The mass of living material at a trophic level at a particular time is called

Standing crop refers to the amount of living biomass present in a particular trophic level at a given time. It is a measure of the amount of energy that is available to support higher trophic levels in an ecosystem.
(1) Net primary productivity (NPP) refers to the amount of energy that is available to support higher trophic levels after accounting for the energy that is lost to respiration by autotrophs.
(3) Gross primary productivity (GPP) refers to the total amount of energy that is fixed by autotrophs through photosynthesis. It is not a measure of the amount of living material at a trophic level, but rather
the total amount of energy that is fi axed by autotrophs through photosynthesis. 
(4) Standing state refers to the amount of nutrients, such as carbon, nitrogen, phosphorus, calcium etc., present in the soil at any given time.