Fact Sheet FS1384
Mycorrhizal fungi are vital organisms that are essential to the health and function of terrestrial ecosystems. They originated more than 400 million years ago and strongly influenced the evolution and diversification of plants on Earth. Mycorrhizal fungi form symbiotic relationships with the roots of most land plants, benefiting both the fungi and the plants in a mutual exchange of resources. This ancient connection also involves other soil microbes, like bacteria, as well as being a fundamental driver of soil health and function.
Mycorrhizal fungi colonize plant roots and extend their thread-like hyphae into the surrounding soil, increasing the effective surface area for resource uptake. This growth forms an extensive mycelial network that explores soil volumes far beyond the reach of the plant's root system. As a result, the network greatly enhances the plant's ability to absorb water and essential nutrients. In return, the plant supplies the fungi with carbohydrates produced through photosynthesis (Figure 1).
Figure 1: Schematic representation of the mycorrhizal relationships in an Appalachian (hemlock)-northern hardwood forest, among mycorrhizal fungi and plant roots. The mycorrhizal fungi depicted here include an ectomycorrhizal species with a conspicuous fruiting body, the false death cap mushroom (Amanita citrina). Illustration credit: Jean Epiphan (c).
The Mycorrhizal Symbiosis: Benefits to Plants and Fungi
The relationship between plants and mycorrhizal fungi is usually of mutual benefit, with both parties gaining significant advantages.
Benefits for Plants
Benefits for Fungi
Types of Mycorrhizal Fungi
There are two primary types of mycorrhizal fungi, ectomycorrhizal and endomycorrhizal.
Ectomycorrhizal Fungi (EMF)
Ectomycorrhizal fungi (EMF) form a sheath around the root, creating a network of hyphae between the root cells without penetrating the cells. This structure is called the Hartig net and facilitates nutrient exchange at the root surface. EMF form associations mainly with woody plants like conifers, oaks (Quercus spp.), hickories (Carya spp.), and birches (Betula spp.) and are especially important in acidophilic forest ecosystems, where they facilitate the uptake of nitrogen and protect plants from soil pathogens. Some species of EMF mycorrhizal fungi have conspicuous fruiting bodies or mushrooms such as the poisonous fly agaric (Amanita muscaria) and edible and prized morels (Morchella spp.) and chanterelles (Chanterellus spp.).
Endomycorrhizal Fungi
Endomycorrhizal fungi colonize the inside of the plant's root cells. The most common type of endomycorrhizal fungi is called arbuscular mycorrhizal fungi (AMF), which form associations with approximately 80% of all plant species, including trees, shrubs, herbaceous plants and agricultural crops. AMF penetrate the root cells of plants, creating specialized structures called arbuscules. These are highly branched, tree-like structures that facilitate the exchange of nutrients and carbon between the plant and fungus. AMF are particularly adept at acquiring phosphorus, which is often a limiting nutrient in soils. AMF colonization is triggered best in low phosphorus soils; synthetic phosphorus fertilizer application prevents or hinders AMF colonization and function to benefit natural pathways for nutrient uptake.
Other main groups of endomycorrhizal fungi include Ericoid and Orchid.
Ericoid Mycorrhizal Fungi
Ericoid mycorrhizal fungi are specific to plants in the Ericaceae family, such as blueberries (Vaccinium spp.) and Rhododendron (Rhododendron spp.). This partnership allows ericaceous plants to thrive in boreal forests, bogs, heathlands, or tundra that have peaty, strongly acidic soils by mineralizing nitrogen, a limiting nutrient in these environments.
Orchid Mycorrhizal Fungi
Orchid mycorrhizal fungi are specific to the orchid family. Orchids will not germinate if an orchid mycorrhizal fungi connection is not present, requiring it for germination and healthy plant development.
There are two special groups of endomycorrhizal fungi that are found primarily in forests dominated by ectomycorrhizal-associated trees, such as oak, beech, and pine forests. These two groups are monotropoid and arbutoid.
Monotropoid Mycorrhizal Fungi
Monotropoid mycorrhizal fungi provide the connection between host plants like pines, oaks, and beech, and their obligate parasitic plants such as ghost pipe (Monotropa uniflora). These parasitic plants lack chlorophyll, do not photosynthesize, and instead obtain carbohydrates from their host plant through their mycorrhizal associations. Monotropoid associated plants are considered "friendly" parasites, as they do not cause harm to their host trees.
