Key Differences Between Ectomycorrhizal and Arbuscular Mycorrhizal Fungi

Stanislav M.
Nov 5
4 min read

Photo credit: https://www.indefenseofplants.com/blog/2017/2/1/on-fungi-and-forest-diversity

Ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) fungi represent two fundamentally different symbiotic strategies for associating with plant roots, each with distinct structural features, ecological distributions, and functional outcomes.

Structural Architecture

The most fundamental difference lies in how fungal hyphae interact with root cells: pmc.ncbi.nlm.nih+4

Ectomycorrhizal Fungi

ECM fungi remain entirely external to root cells, forming two distinctive structures. The mantle or sheath is a dense hyphal covering surrounding the root surface, typically 10-40 micrometers thick, with hyphae extending several centimeters into surrounding soil. Within the root cortex, ECM fungi establish intercellular interfaces called the Hartig net—a latticework of highly branched hyphae occupying spaces between epidermal and cortical cells without penetrating cell walls. This arrangement provides an extensive contact surface for nutrient exchange while maintaining a physical barrier between fungal and plant cells.wikipedia+2

Arbuscular Mycorrhizal Fungi

AM fungi penetrate root cell walls and establish intracellular contacts, forming specialized structures called arbuscules—highly branched, tree-like hyphal projections that push into the plant cell membrane without breaking it. The fungus also forms vesicles, globular storage structures accumulating lipids and carbohydrates within or between cells. This intimate cellular penetration allows direct nutrient transfer across plant cell membranes.wikipedia+2

Fungal Taxonomy

The fungal partners differ significantly in evolutionary origin:zahradnictvolimbach+2

ECM fungi primarily belong to Basidiomycota and Ascomycota phyla, including familiar fruiting bodies like mushrooms, boletes, truffles, and the notorious death cap (Amanita species)biologydiscussion+2
AM fungi belong to the phylum Mucoromycota, specifically the subphylum Glomeromycotina, representing a more ancient fungal lineage than the ECM partnerswikipedia

Host Plant Specificity

The plant hosts associated with each mycorrhizal type are largely distinct:geeksforgeeks+3

Ectomycorrhizal associations form with approximately 2% of plant species, predominantly woody perennials including conifers (pine, spruce, fir, cedar), hardwoods (oak, beech, birch), and species in the dipterocarp, myrtle, willow, and rose families. ECM is particularly important in temperate and boreal forests.pmc.ncbi.nlm.nih+1

Arbuscular mycorrhizal associations are far more prevalent, occurring in approximately 80% of vascular plant families and in diverse habitats globally. AM occurs in agricultural crops (maize, wheat, soybeans), grasses, legumes, and both herbaceous and woody species across tropical and temperate ecosystems. AM fungi are considered the most prevalent plant symbiosis known.pmc.ncbi.nlm.nih+2

Nutrient Acquisition Strategies

Both mycorrhizal types enhance plant nutrition but through different mechanisms and nutrient profiles:mdpi+3

ECM Fungi

Excel at mobilizing nitrogen (N) and phosphorus (P) from organic substrates through secreted extracellular enzymes
Break down complex organic matter like leaf litter and humus, accessing nutrients locked in recalcitrant compounds
Show enhanced enzyme production for decomposition, supporting nutrient cycling in nutrient-poor forest soils
Particularly effective in low-nutrient environments, enabling tree survival in degraded soilspmc.ncbi.nlm.nih+2
ECM plants exhibit higher reliance on mycorrhizal fungi for nitrogen, as indicated by isotope tracer studies showing isotopically light nitrogen transferfrontiersin

AM Fungi

Specialize in capturing inorganic nutrients directly from soil solution, particularly phosphorus
Improve uptake of sulfur, nitrogen, and micronutrients (copper, zinc) through enhanced transporter expressionpmc.ncbi.nlm.nih
Most effective in nutrient-rich agricultural and grassland soils where soluble nutrients are readily available
Respond strongly to nitrogen deposition and show heightened sensitivity to nutrient availability changesmdpi+1
Produce glomalin, a glue-like protein that improves soil structure and water retentionpmc.ncbi.nlm.nih

Nutritional Exchange

The carbon compensation mechanisms differ between the two types:geeksforgeeks+1

AM fungi take up fatty acids and sugars from the plant host, with recent evidence showing that plant-derived fatty acids partially constitute the fungal lipid reserves in spores and vesicles.pmc.ncbi.nlm.nih

ECM fungi primarily receive carbohydrates and may have different metabolic requirements, though detailed mechanisms remain less well-characterized.pmc.ncbi.nlm.nih

Soil Function and Ecosystem Effects

These mycorrhizal types generate different soil and ecosystem outcomes:academic.oup+3

ECM fungi produce mycelium with higher concentrations of recalcitrant (resistant) chemical components, resulting in slower decomposition and greater carbon sequestration in forest soils. This contributes to the long-term carbon storage characteristic of temperate and boreal forests.nature

AM fungi produce mycelium with higher acid-hydrolysable components, enabling more rapid decomposition and nutrient cycling, supporting productivity in grasslands and agricultural systems.nature+1

Soil aggregation: AM fungi enhance soil particle aggregation through glomalin production, improving soil structure and water-holding capacity more effectively than ECM, particularly in response to nitrogen addition.mdpi

Ecological Dominance and Distribution

In temperate and boreal forests, ECM fungi dominate woody plant communities and drive nutrient cycling patterns. In tropical regions and agricultural systems, AM fungi are predominant. In subtropical forests, both types co-occur in complex communities with competitive or complementary interactions.pmc.ncbi.nlm.nih+2

Disease Resistance

Both mycorrhizal types enhance plant defense, but through different mechanisms:

AM fungi more commonly induce systemic acquired resistance (SAR) and induced systemic resistance (ISR), preparing plants for faster, stronger responses to pathogen attack. This priming effect protects against both soil-borne and foliar pathogens through plant-wide signaling.pmc.ncbi.nlm.nih

ECM fungi provide disease protection primarily through improved nutrition and physical barriers at the root surface, with systemic effects less commonly documented.pmc.ncbi.nlm.nih

Practical Applications

ECM importance: Critical for sustainable forestry and afforestation programs, where appropriate ECM inoculation of seedlings ensures successful establishment in nutrient-poor soils.biologydiscussion+1

AM importance: Valuable for agriculture and horticulture, with demonstrated yield benefits in crops like potatoes and increasing recognition for stress tolerance under drought and salinity.mdpi+1

Summary Comparison Table

Feature	Ectomycorrhizal (ECM)	Arbuscular Mycorrhizal (AM)
Hyphal penetration	External only (Hartig net, mantle)	Penetrates cell walls (arbuscules, vesicles)
Fungal phyla	Basidiomycota, Ascomycota	Glomeromycota (Mucoromycota)
Host plants	~2% of species (forest trees)	~80% of vascular families (crops, grasses, herbs)
Nutrient source	Organic compounds (humus, litter)	Inorganic soil solutions
Key nutrients mobilized	N, P from organic matter	P, S, micronutrients
Mycelium chemistry	Recalcitrant (slow decomposition)	Labile (fast cycling)
Soil aggregation	Moderate	Strong
Ecosystem dominance	Temperate/boreal forests	Tropical/agricultural systems
Carbon sequestration	High (slow mycelium decomposition)	Moderate
Disease resistance	Nutritional & physical	Systemic priming (SAR/ISR)

Both mycorrhizal types represent sophisticated evolutionary solutions to nutrient acquisition, with each excelling in different ecological contexts and supporting fundamentally different ecosystem functions.pmc.ncbi.nlm.nih+2