Primary productivity is expressed in terms of

Options

A. `(Kcal m^(-2))yr^(-1)`
B. `("Kcal" xx "yr")/(m^2)`
C. `yr //gm^2`
D. `("Kcal")/(m^2)`

Answer

**Step-by-Step Solution:**

1. **Understanding Primary Productivity**:
- Primary productivity refers to the rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances. It is essentially the fixation of solar energy by plants.

2. **Types of Primary Productivity**:
- There are two main types of primary productivity: Gross Primary Productivity (GPP) and Net Primary Productivity (NPP).
- **Gross Primary Productivity (GPP)**: This is the total amount of energy that is captured by plants through photosynthesis.
- **Net Primary Productivity (NPP)**: This is the energy that remains after accounting for the energy used by plants for respiration. It is calculated as GPP minus the energy lost to respiration.

3. **Measurement Units**:
- Primary productivity is typically measured in terms of energy per unit area per unit time. The common units used are kilocalories per square meter per year (kcal/m²/yr).

4. **Factors Affecting Productivity**:
- Various factors such as solar radiation, water availability, and nutrient levels influence the productivity of different ecosystems. For instance, deserts and tundras have low productivity, while estuaries and marshes are highly productive.

5. **Conclusion**:
- Therefore, primary productivity is expressed in terms of kilocalories per square meter per year (kcal/m²/yr).

**Final Answer**: Primary productivity is expressed in terms of kilocalories per square meter per year (kcal/m²/yr).

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