Fungi are a diverse group of organisms that form their own biological kingdom. They are eukaryotic and acquire nutrients by absorbing dissolved molecules, often by secreting digestive enzymes. Their cell walls are made of chitin. Fungi are found in almost every corner of the planet, demonstrating remarkable adaptability.
Fungi in Terrestrial Ecosystems
Terrestrial environments host a wide variety of fungal species. Fungi break down dead or decaying organic matter, such as fallen leaves and wood, returning essential nutrients to the soil. This process is important for the carbon cycle, as fungi release carbon, nitrogen, and phosphorus. Visible mushrooms are often just the fruiting bodies of extensive fungal networks, called mycelia, hidden beneath the surface.
Many fungi form mutually beneficial relationships with plants, particularly in the soil. Mycorrhizal fungi associate with plant roots, expanding the plant’s ability to absorb water and nutrients. In return, the plant provides the fungus with sugars. Two main types exist: ectomycorrhizae, which form a sheath around the root, and endomycorrhizae, which penetrate root cells. Examples include truffles with oak or beech trees, and boletes with conifers.
Another terrestrial partnership involves lichens, composite organisms formed by a fungus living with algae or cyanobacteria. The fungal partner provides structure and absorbs moisture and minerals. The algae or cyanobacteria produce organic carbon compounds through photosynthesis, supplying food. Lichens are often seen as crusts on rocks and tree bark, thriving where neither partner could easily survive alone.
Fungi in Aquatic Environments
Fungi are abundant in aquatic ecosystems, including freshwater and marine habitats. In freshwater environments like lakes and rivers, fungi decompose organic matter such as submerged leaves and dead animals. Aquatic hyphomycetes break down plant debris, contributing to nutrient cycling and supporting the food web. Some aquatic fungi also act as parasites, infecting phytoplankton and zooplankton.
Marine fungi are found in oceanic environments, from coastal waters to deep-sea sediments. Most marine fungi are microscopic, though marine lichens can be visible. These fungi recycle organic matter by degrading materials like wood and seaweed. They also form symbiotic relationships with other marine life, including corals and sponges.
Marine fungi adapt to salty surroundings, coping with high salinity and pressure. Some species are obligately marine, growing exclusively in seawater, while others are facultative, living in both terrestrial and marine environments. They play a role in nutrient cycling and can degrade pollutants like hydrocarbons.
Fungi and Other Living Organisms
Fungi form close associations with other living organisms, extending their habitats beyond soil and water. These interactions can be mutualistic, where both benefit, or parasitic, where one benefits at the other’s expense. Many insects have mutualistic relationships with fungi; leaf-cutter ants cultivate “fungus gardens,” feeding on the fungi they grow. Some scale insects are protected by fungal mycelium, which covers their colonies while the fungi obtain nutrients.
Fungi also inhabit the digestive tracts of herbivores, such as ruminants, where anaerobic fungi help break down tough plant materials. This internal environment provides a stable habitat and constant food supply. These gut fungi contribute to the host’s nutrition by making complex carbohydrates more accessible.
Fungi can also be parasites, causing diseases in plants, animals, and humans. In plants, fungal pathogens can destroy tissues and spoil crops, leading to economic losses. Examples include rusts and smuts on cereal crops, or molds causing decay in fruits. For animals and humans, fungal infections can range from superficial skin conditions like athlete’s foot to more serious systemic diseases. Some fungi produce toxins, such as aflatoxins, which can cause illness.
Fungi in Unexpected and Extreme Habitats
Fungi demonstrate resilience, inhabiting surprising or hostile environments. Fungal spores are ubiquitous in the atmosphere, traveling through air currents and settling in new locations. They allow fungi to reproduce and disperse widely, influencing air quality and potentially impacting human health through allergens.
Human-made environments also serve as habitats for various fungi. Molds frequently grow in homes, particularly in damp areas like bathrooms or basements, on surfaces such as carpets and walls. In food production, yeasts are used for fermentation, playing a role in making bread rise and producing alcoholic beverages. Certain molds ripen cheeses, contributing to their distinct flavors.
Some fungi are extremophiles, thriving in conditions considered extreme. These include fungi in highly radioactive areas, like the Chernobyl exclusion zone, where some species use radiation as an energy source. Other fungi tolerate extreme temperatures or survive in environments with high salinity. Some fungal species degrade polymers like plastic and hydrocarbons, showing their potential for bioremediation.