What Are the Different Types of Arbuscular Mycorrhizae? A Complete Scientific Classification Guide
- Stanislav M.
- Feb 10
- 14 min read
Introduction
Arbuscular mycorrhizal fungi (AMF) represent one of the most important symbiotic relationships in terrestrial ecosystems, colonizing the roots of approximately 80% of vascular plant species worldwide. Understanding the diversity of arbuscular mycorrhizae is critical for agricultural professionals, plant scientists, and environmental researchers seeking to optimize plant growth, enhance soil health, and develop sustainable farming practices. This comprehensive guide explores the taxonomic classification, functional diversity, and ecological characteristics of different types of arbuscular mycorrhizal fungi, providing evidence-based information on the major families, genera, and species that define modern mycorrhizal science.
Phylum-Level Classification: Glomeromycota and Mucoromycota
Overview of Arbuscular Mycorrhizal Fungi Phylogeny
Arbuscular mycorrhizal fungi belong to the phylum Mucoromycota, specifically within the subphylum Glomeromycotina. This evolutionary lineage represents one of the oldest fungal groups, diverging from other major fungal phyla over 450 million years ago. The phylum Mucoromycota also includes the subphyla Mortierellomycotina and Mucoromycotina, with Glomeromycotina uniquely specialized for obligate symbiosis with plants.
Key Phylogenetic Distinctions:
Ancient lineage: Diverged before the evolution of Ascomycota and Basidiomycota (the more familiar fungi)
Obligate symbionts: Cannot survive or reproduce without a plant host, fundamentally distinguishing them from free-living fungi
Morphological simplicity: Lack fruiting bodies and spore-dispersal mechanisms of higher fungi
Universal associations: Form symbiotic partnerships across plant families, kingdoms, and ecological contexts
Order-Level Classification: Four Major Orders
The phylum Glomeromycota comprises four evolutionarily distinct orders, each with characteristic morphologies, ecological distributions, and functional capabilities:
1. Order Glomerales: The Dominant Agricultural AMF
Overview:The order Glomerales represents the most abundant and economically important arbuscular mycorrhizal fungi in agricultural systems worldwide, comprising the majority of species applied in commercial biofertilizer formulations.
Defining Characteristics:
Forms both arbuscules and vesicles (lipid storage structures)
Produces spores with distinctive chitinous spore walls
Exhibits high host plant compatibility across crop species
Dominates in phosphorus-rich and nutrient-abundant soils
Family-Level Structure (Order Glomerales):
The order Glomerales includes two major families:
Family Glomeraceae
Genera Within Glomeraceae (Schüßler et al., 2001; modern taxonomy):
Glomus (Type genus)
Funneliformis (formerly classified within Glomus)
Rhizophagus (formerly classified as Glomus intraradices and G. irregulare)
Sclerocystis
Simiglomus (recently erected genus)
Septoglomus (recently erected genus)
Ecological Characteristics:
Highly competitive in agricultural soils
Efficient phosphorus mobilization from soil pools
Broad host range supporting diverse crops
Population density often 10-100 fold higher than other AMF families in cultivated soils
Key Species in Glomeraceae:
Species | Former Name | Agricultural Importance | Host Specificity |
|---|---|---|---|
Glomus indicum | Glomus indicum | High (cereal crops) | Broad |
Funneliformis mosseae | Glomus mosseae | Very High (vegetables, legumes) | Broad |
Rhizophagus irregularis | Glomus irregulare | Very High (universal applicability) | Broad |
Rhizophagus intraradices | Glomus intraradices | Very High (field crops) | Broad |
Rhizophagus vesiculiferus | Glomus vesiculiferum | Moderate (specialized crops) | Moderate |
Distinct Advantage of Rhizophagus:Rhizophagus irregularis represents one of the most versatile and widely applied AMF species in agriculture, demonstrating exceptional colonization capacity across diverse plant hosts and soil types. The species exhibits:
Rapid root colonization (7-14 days post-inoculation)
Extensive extraradical hyphal networks (extending >100 times root surface area)
High phosphorus transfer efficiency (accounting for 81.8% of total plant P uptake in low-P soils)
Stress tolerance mechanisms enhancing drought and salinity resilience
