Net Primary Production (NPP) is the energy remaining in plants after respiration losses (R) have been subtracted from the Gross Primary Production (GPP). This energy is stored as biomass and is available for growth, reproduction, and consumption by other trophic levels, such as herbivores and decomposers.

Key Points

1. NPP Formula:

• GPP: Total energy fixed during photosynthesis.
• R: Energy lost during respiration.

2. Uses of NPP:

• Supports plant growth (e.g., formation of leaves, stems, and roots).
• Fuels reproductive processes (e.g., production of flowers, seeds, or fruit).
• Provides energy to consumers in the ecosystem, forming the base of food chains.

3. Units of Measurement: NPP is measured as energy per unit area per unit time, often expressed as:

• $kJ\ m⁻² \ year⁻¹$ (kilojoules per square metre per year).

Exam Tip

Be prepared to calculate NPP using the formula and interpret its significance in energy transfer questions. Always connect NPP to ecosystem productivity and food chain dynamics when explaining its role.