Autotrophs:
Organisms that have light-harvesting pigments, trap solar energy and can make their own food are called autotrophs.
Heterotrophs:
Organisms that cannot make their own food and therefore depend upon other organisms (living or dead) are called heterotrophs.
Mushrooms as heterotrophs:
Mushrooms that belong to the kingdom of Fungi lack chlorophyll so they can not make their own food. They depend upon dead and decaying matter for nutrition hence, they are called heterotrophs and not autotrophs.