Rhizophagus intraradices vs. Rhizophagus irregularis:Modern molecular phylogenetics has clarified that these represent two distinct species, historically confused in literature:
R. intraradices (formerly Glomus intraradices, strain FL208): Moderate to high effectiveness
R. irregularis (formerly Glomus irregulare, DAOM197198): Superior effectiveness and consistency
Genetic differentiation: >10% sequence divergence in ribosomal DNA regions
Family Claroideoglomeraceae
Genera Within Claroideoglomeraceae:
Claroideoglomus (type genus)
Viscospora (recently erected genus)
Ecological Characteristics:
Produces distinctive spore morphologies with multiple spore wall layers
Exhibits preference for slightly acidic to neutral soils (pH 5.5-7.0)
Lower competitive dominance compared to Glomeraceae in agricultural systems
Greater abundance in natural grasslands and forest ecosystems
Functional Properties:
Moderate phosphorus transfer efficiency
Enhanced organic matter decomposition capabilities
Greater enzymatic activity against complex organic substrates
Improved tolerance to soil acidification
2. Order Diversisporales: Ecologically Specialized AMF
Overview:The order Diversisporales encompasses functionally and morphologically diverse arbuscular mycorrhizal fungi with ecological specialization in low-phosphorus environments and complex organic matter degradation.
Defining Characteristics:
Arbuscules typically formed intracellularly
Vesicles either absent or of limited occurrence
Spores with distinctive multilayered walls
Greater enzyme diversity for organic matter mobilization
Family Structure (Order Diversisporales):
The order comprises five families with distinct ecological roles:
Family Diversisporaceae
Genera:
Diversispora
Otospora
Redeckera
Ecological Functions:
Specializes in organic phosphorus mobilization
Elevated enzyme activity (phosphatases, proteases) for organic matter decomposition
Particularly effective in high-organic-matter soils (>3% organic carbon)
Important in forest floor and litter layer nutrient cycling
Family Acaulosporaceae
Genera:
Acaulospora
Kuklospora
Ecological Characteristics:
Forms large spores (30-100 μm diameter) visible to naked eye
Sparse vesicle formation or absence
Adapted to low-nutrient tropical soils
Important in tropical forest ecosystems
Agricultural Significance:
Moderate effectiveness in agricultural systems
Enhanced stress tolerance to drought and heavy metals
Better adaptation to acidic soils compared to Glomeraceae
Family Pacisporaceae
Genus:
Pacispora
Specialization:
Adapted to extremely low-nutrient (oligotrophic) environments
Endemic to specific geographical regions
Limited agricultural application due to specialized habitat requirements
Family Entrophosporaceae
Genus:
Entrophospora
Characteristics:
Produces spores within hyphal network (distinctive feature)
Exhibits tolerance to heavy metal contamination
Effective in bioremediation applications for polluted soils
Family Gigasporaceae
Genera:
Gigaspora
Racocetra
Scutellospora
Orbispora
Distinctive Features:
Forms bulbous auxiliary cells (enlarged hyphal structures)
Some species produce large, distinctive spores (100-500 μm)
Exhibits preference for tropical and subtropical soils
Reduced agricultural application due to slower colonization rates
3. Order Paraglomerales: Ancestral AMF with Limited Distribution
Overview:The order Paraglomerales represents an ancient lineage of arbuscular mycorrhizal fungi with limited geographical distribution and narrow host specificity.
Defining Characteristics:
Arbuscules present but variable in morphology
Vesicles typically absent (distinguishing feature)
Spore walls with distinctive sculptured ornamentation
Restricted geographical range (primarily tropical regions)
Family Paraglomeraceae:
Genus:
Paraglomus
Ecological Characteristics:
Forms associations with graminoid plants (grasses, sedges)
Exhibits limited host range
Low relative abundance in most ecosystems (<5% of AMF community)
Greater abundance in wetland and riparian ecosystems
Agricultural Application:
Minimal commercial application
Specialized role in grassland and rangeland ecosystems
Potential utility for native plant restoration projects
4. Order Archaeosporales: The Most Basal AMF Lineage
Overview:The order Archaeosporales represents the most basal (evolutionarily oldest) lineage within Glomeromycota, with characteristics resembling the early-diverging ancestors of all arbuscular mycorrhizal fungi.
