Color-enhanced light micrograph of Mycorrhizal root cells, showing arbuscules (dark lines) inside cortical root cells of a corn plant. Arbuscules are the finely branched structures of fungi found in the roots of plants. The plant roots and fungus form a symbiotic (mycorrhizal) relationship. Arbuscular mycorrhizal (AM) fungi help plants to capture nutrients, such as phosphorus, and micronutrients from the soil, exchanging them for carbon. This is one mechanism by which carbon dioxide from the air is drawn into the soil.