Question

What are mycorrhizas and what is their significance?

Short answer

Mycorrhizas are symbiotic associations between fungi and plant roots that enhance nutrient uptake and contribute to plant health and soil fertility.

Step-by-step solution

Understanding Mycorrhizas

Mycorrhizas are symbiotic relationships between fungi and the roots of most terrestrial plants. In this association, the fungi colonize the root system of the host plant, enhancing its nutrient absorption capabilities.

Types of Mycorrhizas

There are primarily two types of mycorrhizae: ectomycorrhizas and endomycorrhizas (also known as arbuscular mycorrhizas or AM). Ectomycorrhizas form mainly with trees and create a dense fungal sheath around the roots, while endomycorrhizas penetrate the root cells forming arbuscules that facilitate nutrient exchange.

Role in Nutrient Exchange

Mycorrhizas play a crucial role in enhancing plant nutrient uptake. The fungi extend far into the soil, increasing the surface area available for absorbing water and nutrients, particularly phosphorus, nitrogen, and micronutrients, which are then transferred to the plant.

Environmental and Ecological Benefits

By improving plant nutrient uptake, mycorrhizas contribute to better plant growth and health. They also enhance soil structure and fertility, improve plant resistance to environmental stresses, and play a role in carbon cycling by decomposing organic matter.

Key concepts

Symbiotic Relationships

Mycorrhizas are fascinating examples of symbiotic relationships, which are essential for maintaining ecological balance. In symbiotic relationships, two different organisms live in close association, often supporting each other's survival. Mycorrhizas arise when fungi join with plant roots, each benefiting the other.
The plant supplies the fungi with carbohydrates formed during photosynthesis. In return, the fungi help the plant by enhancing its ability to absorb nutrients from the soil. This collaboration exemplifies mutualism, where both parties gain advantages.

• The plant gets increased access to nutrients and water.
• The fungi receive necessary sugars for survival.

By forming these partnerships, plants and fungi manage to thrive even in nutrient-poor environments, illustrating the power and significance of symbiotic relationships.

Plant Nutrient Absorption

A core benefit of mycorrhizal associations is the enhanced plant nutrient absorption. Nutrients like phosphorus and nitrogen are vital for plant health, but they can be challenging for roots to capture efficiently. Mycorrhizas help solve this problem.
The fungal networks extend far beyond the root's reach, tapping into deeper or less accessible soil layers to absorb nutrients.

• The fungi act as a conduit for nutrients, passing them from the soil to the plant.
• This increased access allows plants to grow larger, healthier, and more resilient.

Furthermore, mycorrhizas can aid in absorbing micronutrients like zinc and copper, which are important for various plant functions. In essence, these fungi maximize the nutrient uptake potential of plants, supporting their overall fitness and capacity to withstand environmental stresses.

Arbuscular Mycorrhizas

The arbuscular mycorrhizas (AM), also known as endomycorrhizas, are the most common type of mycorrhizal association. These fungi are known for entering the root cells of plants, where they form intricate structures called arbuscules.
Arbuscules act like tiny nutrient exchange sites within the root cells. They facilitate the transfer of essential nutrients from the fungi to the plant.

• Arbuscular mycorrhizas are prevalent across a broad range of plant species, including many agricultural crops.
• Their extensive network supports plant growth even in nutrient-poor soils.

This form of mycorrhiza is particularly beneficial for absorbing phosphorus, which is often limited in soils. By forming these specialized partnerships, arbuscular mycorrhizas play a crucial role in enhancing soil fertility and plant productivity.

Ectomycorrhizas

Ectomycorrhizas represent another major type of mycorrhizal association, primarily occurring with trees. Unlike arbuscular mycorrhizas, ectomycorrhizas do not penetrate root cells.
Instead, they envelop the root with a thick fungal sheath, known as the mantle, and form a network through the root's exterior cells called the Hartig net.

• This network aids significantly in the plant’s water and nutrient uptake.
• It is particularly beneficial for trees, helping them access nutrients in poor soil conditions.

By forming these networks, ectomycorrhizas help trees better withstand environmental stresses and contribute to the natural forest ecosystems' resilience and diversity. This type of mycorrhiza is especially well-suited for trees in temperate forests, where they play a pivotal role in nutrient cycling and supporting forest health and growth.