Defining Characteristics:
Produces small, simple spores
Arbuscules and vesicles both present, though variable
Exhibits limited metabolic capabilities compared to derived orders
Restricted distribution to specific soil types and climatic regions
Family Archaeosporaceae:
Genera:
Archaeospora (type genus)
Intraspora
Family Ambisporaceae:
Genus:
Ambispora
Ecological Distribution:
Predominantly temperate grasslands and forest ecosystems
Greater abundance in acidic to slightly acidic soils (pH 5.5-6.5)
Typically <10% of AMF community in most habitats
Functional Characteristics:
Enhanced tolerance to soil acidification and heavy metal stress
Moderate phosphorus mobilization capability
Potential utility in ecological restoration of degraded soils
Family-Level Classification Summary Table
The following table synthesizes the major families of arbuscular mycorrhizal fungi with their distinctive characteristics:
Family | Order | Key Genera | Spore Characteristics | Ecological Preference | Agricultural Value |
|---|---|---|---|---|---|
Glomeraceae | Glomerales | Glomus, Funneliformis, Rhizophagus, Sclerocystis | Thin-walled, globose | Nutrient-rich soils; pH 6.5-8.0 | Very High |
Claroideoglomeraceae | Glomerales | Claroideoglomus, Viscospora | Multilayered walls; distinctive ornamentation | Slightly acidic soils; pH 5.5-7.0 | Moderate-High |
Diversisporaceae | Diversisporales | Diversispora, Otospora, Redeckera | Complex wall structure; multilayered | High-organic-matter soils | Moderate |
Acaulosporaceae | Diversisporales | Acaulospora, Kuklospora | Large spores; thick walls | Tropical, low-nutrient soils | Moderate |
Pacisporaceae | Diversisporales | Pacispora | Distinctive morphology | Extremely oligotrophic soils | Limited |
Entrophosporaceae | Diversisporales | Entrophospora | Spores within network | Contaminated/stressed soils | Bioremediation |
Gigasporaceae | Diversisporales | Gigaspora, Racocetra, Scutellospora | Large, distinctive spores | Tropical/subtropical soils | Limited-Moderate |
Paraglomeraceae | Paraglomerales | Paraglomus | Small, sculptured spores | Tropical wetlands; grasses | Limited |
Archaeosporaceae | Archaeosporales | Archaeospora, Intraspora | Simple spores; variable morphology | Temperate grasslands; pH 5.5-6.5 | Limited-Moderate |
Ambisporaceae | Archaeosporales | Ambispora | Simple, pale spores | Acidic soils; temperate regions | Bioremediation |
Genus-Level Diversity: Key Agricultural Genera
Genus Rhizophagus: High-Performance AMF
Distribution and Significance:Rhizophagus represents one of the most applied genera in agricultural biofertilizer formulations, encompassing species with exceptional colonization capacity and nutrient transfer efficiency.
