Overview
This lecture covers primary productivity, focusing on how solar energy is converted into chemical energy by plants, and explains factors that influence productivity and its relationship to biodiversity.
Primary Productivity Basics
- Primary productivity is the rate at which solar energy is converted into organic compounds (like glucose) through photosynthesis.
- It is usually measured in kilocalories per square meter per year (kcal/m²/yr).
- Higher primary productivity leads to greater plant growth and more food/shelter for animals, increasing biodiversity.
Components of Productivity
- Plants use some captured energy for cellular respiration (energy needed for basic life processes).
- Gross Primary Productivity (GPP): total amount of sunlight captured and converted into energy via photosynthesis.
- Net Primary Productivity (NPP): energy remaining after respiration, stored as plant biomass and available to consumers.
- NPP = GPP – Respiration Loss.
Ecological Efficiency
- Ecological efficiency refers to the proportion of incoming sunlight converted into biomass by plants.
- Only about 1% of incoming sunlight is captured by plants, and about 0.4% is stored as NPP.
- Most sunlight is either reflected or passes through leaves, not used in photosynthesis.
Trends and Factors Affecting Productivity
- More productive ecosystems support higher biodiversity due to abundant plant life.
- Factors increasing productivity: high water availability, warm temperatures, and high nutrient availability.
- Highly productive biomes: swamps, marshes, tropical rainforests, coral reefs (abundant water, warmth, nutrients).
- Low productivity biomes: deserts (lack water/nutrients), tundra (cold/limited liquid water), open ocean (low nutrients).
Key Terms & Definitions
- Primary Productivity — rate of solar energy conversion to organic compounds via photosynthesis.
- Gross Primary Productivity (GPP) — total sunlight energy captured by plants.
- Net Primary Productivity (NPP) — energy stored in plant biomass after respiration.
- Respiration Loss — energy used by plants for living functions.
- Ecological Efficiency — percentage of incoming energy captured and stored as biomass.
Action Items / Next Steps
- Practice describing the process of net primary productivity.
- Describe the relationship between primary productivity and biodiversity.
- Review which factors drive high or low productivity in biomes.