The correct option is C Gross primary productivity
In an ecosystem, the rate of formation of organic matter during photosynthesis is termed as gross primary productivity.
Net Primary Productivity (NPP) /net productivity, or the production of plant biomass, is equal to all of the carbon taken up by the vegetation through photosynthesis (called Gross Primary Production or GPP) minus the carbon that is lost to respiration.
The rate at which these consumers convert the chemical energy of their food into their own biomass is called secondary productivity.