Is a white button mushroom a decomposer?

No, a white button mushroom (Agaricus bisporus) is not classified as a decomposer; it is primarily a saprotrophic fungus. While it does play a role in breaking down organic matter, it is cultivated for food rather than functioning exclusively in natural decomposition processes. Decomposers, like certain fungi and bacteria, primarily recycle nutrients by breaking down dead organic material in ecosystems.