We would expect the greatest difference in plant health between two groups of plants of the same species, one group with mycorrhizae and one group without mycorrhizae, in an environment

Options

A. where nitrogen-fixing bacteria are abundant.
B. that has soil with poor drainage.
C. that has hot summers and cold winters.
D. in which the soil is relatively deficient in mineral nutrients.

Answer

To determine the environment where the greatest difference in plant health would be observed between two groups of the same species—one with mycorrhizae and one without—we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Mycorrhizae**:
- Mycorrhizae are symbiotic fungi that associate with plant roots. They enhance nutrient uptake, particularly phosphorus and nitrogen, which are essential for plant growth.

2. **Role of Mycorrhizae in Nutrient Uptake**:
- The hyphae of mycorrhizae increase the surface area for absorption, allowing plants to access more nutrients from the soil. This is particularly beneficial in nutrient-deficient environments.

3. **Identifying the Right Environment**:
- We need to consider environments where nutrient availability is limited. In such cases, the presence of mycorrhizae would significantly improve the health and growth of plants compared to those without mycorrhizae.

4. **Evaluating the Options**:
- **Option 1**: Environments with abundant nitrogen-fixing bacteria. Here, the difference may not be significant because nitrogen-fixing bacteria can provide nitrogen, which could mask the benefits of mycorrhizae.
- **Option 2**: Soil with poor drainage. This does not specifically relate to nutrient availability and may not show a significant difference.
- **Option 3**: Environments with hot summers and cold winters. This option does not directly address nutrient availability.
- **Option 4**: Soil that is relatively deficient in mineral nutrients. In this scenario, the presence of mycorrhizae would be crucial for nutrient uptake, leading to a noticeable difference in plant health.

5. **Conclusion**:
- The environment where we would expect the greatest difference in plant health between the two groups is one that is relatively deficient in mineral nutrients. In such an environment, the plant with mycorrhizae (Group A) would show significantly better growth and health compared to the plant without mycorrhizae (Group B).

### Final Answer:
The greatest difference in plant health between two groups of the same species, one with mycorrhizae and one without, would be expected in an environment that is relatively deficient in mineral nutrients.