Answer:
Primary productivity is 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 is of
two types: gross primary productivity and net primary productivity. Gross
primary productivity of an ecosystem is the rate of production of organic
matter during photosynthesis. Gross primary productivity minus respiration
losses (R), is the net primary productivity (NPP).
Factors affecting
primary productivity:
(i) Solar radiation:
Maximum light is available in tropics. Poles receive minimum light. Due to
this, photosynthesis is maximum and net primary productivity (NPP) is highest
(> 20 t 
)
in tropics against (about 8 t )
in temperate forests.
(ii) Temperature:
Temperate forests have lesser productivity than tropical rain forests due to
cold climate.
(iii) Moisture: Rain
and humidity increase productivity of the ecosystem.
(iv) Nutrients:
Nutrients are essential for producers? growth. Desert soils are deficient in
nutrients and therefore, are less productive.
(v) Photosynthetic
efficiency of producers: 
plants are
more productive than 
plants.
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