Species within Rhizophagus:
1. Rhizophagus irregularis (formerly Glomus irregulare)
CFU viability: 1 × 10⁸ - 1 × 10⁹ CFU per gram product
Colonization speed: 7-14 days to effective root colonization
Phosphorus transfer: Up to 81.8% of total plant P uptake in low-P soils
Host range: Exceptionally broad; effective on cereals, legumes, vegetables, fruit crops
Stress tolerance: Enhanced drought, salinity, and heavy metal tolerance
Ecological habitat preference: Broad tolerance to diverse soil types (pH 5.5-8.5)
Hyphal network extension: Extends 100-200× root surface area
2. Rhizophagus intraradices (formerly Glomus intraradices)
CFU viability: 1 × 10⁸ - 1 × 10⁹ CFU per gram product
Colonization speed: 10-21 days to effective colonization
Phosphorus transfer: 50-75% of total plant P uptake in low-P conditions
Host range: Broad; particularly effective on legumes and grasses
Stress tolerance: Moderate to good; moderate drought/salinity enhancement
Soil preference: Neutral to slightly alkaline soils (pH 6.5-7.8)
3. Rhizophagus vesiculiferus (formerly Glomus versiforme)
Relative abundance in field populations: 1-3% (minor component)
Specialization: Improved drought tolerance mechanisms
Host specificity: Moderate; some host preference evident
Persistence: Extended viability in storage
Genus Funneliformis: Broad-Spectrum Agricultural Effectiveness
Species within Funneliformis:
1. Funneliformis mosseae (formerly Glomus mosseae) -
Spore morphology: Globose to subglobose spores (70-150 μm diameter)
Active spore count: 245+ active spores per gram product
Colonization characteristics: Rapid root penetration; intracellular arbuscule formation
Nutrient mobilization: Exceptional phosphorus solubilization via organic acid secretion
Host compatibility: Universal; colonizes >80% of vascular plants
Agricultural application: Particularly effective on vegetables, legumes, pulses
Environmental tolerance: Moderate salinity and drought tolerance
Soil pH preference: Optimal 6.5-7.5; functional range 5.5-8.0
Field Performance:F. mosseae demonstrates consistent efficacy across diverse agronomic systems:
Wheat yield increase: 15-25%
Vegetable crop yield increase: 25-40%
Phosphorus uptake enhancement: 50-150%
Drought tolerance improvement: 20-35%
Genus Glomus: Traditional Commercial AMF
Species Diversity:Glomus remains the largest genus within Glomeraceae, encompassing numerous species with distinct ecological niches:
1. Glomus indicum
Relative field abundance: 0.6-1.2% of AMF community
Ecological preference: Tropical and subtropical soils
Host range: Moderate specificity; preference for legumes and grasses
Nutrient transfer: Moderate P mobilization; enhanced N uptake
Agricultural application: Regional importance in Asian agriculture
2. Glomus iranicum
Habitat: Arid and semi-arid soils
Distinctive adaptation: Extreme drought tolerance
Host specificity: Moderate; preference for arid-adapted plants
Field application: Minimal in conventional agriculture; specialized use in arid regions
Genus Claroideoglomus: Soil Structure Enhancement
Key Species:
1. Claroideoglomus lamellosum (formerly Glomus lamellosum)
Spore morphology: Distinctive multilayered wall structure
Unique capability: Enhanced soil aggregate stabilization
Glomalin production: Higher glomalin output compared to other AMF families
Soil structure benefit: Improved water-holding capacity and aggregate stability
Agricultural application: Valuable for soil remediation and carbon sequestration projects
Ecological Specialization:C. lamellosum exhibits superior performance in:
Degraded soils requiring structural rehabilitation
Carbon sequestration and climate mitigation applications
Sustainable agriculture transitions from chemical-intensive systems
Soil conservation in erosion-prone landscapes
Functional Classification: AMF Types Based on Plant Benefits
Beyond traditional taxonomic classification, arbuscular mycorrhizal fungi can be classified functionally based on the primary benefits provided to plant hosts:
Type 1: Phosphorus-Mobilizing AMF (High P-Transfer Phenotype)
Characteristics:
Exceptional phosphorus uptake and transfer capacity (>75% of plant P uptake)
High-affinity phosphate transporters (family Pht2)
Efficient organic phosphorus mineralization via phosphatase enzymes
Dominance in phosphorus-limited environments
Representative Species:
Rhizophagus irregularis
Funneliformis mosseae
Rhizophagus intraradices
Agricultural Application:
Phosphorus-deficient soils requiring amendment
Organic farming systems (chemical phosphate fertilizers prohibited)
Tropical soils with high P-fixation capacity
Cost reduction through decreased P fertilizer requirement
Type 2: Stress-Tolerance AMF (Drought & Salinity Phenotype)
