Rhizophagus irregularis is a widespread and ancient type of beneficial soil fungus. It belongs to the arbuscular mycorrhizal fungi (AMF) family, an ancient lineage dating back 400 to 450 million years, coinciding with the transition of plants from aquatic to terrestrial environments. It forms a widespread symbiotic association with approximately 65-80% of land plant species, including angiosperms, gymnosperms, and ferns. This fungus plays a significant role in promoting plant health and growth across diverse ecosystems.
Its Symbiotic Relationship with Plants
Rhizophagus irregularis establishes a mutualistic relationship with plants, known as arbuscular mycorrhizal symbiosis. The fungus colonizes host plant root cortex cells by forming hyphae, thread-like structures that grow between and into the cells. These hyphae then develop into highly branched arbuscules within the root cells, serving as primary sites for nutrient exchange.
Arbuscules are surrounded by a periarbuscular membrane, separating the fungal structure from the plant’s cytoplasm. These structures are ephemeral, typically lasting about a week before degrading. The fungus also forms vesicles, which act as storage sites and propagules, appearing within or between root cells.
The mutualistic exchange involves the fungus receiving carbohydrates and lipids from the plant, produced through photosynthesis, as its energy source. In return, the fungus extends its extensive hyphal network into the soil, significantly increasing the surface area for nutrient absorption. This network facilitates the uptake and transfer of essential mineral nutrients, such as inorganic phosphate and nitrogen, from the soil to the plant.
How It Boosts Plant Growth and Resilience
The fungus enhances nutrient absorption, particularly phosphorus and nitrogen, which are often limited in soil. It also improves the uptake of other micronutrients and potassium. This increased nutrient availability contributes to improved plant growth, overall health, and yield.
Beyond nutrient acquisition, Rhizophagus irregularis improves water absorption, leading to increased water content in plant shoots during drought recovery. This helps plants tolerate environmental stresses such as drought and salinity. The fungus also strengthens plants against other abiotic stresses, including heavy metal contamination and extreme temperatures.
The symbiotic relationship also increases plant resistance to certain soil-borne pathogens and improves overall plant resilience. For example, studies show that Rhizophagus irregularis boosts soybean growth by facilitating nitrogen fixation and enhances wheat’s phosphorus uptake, leading to improved grain yield and quality. This partnership results in healthier, more robust plants capable of thriving in less favorable conditions.
Broader Impact on Ecosystems and Agriculture
Rhizophagus irregularis has wide-ranging significance for natural ecosystems and agricultural practices. In natural environments, this fungus influences plant community dynamics by facilitating nutrient cycling and improving soil structure. Its hyphae and spores contribute to soil aggregation, which can mitigate soil erosion by surface water flow.
In agriculture, Rhizophagus irregularis offers potential for sustainable farming practices. By enhancing nutrient uptake and stress resistance, it can reduce reliance on synthetic fertilizers and pesticides, while improving crop yields.
Rhizophagus irregularis is recognized for its commercial applications as a biofertilizer or soil amendment. Inoculating crops with this fungus can lead to improved plant growth, fruit quality, and yield in various agriculturally relevant plants like maize and wheat. This approach aligns with efforts to restore degraded soils and promote more eco-friendly food production systems.