The primary function of mycorrhizal fungi in ecosystems is to form beneficial symbiotic relationships with plant roots. These fungi help plants absorb essential nutrients like phosphorus and nitrogen from the soil, which enhances plant growth. In return, the plants provide the fungi with carbohydrates produced through photosynthesis. This mutualistic partnership significantly contributes to soil health and fertility, promotes plant diversity, and plays a crucial role in the stability of terrestrial ecosystems.