Functions of Ecosystem: Productivity - Practice Questions & MCQ

• The rate of biomass production is called productivity.

Primary Productivity:

• Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. 
• It is expressed in terms of weight  or energy .
• It can be divided into: 
  • Gross primary productivity (GPP) 
  • Net primary productivity (NPP)
• The total solar energy trapped in the food material by photosynthesis is referred to as gross primary productivity (GPP).
• However, a good fraction of gross primary productivity is utilised in respiration of green plants.
• Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP):

• Net primary productivity is the available biomass for the consumption of heterotrophs (herbivores and decomposers).

Secondary Productivity:

• Secondary productivity is defined as the rate of formation of new organic matter by consumers.

Standing Crop:

• This is the abundance of organisms existing in the area at any one time. I
• t may be expressed in terms of number of individuals, as biomass of organisms, as energy content or in some other suitable terms. 
• Measurement of standing crop reveals the concentration of individuals in various populations of the ecosystem.

Environmental Factors Affecting the Productivity in Ecosystem:

• Solar radiation and temperature.
• Moisture, i.e., leaf water potential, soil moisture, fluctuation of precipitation, and transpiration.
• Mineral nutrition, i.e., uptake of minerals from the soil, rhizosphere effects, fire effects, salinity, heavy metals and nitrogen metabolism.
• Biotic activities, i.e., grazing, above ground herbivores, below ground herbivores, predators and parasites and diseases of primary producers.
• Impact of human populations, i.e., populations of different sorts, ionising radiations, such as atomic explosions, etc.
• In aquatic systems, productivity is generally limited by light, which decreases with increasing water depth. 
• In deep oceans nutrients often become limiting for productivity. Nitrogen is the most important nutrient limiting productivity in marine ecosystems.