In a deciduous forest ecosystem, mushroom would be a decomposer.
A decomposer is an organism that breaks down decaying organic material. Decomposers obtain their energy by ingesting the organic material they are decomposing. Mushroom (a decomposer) is a fungus that release enzymes which decompose dead plants and animals. Mushroom can be found in a deciduous forest ecosystem (an ecosystem that contains mainly broad-leaved trees whose leaves fall during one season).