Water, ph, and temperature

Fungi require water for nutrient uptake and they are therefore restricted to fairly moist environments such as host tissue if they are parasites or symbionts, or soils and damp substrates if they are saprophytes. Desiccation causes death unless the fungus is specialized, as they are in the lichens. Some fungi are wholly aquatic.

Fungi tend to occupy acidic environments and by their metabolic activity tend to further acidify them. They grow optimally at pH 4–6. Most fungi are mesophilic, growing at between 5^? and 40^?C. Some are psychrophilic and are able to grow at under 5^?C, others are thermotolerant or thermophilic and can grow at over 50^?C.