What are mushrooms growing among grass are feeding on?

[wasteofo2]

Around my house, there are a lot of mushrooms growing amongst the grass, not on a fallen tree or anything. Obviously they're getting minerals and such from the ground, but where are they getting their organic molecules from? Are they like, feeding on the grass roots or something? Are there enough stray organic minerals in soil that mushrooms can just absorb those and live?

 

[loseyourname]

Fungi that grow on plant roots are known as mycorhizzae. The symbiosis between the fungus and the plant is mutualistic in nature; that is, both gain from the association. The fungus gets a largely stable environment due to the environmental regulation provided by the plant, and they also get their organic molecules from the plant (the answer to your question). The plant gets a hugely increased surface area for absoption of water and it gets inorganic molecules from the fungus, which is able to decompose them from organic waste, something the plant cannot do.