Primary Productivity
Primary productivity
Primary productivity is the rate of production of biomass using an external energy source and inorganic sources of carbon and other elements.
- Primary productivity refers to the rate of production of biomass in an ecosystem using an external energy source (such as sunlight or chemical energy) and inorganic carbon and nutrients.
- It measures how effectively producers, mainly plants and algae, convert inorganic materials into organic compounds that sustain all life in the ecosystem.
- It is measured in kg carbon m⁻² year⁻¹, meaning kilograms of carbon fixed per square metre per year.
- It forms the foundation of energy flow in ecosystems, as all consumers depend on the organic matter created by producers.
- Tropical rainforests have high primary productivity because of abundant sunlight, warmth, and rainfall.
- Deserts have low productivity due to limited water availability.
Factors Affecting Primary Productivity
- Light availability: More sunlight increases photosynthesis.
- Temperature: Warm temperatures enhance enzyme activity in plants.
- Water availability: Adequate rainfall supports continuous growth.
- Nutrient supply: Nitrogen and phosphorus availability control productivity.
- Carbon dioxide concentration: Influences photosynthetic rate.
- Type of ecosystem: Aquatic ecosystems often depend on nutrient availability while terrestrial ones depend on temperature and precipitation.
Deserts have low productivity due to limited rainfall, while estuaries have high productivity because of shallow waters, sunlight, and nutrient-rich sediments.
Methods for Measuring Primary Productivity
1. Laboratory-Based Methods
- Used for aquatic or small-scale plant samples.
- Involves measuring the rate of photosynthesis using oxygen output or CO₂ consumption.
- Samples of algae or aquatic plants are placed under light and dark conditions to compare O₂ changes.
2. Field-Based Methods
- Used for terrestrial ecosystems such as grasslands or forests.
- Involves measuring biomass changes over time.
- Dry biomass is measured at the start and end of a period, and the difference indicates productivity.
- Non-destructive tools like optical sensors or remote sensing can be used for large areas.
- Always include units (kg C m⁻² yr⁻¹) when describing productivity.
- These units standardize comparison between ecosystems.
Secondary productivity
Secondary productivity
Secondary productivity refers to the gain in biomass by consumers (such as herbivores, carnivores, and omnivores) through the assimilation of carbon compounds from the food they ingest.
- Secondary productivity depends on how efficiently consumers digest, absorb, and convert energy from their food.
- It measures the energy or biomass accumulated per unit area per unit time.
- Units are the same as for primary productivity - kg carbon m⁻² yr⁻¹.
- Energy losses occur through faecal waste, respiration, and metabolic heat.
Net Primary Productivity (NPP)
Net primary productivity
Net Primary Productivity (NPP) refers to the amount of carbon that is captured by plants through photosynthesis and is available for growth and reproduction after subtracting the energy used by the plants for cellular respiration.
- Net primary productivity (NPP) is the basis for food chains, representing the amount of biomass available to primary consumers after subtracting the energy used by producers for respiration.
- It is the energy remaining in plants that can be consumed sustainably by herbivores or harvested by humans in agriculture and forestry.
- NPP determines the carrying capacity of an ecosystem, the amount of life it can support.
In a meadow ecosystem, NPP corresponds to the new plant growth that herbivores can feed on without depleting resources.
Tip- When explaining NPP, always link it to the energy available to the next trophic level.
- It shows the foundation of all energy flow in an ecosystem.
Maximum Sustainable Yield (MSY)
Maximum sustainable yield
Maximum sustainable yield (MSY) is the largest amount of biomass that can be harvested from an ecosystem without depleting its resources, ensuring long-term sustainability.
- Maximum Sustainable Yield (MSY) is the largest harvest rate that can be taken from a population or ecosystem without reducing its capacity to regenerate.
