Highest value in g/m${}^2$/yr of a grassland ecosystem would be

Productivity is rate of accumulation of energy containing organic matter by an ecosystem per unit area per unit time. It is of two types primary and secondary. Productivity at producers level is known as primary productivity. It is two types. Gross primary productivity is primary productivity including that amount which is utilized in respiration and other metabolic activities. Net primary productivity (NPP) is primary productivity in excess to that which is utilized in respiration and other metabolic activities. Secondary productivity is productivity at consumers level. Since, gross production includes total production including the amount utilized in respiration and other metabolic activities so it is more than other forms of productivity.