Characteristics:
Enhanced water-uptake mechanisms via aquaporin proteins
Osmolyte production improving plant osmotic adjustment
Greater hyphal contribution to water transport (vs. nutrient transport)
Glomalin-mediated soil water-retention improvement
Representative Species:
Rhizophagus irregularis
Claroideoglomus lamellosum
Glomus iranicum
Functional Mechanisms:
Increased root hydraulic conductivity (10-20% improvement)
Improved soil water availability (15-25% increase in plant-accessible water)
Enhanced antioxidant enzyme activity reducing drought-induced oxidative stress
Agricultural Application:
Arid and semi-arid regions
Climate-change adaptation strategies
Irrigation-limited systems
Saline soil remediation
Type 3: Pathogen-Suppressive AMF (Biocontrol Phenotype)
Characteristics:
Enhanced production of antifungal metabolites
Competitive exclusion of soil-borne pathogens
Induced systemic resistance (ISR) priming of plant defenses
Altered root exudate chemistry unfavorable to pathogens
Representative Species:
Funneliformis mosseae
Rhizophagus irregularis
Acaulospora species
Disease Suppression Efficacy:
Root rot diseases (Pythium, Rhizoctonia): 60-80% severity reduction
Vascular wilts (Fusarium, Verticillium): 40-60% reduction
Root-knot nematodes: 30-50% population reduction
Type 4: Organic Matter-Degrading AMF (Saprotrophic Phenotype)
Characteristics:
Elevated enzymatic activity for organic compound breakdown
Efficient organic phosphorus and nitrogen mobilization
Enhanced litter decomposition contribution
Greater importance in high-organic-matter ecosystems
Representative Species:
Diversispora species
Claroideoglomus lamellosum
Acaulospora species
Ecological Niche:
Forest floor and litter-layer nutrition cycling
High-organic-matter agricultural soils (compost-amended systems)
Organic farming transitions
Natural grassland ecosystems
Species Composition in Natural and Agricultural Ecosystems
Field Study Example: AMF Community Structure (European Grassland)
A comprehensive molecular study examining AMF communities across phosphorus-treated and non-treated grassland sites identified:
Total AMF Diversity Recovered:
318 Amplicon Sequence Variants (ASVs) from Glomeromycota phylum
5 families identified: Glomeraceae, Claroideoglomeraceae, Diversisporaceae, Paraglomeraceae, Archaeosporaceae
20.7% of ASVs affiliated to genus level (primarily Rhizophagus, Funneliformis, Glomus)
12.2% of ASVs identified to species level
Dominant Species Identified:
Funneliformis mosseae - 10 ASVs; 12,591 reads (2.7% of total community)
Glomus indicum - 9 ASVs; 2,698 reads (0.6%)
Rhizophagus vesiculiferus - 6 ASVs; 8,033 reads (1.75%)
Core AMF Community:
26 ASVs constituted persistent "core" community across all sampling sites
25 core ASVs belonged to Glomeraceae family
Glomeraceae dominance: 40-60% of total AMF reads in field sites
Tropical and Subtropical AMF Diversity
Geographic Hotspot: Arabian Peninsula
A comprehensive survey documented:
20 genera and 61 species of Glomeromycota
Represents 46.51% of all known AMF genera globally
Represents 17.88% of all known AMF species globally
Dominant Families in Arid Regions:
Glomeraceae - 60-70% species representation
Diversisporaceae - 15-20%
Acaulosporaceae - 10-15%
Habitat Specialization in Tropical Systems:
Forest ecosystems: Diversisporaceae, Gigasporaceae dominance
Agricultural systems: Glomeraceae, Claroideoglomeraceae dominance
Wetland ecosystems: Paraglomeraceae, Archaeosporaceae enrichment
Structural Characteristics: Arbuscule Morphologies
Type 1: Paris-Type Arbuscule Morphology
Structural Characteristics:
Hyphae extend from cell to cell (intercellular spread pattern)
Continuous hyphal connections through multiple cortical layers
More efficient for rapid nutrient transport across root cortex
Typical of: Rhizophagus, Funneliformis, Glomus species
Functional Advantage:
Enhanced nutrient mobility through root tissues
Rapid phosphorus translocation to vascular tissues
Greater suitability for high-nutrient-demand crops (cereals, vegetables)
Type 2: Arum-Type Arbuscule Morphology
Structural Characteristics:
Hyphae remain within single cell (intracellular confinement)
Hyphal branching occurs within host cell vacuole
Creates dense nutrient-exchange interface within single cell
Typical of: Acaulospora, Gigaspora, Scutellospora species
Functional Advantage:
Compartmentalization may enhance selective nutrient transfer
Potential for greater control of nutrient exchange
Better adaptation to nutrient-poor tropical soils
Vesicle Formation and Function
Vesicle Presence vs. Absence
Vesicle-Forming AMF:
Families: Glomeraceae, Claroideoglomeraceae, Acaulosporaceae, Archaeosporaceae, Ambisporaceae
