Substrate

In mycology, the term "substrate" refers to the physical base (material) on or inside which a fungus grows, and from which it gets nutrients and water.

Unlike plants, which can grow on almost any soil given sunlight, fungi are extremely picky about their substrate. Their digestive enzymes are tuned to break down very specific chemical compounds.

Ecological specialization

As David Arora notes, you won't find a mushroom that feeds on oak wood on a pine stump or in meadow soil. Fungi are strictly specialized by substrate type:

1. Soil-dwelling (terrestrial): They grow on bare ground, sand or among grass. Most often these are mycorrhizal mushrooms (porcini, chanterelles) whose mycelium is connected to tree roots underground.

2. Litter-dwelling (lignophilous/humus): Their substrate isn't the soil itself but the layer of fallen leaves, needles or moss on top of it. They are saprotrophs that turn litter into humus (brittlegills, bonnets).

3. Wood-dwelling (xylotrophs): They live only on wood (honey fungus, oyster mushrooms, bracket fungi). They divide into those that eat dead stumps (saprotrophs) and those that attack living trees (parasites).

4. Extreme substrates: Some fungi have chosen places to live where they have no competitors. For example, burnt ground (charcoal), animal droppings (dung) or even anthills.

Correctly identifying the substrate you found a mushroom on is 50% of the way to identifying it accurately.

Sources

1.Зерова М.Я. та ін. Визначник грибів України. 1979
2.Roger Phillips. Mushrooms (Roger Phillips)
3.David Arora. Mushrooms Demystified
4.Index Fungorum