Ch.31 - Fungi Study Notes on Fungi and Their Ecological Importance

Fungi are crucial decomposers in ecosystems.
- They decompose approximately 50% of all organic matter, including corpses and trees.
- Bacteria account for about half of decomposition, while fungi are responsible for the other half.
Nutrient Release and Plant Growth
- Fungi help in breaking down organic materials (e.g., logs) to release essential nutrients like nitrogen, phosphorus, calcium, etc. back into the soil.
- These nutrients are vital for plant growth.
Symbiotic Relationships
- Fungi form symbiotic relationships with various species.
- One example includes fungi providing benefits to plants in exchange for sugars produced via photosynthesis.
- Key examples of symbiotic relationships:
- Mycorrhizal fungi: Form associations with plant roots to enhance water and nutrient absorption.
- Lichens: Create a symbiotic relationship between fungi and algae (or cyanobacteria).

Molds
- Defined as fast-growing, usually asexually dividing fungus colonies.
- Examples include black molds, red molds, and blue-green molds (e.g., on oranges).
- Not a taxonomic category but rather a lifestyle of fungi.
Yeasts
- Single-celled fungi, commonly found in various environments.
- Example: Yeast used for baking bread, showcasing their importance in culinary applications.
Lichens
- Symbiotic organisms composed of a fungus and a photosynthetic partner (e.g., green algae or cyanobacteria).
- Types of lichens include:
- Crustose lichens: Flattened against surfaces (e.g., rocks).
- Foliose lichens: Leafy structure.
- Fruticose lichens: Highly branched.

Mycorrhizal fungi and plants have a mutually beneficial relationship.
- Fungi help plants absorb more nutrients and water through expanded root systems.
- Plants provide carbohydrates (sugars) produced via photosynthesis to the fungi.
Types of Mycorrhizal Fungi
- Ectomycorrhizae: Fungi that coat the outside of plant roots.
- Endomycorrhizae: Fungi that invade plant roots with specialized structures called haustoria, allowing direct nutrient exchange.
Importance of Mycorrhizal Fungi
- Approximately 90% of plants engage in a mycorrhizal association.
- Improved growth observed in plants with mycorrhizal fungi, indicating notable advantages in resources and health compared to non-mycorrhizal counterparts.

Fungi play critical roles in various ecosystems beyond decomposition:
- Fungus-farming ants cut leaves and use them to cultivate fungi, providing a food source for the ants.
- Fungi assist in breaking down cellulose in the guts of herbivorous animals (e.g., cows and termites), facilitating digestion and energy extraction.
Disease and Parasitism
- Some fungi, like corn smut (an Ascomycetes), can severely impact agricultural crops by obliterating them.
- Ergot fungi can infect wheat and rye, producing psychoactive compounds if ingested through contaminated bread.
- Other plant diseases, such as tar spot fungus, can reduce overall productivity in affected trees, including those used for maple syrup.
- Approximately 30% of fungal species are known plant parasites, but this is not the majority.

Animal Parasites
- Chytrids, a group of fungi, can cause skin infections in amphibians, contributing to population declines.
Human Fungal Infections
- Common infections include athlete's foot and ringworm, both caused by ascomycete fungi.
- Coccidioidomycosis is a more severe lung infection often affecting immunocompromised individuals, resembling pneumonia.

Fungi produce antibiotics, such as penicillin, that have significant medical applications.
They are utilized in the production of bread, beer, and other fermentation processes.
Fungal species are also crucial in molecular biology research and have various practical applications.
Conclusion:
- The vast majority of fungi contribute positively to ecosystems and human endeavors.
- Not all fungi are harmful; many support life as we know it today.
Questions and discussion points brought up towards the end of the session.