Net Primary Productivity (NPP) — Definition, Formula, Examples

Gross Primary Productivity (GPP): The total rate of photosynthesis — the total energy fixed by producers from sunlight. This is the total organic matter produced.

Net Primary Productivity (NPP): The organic matter that remains after producers use some energy for their own cellular respiration.

Formula: NPP = GPP − Respiration (R)

Where:

• GPP = total energy fixed in photosynthesis
• R = energy used by plants/autotrophs for their own metabolic activities

Analogy: GPP is a factory's total revenue. Respiration is the factory's operating cost. NPP is the profit — what's left for others (consumers).

NPP varies widely across ecosystems:

Highest NPP (most productive):

1. Tropical rainforests: 1,000–3,500 g C m⁻² yr⁻¹ — high temperature, rainfall, and sunlight year-round.
2. Estuaries and swamps: 1,000–4,000 g C m⁻² yr⁻¹ — nutrient-rich shallow waters.
3. Coral reefs: high productivity due to algae.
4. Intensive agriculture (sugar cane, rice): modified for high productivity.

Moderate NPP: 5. Temperate forests and grasslands: 500–1,000 g C m⁻² yr⁻¹

Lowest NPP: 6. Deserts: <100 g C m⁻² yr⁻¹ — limited water 7. Open ocean: ~130 g C m⁻² yr⁻¹ — nutrient-poor 8. Tundra and polar regions: <100 g C m⁻² yr⁻¹ — cold, low light

Secondary Productivity: The rate of formation of new organic matter by consumers (animals, heterotrophs) from the organic matter they consume.

Note: Only NPP is divided into secondary productivity — the GPP consumed by producers' own respiration is completely lost as heat.

Flow of energy: Sunlight → GPP (photosynthesis) → [Respiration by plants] → NPP → Consumed by herbivores → Secondary productivity

This is why only about 10% of energy transfers to the next trophic level (10% law of Lindemann).