivity. A small fraction of this energy fixed is used in the respiration of plants, which gives them necessary energy for various physiological and morphological functions. When this respiratory utilization is reduced from Gross Primary Productivity, what we get is Net Primary Productivity. Net Primary Productivity is the actual rate of biomass productivity, which refers to the balance between gross photosynthesis and respiration and other plant losses. The primary productivity is also known as energy storage at producer level.
Highest Net Primary Productivity of Various Ecosystems
Kindly note that highest primary productivity is found in Tropical Forests, Estuaries and Swamps/ Marshes. Each of them produces around 9000 Kcal per meter² per year.
- Tropical Rainforests have high primary productivity because of availability of plenty of solar light and water.
- A typical estuary has high primary productivity because it is shallow (gets plenty of sunlight) and has turbulent water (which brings the nutrient rich material from sea bed).
- Swamps and Marshes have high primary productivity because they have lots of nutrients and sunlight.
After Tropical Rainforests, Estuaries and Swamps / Marshes, the highest primary productivity is found in coral reefs, algal beds and temperate forests. Least primary productivity is found in cold and hot deserts including tundra.
Productivity of heterotrophs such as animals is called secondary productivity. It is also known as energy storage at consumer level. Secondary productivity is done by consumers via assimilation of the food they take. Since not all the primary biomass is consumed; and since not all the consumed is digested; secondary production is only a fraction of primary production.