Nutritional symbioses among soil organisms fascinate me. I study arbuscular mycorrhizas in natural and agricultural systems. A better understanding of the factors controlling the balance of trade between plants and mycorrhizal fungi could lead to their management so that fertilizer inputs can be reduced. Also, since mycorrhizal fungi are enormous (yet invisible), understanding how to manage them may help generate an important belowground carbon sink in our increasingly carbon dioxide enriched world.