Mycorrhiza is the symbiotic relationship between fungi and plants. The name "mycorrhiza" describes the function of the fungus in the plant's root system or rhizosphere. Mycorrhizae are crucial to soil biology, chemistry, and plant nutrition. When two organisms form a mycorrhizal relationship, the fungus colonizes the host plant's root tissues either intracellularly, as in the case of arbuscular mycorrhizal fungi (AMF or AM), or extracellularly, as in the case of ectomycorrhizal fungi. Sometimes the association is mutualistic. Mycorrhizae may associate parasitically with host plants depending on the species or the situation. This article will explain to you about Mycorrhiza which will be helpful in preparing the Environment Syllabus for the UPSC Civil Service exam.

Mycorrhiza

What exactly is Mycorrhiza?

• The symbiotic association between fungi and plants forms mycorrhiza.
• A symbiotic relationship between a green plant and a fungus is known as a mycorrhiza.
• By using photosynthesis, the plant creates organic molecules like sugars and gives them to the fungus.
• Although mycorrhizas are found in the roots of vascular plants, bryophytes also have relationships resembling them, and there is fossil evidence that early land plants without roots formed arbuscular mycorrhizal associations.
• Despite some families, including Brassicaceae and Chenopodiaceae, being unable to create mycorrhizal connections, the majority of plant species can.
• The arbuscular form is the most prevalent and is found in 70% of plant species, including important agricultural plants like wheat and rice.

Mycorrhiza - Types

• The two types of mycorrhizas most commonly detected are ectomycorrhizas and endomycorrhizas.
• The ectomycorrhizal fungi's hyphae do not penetrate individual root cells, while endomycorrhizal fungi's hyphae penetrate the cell membrane and break down the cell wall.
• This distinguishes the two types.

Ectomycorrhiza

• In an ectomycorrhizal relationship, the fungus creates a sheath or mantle on top of the surface of the tiny lateral roots of the host trees and injects certain hyphae into the intercellular spaces of the outer cortex, where they congeal to form a structure known as a Hartignet.
• Vesicles and abuscules, which are often found in endomycorrhizae, are not present.
• The lateral roots that the fungal mantle covers frequently take on a swollen or coralloid shape.
• Pines and Mushrooms are an excellent example of this type.
• Ectomycorrhizal fungi play a crucial role in the process of reforestation.
• It is always made sure that the seedlings in developing pine forests are injected with soil having the proper strains of ectomycorrhizal fungus.
• Compared to non-mycorrhizal plants, trees with the ectomycorrhizal association are better able to develop in nutrient-deficient environments because of their increased capacity to absorb nutrients from the soil.

Endomycorrhiza

• The majority of higher plant species have endomycorrhizal relationships, which are more widespread than ecto-mycorrhizal ones.
• Orchid endo-mycorrhizae are among the most well-known. It is common knowledge that orchids require fungus to develop in their natural environment.
• Endomycorrhizal fungi infiltrate the root cells and are often confined to the cortical region, infrequently crossing the endodermis.
• Within the cells, the vesicular-arbuscular types create distinctive structures.
• These structures grow in the cells for a while before degenerating and eventually decomposing, feeding the host.
• Endomycorrhizal fungi are exclusively found in plant roots; they never infect the plant's leaves.
• Perhaps a preventive factor developed by the green parts keeps the fungi from intruding on the aerial parts.
• The absence of fungal development in the root beneath the aerial sections suggests this.

Ectomycorrhiza Vs Endomycorrhiza

Mycorrhiza - Mutualist Dynamics

• Most plant species' roots have a mutualistic interaction with mycorrhizal fungi.
• The term "mycorrhizal" refers to a relationship in which both the plants and the portions of their roots that host the fungi are present.
• Only a small number of mycorrhizal connections between different plant species and fungus have been studied thus far.
• However, 95% of the analysed plant families are predominately mycorrhizal, either in the sense that the majority of their species connect favourably with mycorrhizae or are wholly dependent on mycorrhizae.
• The Orchidaceae is well-known for being a family in which even germination of seeds is lethal in the absence of the proper mycorrhizae.

