The available biomass after respiration of producers and other...

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

A considerable amount of GPP is utilised by plants in respiration. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP).

$NPP = GPP - R$

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

Answer: Net primary productivity