Q.23 Mycorrhizal fungi helps in delivery of which key ions to the plant system?
Mycorrhizal fungi primarily aid plants by enhancing the uptake of phosphate ions through their extensive hyphal networks, making option (1) the correct answer.
Option Analysis
Phosphate Ions (1) – Correct
Mycorrhizal fungi, especially arbuscular types, extend hyphae into soil to access immobile phosphate ions (PO₄³⁻) beyond root reach, solubilizing and delivering them to plants in exchange for carbohydrates. This boosts phosphorus nutrition, vital for ATP, DNA, and root growth, with studies showing up to 20% improved P uptake.
Sodium Ions (2) – Incorrect
Sodium ions (Na⁺) are not key targets; fungi may regulate Na⁺/K⁺ ratios under salinity stress but do not primarily deliver Na⁺, which plants often limit as a non-essential nutrient.
Chloride Ions (3) – Incorrect
Chloride ions (Cl⁻) move freely in soil solution via mass flow or diffusion; mycorrhizae provide no specialized delivery, as plants absorb them directly through roots.
Carbonate Ions (4) – Incorrect
Carbonate ions (CO₃²⁻) are rare in soil and not plant nutrients; fungi focus on macronutrients like P, not carbonates, which relate more to pH buffering.
Mycorrhizal fungi phosphate ions delivery is a critical symbiotic process where fungi boost plant phosphorus nutrition. This association powers over 80% of land plants, improving growth in nutrient-poor soils.
Symbiotic Mechanism
Mycorrhizal fungi form arbuscules in roots, extending hyphae to mine soil for phosphate ions, which diffuse slowly due to low mobility. Fungi release acids and enzymes to solubilize bound P, transferring it via transporters like PT (phosphate transporters) in exchange for 20% of plant-fixed carbon.
| Nutrient | Mycorrhizal Role | Plant Benefit |
|---|---|---|
| Phosphate (PO₄³⁻) | High uptake via hyphae | ATP synthesis, root development |
| Nitrogen (N) | Moderate cycling | Growth, chlorophyll |
| Micronutrients (Zn, Cu) | Enhanced access | Enzyme function |
| Sodium (Na⁺), Chloride (Cl⁻) | Minimal/none | Not primary targets |
Agricultural and Exam Relevance
In agriculture, inoculating crops with mycorrhizae cuts fertilizer needs by 25-50%, aiding sustainable farming amid P depletion. For exams like CUET PG Botany or GATE Life Sciences, remember phosphate ions as the hallmark, distinguishing from non-essential ions like sodium or chloride. This edge proves vital in phosphorus-limited Indian soils, like Rajasthan’s arid zones.