Function: Lipid and carbohydrate storage; intraradical energy reserves
Indicator of symbiotic maturity: Vesicle presence correlates with stable long-term colonization
Vesicle-Absent or Vesicle-Sparse AMF:
Families: Diversisporaceae, Gigasporaceae, Paraglomeraceae (partially)
Alternative structures: Auxiliary cells (bulbous hyphal structures) in Gigasporaceae
Functional significance: Greater metabolic flexibility; potential for broader ecological distribution
Spore Morphology and Identification
Spore Size Classification
Small Spores (<50 μm diameter):
Genera: Archaeospora, Paraglomus, Septoglomus
Characteristics: Rapid dissemination; ubiquitous distribution
Ecological preference: Often pioneer colonizers in disturbed soils
Medium Spores (50-150 μm diameter):
Genera: Glomus, Funneliformis, Rhizophagus, Claroideoglomus
Characteristics: Balanced spore production and vigor
Ecological preference: Dominant in most agricultural systems
Large Spores (>150 μm diameter):
Genera: Acaulospora, Gigaspora, Scutellospora
Characteristics: Sustained energy reserves; suited to variable environments
Ecological preference: More common in tropical and forest ecosystems
Spore Wall Structure Diversity
Single-Wall Spores:
Simple structure; thin spore wall
Characteristics: Limited stress tolerance; early-diverging lineages
Example: Archaeospora
Multi-Wall Spores:
Complex layered structure; multiple wall components
Characteristics: Enhanced durability; long-term soil persistence
Example: Acaulospora, Claroideoglomus, Diversispora
Ornamented Spores:
Distinctive surface sculpturing; ridges, tubercles, or mesh patterns
Function: May enhance adhesion to soil particles; protective function unclear
Example: Paraglomus, Scutellospora
Ecological Niche Differentiation
Soil pH Preference Gradient
AMF Family/Genus | Acidic Soils (pH <5.5) | Neutral Soils (pH 6.5-7.5) | Alkaline Soils (pH >8.0) |
|---|---|---|---|
Glomeraceae | Moderate | Excellent | Good |
Claroideoglomeraceae | Excellent | Good | Moderate |
Archaeosporaceae | Good | Moderate | Poor |
Diversisporaceae | Good | Good | Moderate |
Acaulosporaceae | Moderate | Moderate | Good (tropical species) |
Organic Matter Preference
Low Organic Matter Preference (<1% soil C):
Glomeraceae (nutrient-scavenging specialists)
Archaeosporaceae (oligotrophic adaptation)
High Organic Matter Preference (>2% soil C):
Diversisporaceae (organic matter degraders)
Acaulosporaceae (tropical forest specialists)
Gigasporaceae (complex organic substrate utilizers)
Commercial AMF Inoculant Formulations: Product Diversity
Single-Species Formulations
Advantages:
Standardized functionality
Predictable performance
Species-specific optimization possible
Limitations:
Lower ecological resilience
Potential monoculture disadvantages
Limited environmental buffering
Examples:
Funneliformis mosseae mono-inoculants
Rhizophagus irregularis mono-inoculants
Multi-Species Formulations
Advantages:
Enhanced ecosystem stability
Complementary nutrient-mobilization pathways
Redundancy in stress-tolerance functions
Broader host-plant compatibility
Common Consortia:
Rhizophagus irregularis + Funneliformis mosseae + Claroideoglomus etunicatum
Provides phosphorus mobilization (Rhizophagus), general vigor enhancement (Funneliformis), and stress tolerance (Claroideoglomus)
Proven Effective Multi-Species Combinations:According to Indo Gulf BioAg product recommendations:
Premium formulations contain Rhizophagus irregularis, Funneliformis mosseae, and Claroideoglomus etunicatum
Ensures compatibility across different plant types and soil conditions
Provides complementary functional traits for optimized plant growth
Symbiotic Efficiency and Performance Variation
Symbiotic Effectiveness Spectrum
Research demonstrates substantial variation in symbiotic effectiveness among AMF species and strains:
Highly Effective Symbionts:
Rhizophagus irregularis: Provides substantial P transfer (50-80% of plant acquisition); strong growth promotion
Funneliformis mosseae: Reliable performance across crop types; consistent phosphorus benefit
Moderate Effectiveness:
Rhizophagus intraradices: Good but slightly lower transfer efficiency than R. irregularis
Acaulospora species: Context-dependent; excellent in specific soil/plant combinations
Poor Symbionts (Low Effectiveness):
Some strains provide minimal P transfer while consuming substantial plant photosynthates
Examples: Certain Gigaspora and Scutellospora strains in agricultural systems
Critical Principle:Species identity and strain selection matter substantially. Within-species variation (strain differences) can exceed between-species variation, emphasizing importance of proven agricultural strains.
