Net primary production (NPP) = GPP – R, where R represents respiratory losses to the environment
Plants use some of their captured energy for their own respiration. Net primary production (NPP) is the energy that remains after subtracting those respiratory losses from the total energy fixed.
Formula
NPP = GPP − R
Real World
A UK wheat field fixes roughly 22 000 kJ m⁻² year⁻¹ through photosynthesis (GPP), but the crop respires away about 11 000 kJ m⁻² year⁻¹, leaving an NPP of around 11 000 kJ m⁻² year⁻¹ available for grain production.
Exam Focus
In calculation questions, clearly define R as plant respiratory losses only — do not include consumer or decomposer respiration.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
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