Getting To Know Fungi

Introduction

Fungi are an important part of your microbiome ecology. The majority of fungi decompose the lignin and the hard-to-digest soil organic matter, but some fungi consume simple sugars. Fungi dominate in low pH or slightly acidic soils where soils tend to be undisturbed (Lavelle & Spain, 2005). Fungi break down the organic residues so that many different types of microbes can start to decompose and process the residues into usable products. 

Approximately 80 to 90 percent of all plants form symbiotic mycorrhizae fungi relationships by forming hyphae networks. The hyphae are much smaller than most plant root hairs and assist the plant in acquiring nitrogen, phosphorus, micronutrients and water in exchange for sugar produced by the plant. This mutually beneficial relationship is called a mycorrhizae network and is essential for plant production. (Magdoff & Van Es, 2009). 

Hyphae interact with soil particles, roots, and rocks forming a filamentous body that promotes foraging for soil nutrients. These networks release enzymes into the soil and break down complex molecules that the filaments then reabsorb. Fungi act like natural recycling bins, reabsorbing and redistributing soil nutrients back to plant roots. Most hyphae are either pure white or yellow and are often misidentified as plant hair roots (Islam, 2008).

Fungi prefer slightly acidic conditions, low disturbance soils, perennial plants, internal nutrient sources directly from the plant, and highly stable forms of organic residues with high carbon to nitrogen (C:N) values and slower recycling time. 

This allows fungi to bridge gaps in the soil so as to transport nutrients relatively far distances back to the plants (Lowenfels & Lewis, 2006).

Fungi Classification

There are four major groups of soil fungus: Zygomycota, Ascomycota, Basidiomycota, and Deuteromycota. 

Zygomycota 

There are less than 1,000 species of zygomycota and they are mostly common bread molds. 

Ascomycetes

There are about 30,000 species and are mostly yeasts used in baking. Ascomycetes fungi are microscopic in size and dominate in agricultural soils and grasslands.

Basidiomycetes

These  include most mushrooms, toadstools and puffballs and are often seen above ground.  Basidiomycetes have large fruiting bodies or mushrooms that dominate in high residue and forested soil (Dick, R., 2009).

Deuteromycota 

This group includes the lichens and the mycorrhizal fungus important in nutrient exchange  (Biological Diversity: Fungus, n. d.; Lavelle & Spain, 2005).

Dynamics of the Fungal Family

Fungi are classified as heterotrophs so the carbon source originates from the decomposition of organic compounds or residues (Sylvia et al., 2005).

Decomposers 

Also called saprophytic fungi, they decompose cellulose and lignin (tough plant fibers) in the soil. Zygomycetes (bread molds) consume exclusively sugar but most fungi decompose the more recalcitrant or hard-to-decompose organic residues high in plant fiber content (complex sugars). Some of the byproducts of this decomposition may turn to humus and remain in the soil for thousands of years (Ingham, 2009; Lavelle & Spain, 2005; Lowenfels & Lewis, 2006). 

Pathogens

These can cause many agricultural root diseases including Phytophthora, Rhizoctonia, Pythium, and Verticillium, and downy mildew. Some fungi help to control diseases and predators including a nematode trapping fungi that feeds on insects and can be used as biological controls. 

Mutualistic

 Mycorrhizal fungi form a beneficial relationship with plants. Mycorrhizae grow within the root cells and are commonly associated with grasses, row crops, vegetables, and shrubs. 

Backyard Fungi Ecology

Many plants have a preferred fungus to bacteria ratio (F:B ratio) and cultivate certain species of both bacteria and fungus to increase nutrient extraction from the soil.

Fig 1. Fungi to Bacteria Ratio for Given Plant Type

                                      *(Lowenfels & Lewis, 2006). 

Why Fungi Matters

Fungi benefit most plants by suppressing plant root diseases and by attacking plant pathogens with fungal enzymes. Fungi also use antagonism to reduce competition by producing antibodies, which suppress other microorganisms from growing. They produce many vitamins which promote plant growth. By competing with other fungus for nutrients, beneficial fungi prevent pathogenic and disease-causing organisms from getting established. 

Beneficial fungi along with some bacteria may also form protective webs and nets around roots and even leaves to protect the host plant (Lowenfels & Lewis, 2006; Sylvia et al., 2005). The fungus Trichoderma protects plant roots from attack by harmful microorganisms. Fungi also protect plants by supplying a protective covering to supply both water and phosphorus to the plant roots during droughts (Magdoff & Van Es, 2009). 

Relationship to Bacteria

Fungi generally reproduce asexually by spores (microscopic parts similar to plant seeds). Spore dispersal occurs in a variety of ways including triggers, jet propulsion, springs, and scents depending on the environment (Lowenfels & Lewis, 2006). Fungi spores may live 50 years in an inactive vegetative state as a spore. This allows the fungi to survive and remain viable by staying inactive until environmental conditions improve. 

Microbes spend most of their time hungry and looking for nutrient resources just to survive but fungus may remain viable for years. Most fungi survive by continual growth and translocation of nutrients in wide networks as they search for food or they survive through the production of resistant spores during times of stress (Lavelle & Spain, 2005). Natural soils tend to suppress germinating fungal spores, especially when nutrients are limiting (Sylvia et al., 2005).