How are productivity, gross productivity, net primary productivity and secondary productivity interrelated.

Productivity is the rate of biomass production expressed in terms of g$(-2)$ yr$(-1)$ or kcal m$(-2)$. Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period, all during photosynthesis.

Gross primary productivity (GPP) of an ecosystem is defined as the rate of production of organic matter or biomass during photosynthesis.

Net primary productivity (NPP) is GPP minus respiration loses (R), in the equation, written as NPP = GPP - R

Secondary productivity is given by the rate of formation of new organic matter by the consumers.

Hence, all are interrelated as mentioned above.