Describe the role of mycorrhizal fungi in soil.

Mycorrhizal fungi play a crucial role in forming symbiotic relationships with plant roots, which is why this answer is the most accurate. In this association, the fungi colonize the root systems of plants, enhancing the plant's nutrient and water uptake capabilities. The fungi extend the root network into the soil, allowing plants to access nutrients such as phosphorus and nitrogen that are often out of reach for plant roots alone. In exchange, the plants provide carbohydrates and other organic substances to the fungi, creating a mutually beneficial arrangement that supports plant growth and health.

This relationship is particularly vital in nutrient-poor soils, where mycorrhizal fungi help improve soil structure and increase the resilience of plants against environmental stresses. The presence of mycorrhizal fungi not only boosts individual plant health but also contributes to the overall biodiversity and stability of the ecosystem. Therefore, their role in forming these symbiotic relationships is fundamental to soil ecology and plant nutrition.