In which form can the productivity of ecosystems be compared?

Total energy fixed by an ecosystem is called

Assertion : Net primary productivity is gross primary productivity minus respiration.
Reason : Secondary productivity is produced by heterotrophs.

Secondary productivity is the rate of formation of new organic matter by:

$A$ is required for higher primary productivity. $B$ have the lowest primary productivity as the soil is deficient in moisture.
Choose the correct option for $A$ and $B$.

In a grassland ecosystem,which productivity $(g/m^2/yr)$ is the highest?