In habitats with limited nutrients, certain fungus species grow on the roots of trees, engaging in mutually beneficial relationships known as ectomycorrhizae: in this symbiotic exchange, the tree provides the fungus with carbon, a nutrient necessary for both species, and the fungus _______ by enhancing the tree's ability to absorb nitrogen, another key nutrient, from the soil.

Which choice completes the text with the most logical and precise word or phrase?