In an ecosystem, the biomass that is actually available for...

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).

$\text{NPP} = \text{GPP} - \text{R}$

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

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

Standing state refers to the amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc., present in the soil at any given time.

Answer: Net primary productivity