Q.Mention the kind of interaction mycorrhizae exhibit. How is Glomus in mycorrhizal association beneficial to the plants ?
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Start your 14-day free trial to unlock the full solution →Mycorrhizae exhibit a mutualistic (symbiotic) interaction. The fungus Glomus (an arbuscular mycorrhizal fungus) benefits plants by enhancing phosphorus and mineral uptake, improving water absorption, and protecting roots from pathogens — in exchange for carbohydrates from the plant.
Concept and Intuition
Mycorrhizae are not a single organism but a symbiotic association between certain soil fungi and the roots of most vascular plants. The word itself comes from Greek: mykes (fungus) + rhiza (root). This is a classic example of mutualism — both partners gain something essential.
The fungus cannot photosynthesise, so it gets sugars and organic nutrients from the plant. In return, the fungal hyphae (thread-like filaments) extend far beyond the root's reach, acting like an extension of the root system. This dramatically increases the surface area for absorption, especially for immobile nutrients like phosphorus, which diffuse slowly in soil.
Glomus is a genus of fungi that forms arbuscular mycorrhizae (AM) — the most common type. Inside root cells, Glomus produces tree-like structures called arbuscules that are the main sites of nutrient exchange. This is not a parasitic relationship; the plant remains healthy and often grows better.
A common mistake is to think mycorrhizae are parasitic or that Glomus harms the plant. In fact, the interaction is obligate for the fungus (it cannot survive without a host) but facultative for most plants — though plants in poor soils depend heavily on it.
Step-by-step Explanation
1. Identify the type of interaction.
Mycorrhizae are a mutualistic symbiosis — both organisms benefit. The fungus gets carbohydrates (photosynthates) from the plant. The plant gets increased access to water and dissolved minerals, especially phosphorus, nitrogen, and micronutrients like zinc and copper. This is not competition, predation, or commensalism — it is a textbook mutualism.
2. Understand how Glomus specifically helps plants.
Glomus species are arbuscular mycorrhizal fungi (AMF). They penetrate the root cortex and form arbuscules inside cortical cells. The benefits are multiple:
- Enhanced phosphorus uptake: Phosphorus is often bound to soil particles and moves slowly. Fungal hyphae can explore a much larger volume of soil — up to 100 times more surface area than roots alone — and release phosphatases that solubilise organic phosphorus.
- Improved water relations: The hyphal network acts like a sponge, drawing water from soil pores that roots cannot reach. This helps plants tolerate drought. …
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