Functional Diversity: Nutrient Acquisition Specialization
Phosphorus-Acquisition Specialization
Inorganic P Specialists:
Glomeraceae (particularly Rhizophagus, Funneliformis, Glomus)
Efficient at extracting phosphate from soil solution
Dominant in nutrient-rich agricultural soils
Organic P Specialists:
Diversisporaceae (enhanced phosphatase activity)
Claroideoglomeraceae (elevated enzyme production)
Superior in high-organic-matter soils
Nitrogen-Acquisition Mechanisms
Ammonium (NH₄⁺) Uptake:
Most AMF families express ammonium transporters
Rhizophagus species show particularly high ammonium-transfer rates
Nitrate (NO₃⁻) Uptake:
Lower priority than phosphorus acquisition
Some families (Diversisporaceae) exhibit greater nitrate-uptake capability
Potential complementarity with legume-nodule nitrogen fixation
Organic Nitrogen:
Enhanced capability in Diversisporaceae (protease activity)
Important in organic farming systems with limited inorganic N
Emerging Taxonomy: Recent Reclassifications and Nomenclature
Taxonomic Changes in Recent Years
The arbuscular mycorrhizal fungi have undergone substantial nomenclatural revision due to molecular phylogenetics:
Major Reclassifications:
Glomus to Rhizophagus Transfers:
Glomus intraradices → Rhizophagus intraradices
Glomus irregulare → Rhizophagus irregularis
Glomus versiforme → Rhizophagus vesiculiferus
Glomus to Funneliformis Transfers:
Glomus mosseae → Funneliformis mosseae
Glomus caledonium → Funneliformis caledonium
Glomus Subgenus Elevation:
Erection of Simiglomus and Septoglomus as distinct genera within Glomeraceae
Reasons for Reclassification:
Molecular phylogenetics (ribosomal DNA, elongation factor sequences) revealed non-monophyly of original Glomus
Spore morphology re-evaluation showed species previously classified as Glomus belonged to distinct evolutionary lineages
Modern taxonomy emphasizes evolutionary relationships over morphological convenience
Conclusion
The diversity of arbuscular mycorrhizal fungi extends far beyond simple categorization, encompassing at least 4 orders, 10+ families, and 30+ commercial genera with hundreds of species exhibiting distinct ecological niches and functional specializations. Understanding this taxonomic and functional diversity enables agricultural professionals to select optimized inoculant formulations matching specific crop requirements, soil conditions, and management objectives.
The order Glomerales—particularly families Glomeraceae and Claroideoglomeraceae—dominates agricultural systems globally, with genera Rhizophagus, Funneliformis, Glomus, and Claroideoglomus representing the highest-performing agricultural AMF. Contemporary evidence strongly supports multi-species formulations containing Rhizophagus irregularis, Funneliformis mosseae, and Claroideoglomus etunicatum as optimal for diverse agricultural applications, providing complementary phosphorus mobilization, growth promotion, and stress-tolerance mechanisms.
For practitioners seeking to optimize arbuscular mycorrhizal fungal applications in agriculture, understanding species-specific characteristics, functional properties, and soil/climate compatibility represents the foundation for achieving maximum productivity gains and sustainable soil health improvement across diverse farming systems.
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