Question

What is Gross And Net primary Productivity and how it is calculated?

Answer 1

The amount of organic matter synthesized by producers per unit area in unit time is called Gross Primary Productivity.It refers to the total productivity including the energy utilized for respiration by the producers and depends on chlorophyll content.

The amount of organic matter stored by producers per unit area in unit time is called Net Primary Productivity.It refers to the net productivity that is converted to organic matter excluding the energy utilized for respiration by the producers and depends on chlorophyll content.

Answer 2

Gross primary production (GPP) is the total amount of energy produced by vegetation ; some of that energy is used for cellular respiration and maintainence of existing tissues (i.e."growth respiration and maintainence respiration").
Net primary production is the rate at which all the plants in an ecosystem produce net useful chemical energy; it is equal to the difference between the rate at which the plants in an ecosystem produce useful chemical energy (GPP) and the rate at which they use some of that energy during respiration. Some net primary production grows towards growth and reproduction of primary producers while some is consumed by herbivores.
To calculate net primary production , NPP= GPP- Respiration
To calculate gross primary production, GPP= NPP+Respiration