Arbutoid Mycorrhizal Fungi
Arbutoid mycorrhizal fungi are associated with specific groups of forest plants such as Pyrolas (Pyrola spp.), wintergreens (Chimaphila spp.), bearberries (Arcostaphylos spp.) and Arbutus (Arbutus spp.).
Sebacinoid Mycorrhizal Fungi
A unique group of mycorrhizal fungi, the Sebacinoids, can form differing mycorrhizal relationships including endomycorrhizal, ectomycorrhizal, ericoid, and orchid associations. They can have a wide range of interactions with many different plant partners.
Ectendomycorrhizal Mycorrhizal Fungi
A rare group of mycorrhizal fungi is Ectendomycorrhizal, which exhibit characteristics of ectomycorrhizal fungi, but penetrate cells like endomycorrhizal fungi. This ectendomycorrhizal association is found with some pines, spruce (Picea spp.) and larch (Larix spp.).
Vital Ecological and Environmental Roles of Mycorrhizal Fungi
Mycorrhizal fungi are indispensable to ecosystem health and functionality and crucial to plant health. They form networks that serve as communication and resource sharing pathways, especially in older forest systems where historic networks are intact (Figure 1). For example, trees under stress from pest or pathogen attack send chemical signals across the mycorrhizal network that trigger defenses in other susceptible trees. In addition, "mother" trees, the largest and oldest trees in the forest, are the most widely connected throughout the mycorrhizal network. They photosynthesize more than needed and send extra sugars to understory (shaded) seedlings to promote their growth and overall forest regeneration. Moreover, when a tree begins to slowly decline, it sends its resources through the mycorrhizal network to other connected plants to promote their health and success. As mycorrhizal fungi networks facilitate nutrient sharing and communication, they create more stable, resilient, and healthy plant communities. Mycorrhizal fungi networks can even suppress invasive plants by promoting native plant competition.
Environmental sustainability and landscape resilience are promoted by mycorrhizal fungi and their natural processes. Mycorrhizal fungi in the soil produce compounds like glomalin which help bind soil particles that greatly improve aggregation and soil structure. This process also helps to build or rebuild the structure of compacted soils, creating pore spaces that allow for water infiltration, water storage capacity, while reducing runoff and negative impacts from stormwater. Furthermore, mycorrhizal fungi play a large role in the global carbon cycle by stabilizing organic matter in the soil and storing carbon in their hyphal networks. The carbon storage performed by mycorrhizal fungi has been estimated at 13 gigatons annually, which is equivalent to 1/3rd of current, annual fossil fuel CO2 emissions. Overall, healthy soils with mycorrhizal fungi and healthy plant systems are inherently associated and depend on each other to maintain the health of our planet.
Applications in Agriculture, Horticulture, Silviculture, and Ecological Restoration
The benefits of mycorrhizal fungi have significant implications for anthropogenically created plant systems. In agriculture, crops inoculated with arbuscular mycorrhizal fungi show improved yields and overall stress resilience as well as noted pest and disease resistance (particularly with rhizosphere diseases), which reduces reliance on chemical pesticides. Promoting or inoculation with the right mycorrhizal fungi per crop type reduces or eliminates the need for chemical fertilizers by naturally enhancing nutrient availability. This is particularly important for phosphorus that is mined for fertilizers, as it is a non-renewable resource.
Mycorrhizal inoculation in nursery grown ornamental plants has shown significantly more robust growth, improved number of blooms, sped up flower timing, and decreased disease issues. For trees grown for silvicultural planting, inoculation with their obligate mycorrhizal fungi can be the difference between failure and survival.
When restoring degrading landscapes, reintroducing mycorrhizal fungi can accelerate soil recovery and improve plant establishment. Almost all native plants rely heavily on their fungal partners to thrive, making these fungi essential for restoring native plant communities. Furthermore, mycorrhizal fungi can be used as a tool to uptake heavy metals and toxins for ecological restoration in polluted soils.
Conclusion
Mycorrhizal fungi are a foundational aspect of terrestrial ecosystems, driving nutrient cycling, supporting plant health, and promoting biodiversity. Their ancient partnership with plants underscores their importance in the evolution and sustainability of life on Earth. Whether through protecting natural forest resilience, enhancing agricultural productivity, restoring degraded landscapes, or mitigating climate change, these remarkable fungi hold immense promise for a sustainable future. Recognizing and harnessing their potential is key to fostering resilient ecosystems and addressing the environmental challenges of the 21st century.
References
January 2026
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