Given an ecosystem where a primary producer has a GPP of 6000 kJ/m²/year and respiration losses of 1500 kJ/m²/year, calculate the net primary productivity (NPP).

• A. 7500 kJ/m²/year
• B. 1500 kJ/m²/year
• C. 6000 kJ/m²/year
• D. 4500 kJ/m²/year

Answer: (D)