Overview
This lecture explains primary productivity in ecosystems, distinguishes between gross and net primary productivity, and discusses factors affecting productivity in various environments.
Primary Productivity Concepts
- Primary productivity is the amount of biomass or organic material produced by organisms, mainly via photosynthesis.
- Productivity depends on sunlight, water, and available plants converting solar energy into chemical energy like glucose.
- More plants and resources lead to higher productivity in an area.
Gross vs. Net Primary Productivity
- Gross Primary Productivity (GPP) is the total energy captured through photosynthesis in an ecosystem.
- Plants use some of this energy for cellular respiration (breaking down glucose to make ATP).
- Net Primary Productivity (NPP) is the remaining energy stored as biomass after subtracting energy used for respiration.
- NPP = GPP – Respiration (NPP is analogous to "net pay" after taxes).
Factors Affecting Productivity
- Rainforests have high NPP due to abundant water and sunlight; deserts have low NPP due to limited rainfall and plant life.
- Areas with higher NPP have more energy available for higher trophic levels, supporting greater biodiversity.
- Productivity is measured in kilocalories per square meter per year.
Productivity in Different Ecosystems
- Tropical rainforests, wetlands, and estuaries have high productivity.
- Productivity decreases in mountains and arid regions due to lack of plant life.
- Aquatic systems, especially oceans, contribute significantly to Earth's total productivity due to their vast size.
Light and Aquatic Productivity
- Aquatic productivity varies with depth: red light is absorbed quickly near the surface, while blue light penetrates deeper.
- Different organisms with varied pigments thrive at different water depths, affecting overall productivity.
Productivity Variations & Examples
- Forests have higher local NPP than open ocean, but oceans dominate global productivity.
- NPP decreases with depth in water and with seasonal changes in regions with fluctuating climate.
- Latitude, elevation, and seasons all influence primary productivity.
Practice Question Takeaway
- Student A is correct: Net primary productivity is low in deserts mainly due to low gross primary productivity from limited rainfall and photosynthesis.
Key Terms & Definitions
- Primary Productivity — Rate at which biomass is produced by photosynthetic organisms.
- Gross Primary Productivity (GPP) — Total energy captured by photosynthesis.
- Net Primary Productivity (NPP) — Energy remaining as biomass after subtracting respiration; NPP = GPP – Respiration.
- Respiration — Process where organisms break down glucose to release energy (ATP).
- Phytoplankton — Microscopic aquatic organisms that perform photosynthesis.
- Biomass — Total mass of living organisms in a given area.
Action Items / Next Steps
- Review section 1.9 for further understanding.
- Practice applying primary productivity concepts to different ecosystems.
- Ensure understanding of the differences between GPP and NPP.