Benefits of Mycorrhizal Association

• The uptake of phosphorus and trace elements by plants can be increased via mycorrhizas.
• They accomplish this by increasing the amount of soil the plant explores.
• The hyphae of mycorrhizal fungi are extremely thin, measuring between 1 and 10 thousandths of a millimetre in width.
• These hyphae search the soil for nutrients, carry those nutrients back to the host plant, and aid in aggregating soil particles.
• Because phosphorus does not travel as readily in the soil solution as nitrogen does, this property of mycorrhizal fungus is particularly crucial for plant uptake.
• When there is a lack of phosphorus in the soil, plants with mycorrhizas on their root systems have better access to and may absorb more phosphorus than other plants.
• Plant roots must go into the soil to find trace metals like copper and zinc because they behave in the soil similarly to phosphorus.
• Additionally, mycorrhizal fungi can improve soil aggregation.
• The hyphae establish networks between roots of the same plant and between roots of different plants, as well as between roots of the same plant and soil particles (even different types of plants).
• Additionally, they create networks within the roots they colonise. The term "mycelium" is also used to describe these networks of hyphae.

Conclusion

All ecosystems on Earth, but especially those with significant mycorrhizal soil biota populations, depend heavily on temperature. The majority of ecosystems on Earth, notably those in the Arctic, have a large number of plants that depend on mycorrhizae to live. This makes fungi crucial to the survival of the planet. Understanding this fungus and its symbioses is currently an active field of scientific inquiry because of their significance to a healthy ecosystem.

GS Mains Questions and Model Answers

Q1: Explain the role of mycorrhizal associations in promoting plant health and nutrient uptake.

Answer: Mycorrhizal associations are symbiotic relationships between fungi and plant roots that enhance nutrient and water uptake. The fungi increase the root's surface area, allowing for more efficient absorption of essential nutrients like phosphorus, nitrogen, and micronutrients from the soil. Mycorrhizae also improve plant resistance to pathogens, increase tolerance to drought and stress, and promote overall plant health. This mutualistic relationship provides carbohydrates to the fungi while benefiting plant growth and productivity. Mycorrhizae are vital for sustainable agriculture, contributing to soil fertility and reducing the need for chemical fertilizers.

Q2: Discuss the types of mycorrhizae and their significance in plant-fungal interactions.

Answer: There are two main types of mycorrhizae: arbuscular mycorrhizae (AM) and ectomycorrhizae. Arbuscular mycorrhizae penetrate plant root cells and form structures called arbuscules that facilitate nutrient exchange. They are the most common type, found in many crops and grasses. Ectomycorrhizae, on the other hand, form a sheath around plant roots and interact with root cells externally. They are often associated with trees and forest plants. Both types enhance nutrient uptake, protect against pathogens, and contribute to soil health. These plant-fungal interactions are crucial for ecosystem stability and agricultural productivity.

Q3: Analyze the impact of mycorrhizae on soil health and their potential application in sustainable agriculture.

Answer: Mycorrhizae positively impact soil health by enhancing soil structure, aeration, and nutrient cycling. The fungal hyphae bind soil particles, creating a stable structure that improves water retention and aeration. Mycorrhizae also promote the decomposition of organic matter and facilitate nutrient availability, contributing to soil fertility. In sustainable agriculture, the introduction of mycorrhizal inoculants reduces the need for chemical fertilizers, improves crop yields, and enhances plant resilience to stress. By fostering healthier soils and reducing environmental impact, mycorrhizae play a key role in promoting sustainable farming practices and resilient ecosystems.

Previous Year Questions on  Mycorrhiza

1. UPSC CSE 2020

Question: Evaluate the role of mycorrhizae in enhancing plant productivity and resilience in agriculture.

Answer: Mycorrhizae play a critical role in enhancing plant productivity and resilience by improving nutrient uptake, particularly phosphorus and nitrogen, which are essential for plant growth. The symbiotic association increases the surface area of roots, allowing better absorption of water and minerals. Mycorrhizal fungi also offer protection against soil-borne pathogens, improve drought tolerance, and reduce the need for chemical fertilizers. In agriculture, mycorrhizal inoculants are used to promote sustainable crop production, improve soil health, and support plants in stress conditions, thus contributing to higher productivity and resilience in farming systems.

2. UPSC CSE 2019

Question: Discuss the ecological benefits of mycorrhizal associations in natural and agricultural ecosystems.

Answer: Mycorrhizal associations offer numerous ecological benefits in both natural and agricultural ecosystems. They enhance nutrient cycling and soil structure, improve plant health, and increase biodiversity. By forming symbiotic relationships with plants, mycorrhizae enable more efficient nutrient uptake, promote resilience to drought and disease, and reduce reliance on chemical fertilizers. In natural ecosystems, they contribute to forest health and regeneration, while in agriculture, they support sustainable practices and productivity. Mycorrhizae also help mitigate soil erosion by binding soil particles, making them integral to ecosystem stability and health.