Nitrogen is a limiting nutrient for

Options

A. natural ecosystem
B. aquatic acosystem
C. agricultural ecosystem
D. both a and c

Answer

### Step-by-Step Solution:

1. **Understanding Nitrogen's Role**:
- Nitrogen is an essential element for living organisms. It is a crucial component of proteins and DNA, which are fundamental for growth and development.

2. **Defining Limiting Nutrient**:
- A limiting nutrient is defined as a nutrient that is present in short supply. When a nutrient is in limited availability, it restricts the growth and development of organisms.

3. **Identifying Ecosystems**:
- We need to evaluate different ecosystems to determine where nitrogen acts as a limiting nutrient.

4. **Evaluating Natural Ecosystem**:
- In natural ecosystems, nitrogen is often found in low quantities, making it a limiting nutrient. Therefore, nitrogen limits the growth of organisms in these ecosystems.

5. **Evaluating Aquatic Ecosystem**:
- In aquatic ecosystems, nitrogen is generally not in short supply. Thus, it does not act as a limiting nutrient in these environments.

6. **Evaluating Agricultural Ecosystem**:
- In agricultural ecosystems, nitrogen is frequently used up by crops and can be in short supply. Therefore, it is also a limiting nutrient in agricultural settings.

7. **Conclusion**:
- Based on the evaluations, nitrogen is a limiting nutrient in both natural ecosystems and agricultural ecosystems, but not in aquatic ecosystems.

### Final Answer:
- Nitrogen is a limiting nutrient for **Natural Ecosystems (A)** and **Agricultural Ecosystems (C)**.

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