Final answer:
The greatest difference in plant health between groups with and without mycorrhizae would be seen in soils deficient in mineral nutrients. Mycorrhizae significantly enhance nutrient uptake, especially in such poor soils, and provide protective benefits to plants.
Step-by-step explanation:
We would expect the greatest difference in plant health between two groups of plants of the same species, with one group having mycorrhizae and the other group without, in an environment where the soil is relatively deficient in mineral nutrients. Mycorrhizae are symbiotic associations between fungi and plant roots that are vital for plant health, particularly in nutrient-poor soils. They enhance the plant's ability to uptake nutrients like phosphate, zinc, and copper. Fungi benefit by receiving nutrients such as sugars from the plant. Especially when considering environments with poor soils, mycorrhizal fungi extend the root system's effective range by spreading hyphae beyond the nutrient depletion zone, hence showing more pronounced benefits in such conditions. In environments like those with nitrogen-fixing bacteria, the presence of mycorrhizae may not have as dramatic an effect on plant health since nitrogen fixation already provides a significant nutrient supply to plants. Similarly, regions with varying seasonal temperatures or those near bodies of water would not demonstrate as stark a contrast in plant health based on the presence of mycorrhizae alone, compared to the difference seen in nutrient-deficient soils. The importance of the mycorrhizal relationship is underscored by the fact that without these symbiotic fungi, a large percentage of trees and grasses would not survive, making mycorrhizae critical for the productivity of farmland. They also play a protective role by acting as a barrier to pathogens and may induce the plant's defense mechanisms.