5.3.4 Gross Primary Production

Key Points

1. GPP:

• Measured as the energy input from photosynthesis in plants.
• It includes all the energy fixed, some of which will later be used for plant respiration.

2. Respiration (R):

• Plants use some of the energy from GPP to drive metabolic processes through respiration.

3. Net Primary Productivity (NPP):

• The energy remaining after respiration is called the Net Primary Productivity (NPP).
• This energy is available to herbivores and decomposers in the ecosystem.
• The relationship is summarised as:

$$\text{NPP} = \text{GPP} - \text{R}$$

Importance of GPP and NPP

• GPP represents the total energy input into an ecosystem via photosynthesis.
• NPP determines the energy available to the next trophic levels and thus influences the productivity of ecosystems.

Factors Affecting GPP

1. Light Intensity: More light increases photosynthesis and therefore GPP.
2. Temperature: Higher temperatures within a suitable range boost enzyme activity in photosynthesis.
3. Water Availability: Essential for photosynthesis and stomatal function.
4. Nutrient Availability: Nitrogen, phosphorus, and other nutrients are needed for plant growth.