Difference Between Mycorrhiza and Coralloid Roots

The key difference between mycorrhiza and coralloid roots is that mycorrhiza is a type of mutualistic association occurring between a higher plant and a fungus while coralloid roots are negatively geotropic roots of cycads which are in a mutualistic association with nitrogen-fixing cyanobacteria.

Symbiosis is a long term association between two different species of organisms that live together. There are three types of symbiotic relationships as parasitism, mutualism and commensalism. Mutualism is a type of symbiotic relationship in which both parties benefit from the relationship. Mycorrhiza and coralloid roots are two types of mutualistic interactions. Mycorrhiza is a mutualistic association between a fungus and roots of vascular plants. Coralloid roots are a special type of root system of cycads which house nitrogen-fixing cyanobacteria.

CONTENTS

1. Overview and Key Difference
2. What is Mycorrhiza
3. What are Coralloid Roots
4. Similarities Between Mycorrhiza and Coralloid Roots
5. Side by Side Comparison – Mycorrhiza vs Coralloid Roots in Tabular Form
6. Summary

What is Mycorrhiza?

Mycorrhiza is a type of symbiotic relationship that occurs between a fungus and the roots of a higher plant. It is a type of mutualistic association which is beneficial for both partners. In mycorrhiza, both plant and fungus reach benefits from their association. Fungal hyphae penetrate the soil and bring nutrients to the plant. The plant, in turn, assimilates carbohydrates and shares them with the fungus. Hence, it is an ecologically important relationship. Most importantly, when the plant roots do not have access to the nutrients, fungal hyphae can grow several meters and transport water and nutrients, especially nitrogen, phosphorus, potassium to the roots. Hence, nutrient deficiency symptoms are less likely to occur on plants which are in this symbiotic association. About 85% of vascular plants possess endomycorrhizal associations. In addition, fungus protects the plant from root pathogens. Therefore, mycorrhizae are very important associations in the ecosystems.

Difference Between Mycorrhiza and Coralloid Roots

Figure 01: Mycorrhiza

There are two types of mycorrhizae as ectomycorrhizae and endomycorrhizae. Ectomycorrhizae do not form arbuscules and vesicles. Also, their hyphae do not penetrate the cortical cells of the plant root. However, ectomycorrhizae are really important since they help plants to explore nutrients in the soil and protect plant roots from root pathogens. In endomycorrhizae, fungal hyphae penetrate the cortical cells of the plant roots and form vesicles and arbuscules. Endomycorrhizae are more common than ectomycorrhizae. Fungi from Ascomycota and Basidiomycota help in forming ectomycorrhizal association while fungi from Glomeromycota help in forming endomycorrhizae.

What are Coralloid Roots?

Coralloid roots are specialized symbiotic roots of cycads. Cycads form this mutualistic association with cyanobacteria or blue green algae. Therefore, coralloid roots are a special type of root system that houses symbiotic nitrogen-fixing cyanobacteria, especially Anabaena. These roots are negatively geotropic. Cycads are the only members of gymnosperms that are capable of forming this new association with cyanobionts. In this association, cyanobacteria fix nitrogen for their host plant cycad. Cyanobacteria fix atmospheric N₂into useful forms of nitrogen.

Key Difference - Mycorrhiza vs Coralloid Roots

Figure 02: Coralloid Roots

Coralloid roots grow beneath the soil surface. Hence, cyanobacteria cannot carry out photosynthesis. While staying inside the roots, cyanobacterium receives protection, stable environment and nutrients, especially carbon from the plant. The plant receives fixed nitrogen. Both plant (Cycas) and cyanobacterium (Anabaena) benefit from their mutualistic association. Anabaena cicadae or Nostoc cicadae are the two cyanobacteria identified commonly in coralloid roots of cycads.

What are the Similarities Between Mycorrhiza and Coralloid Roots?

Both mycorrhiza and coralloid roots are two types of symbiotic associations.
They are examples of mutualism.
In both associations, both partners are benefitted from the symbiosis.
One partner in both associations is a higher plant.

What is the Difference Between Mycorrhiza and Coralloid Roots?

Mycorrhiza is a symbiotic association between roots of a higher plant and a fungus. Coralloid roots are specialized cycads roots that are in symbiotic association with nitrogen-fixing cyanobacteria. So, this is the key difference between mycorrhiza and coralloid roots. Both mycorrhiza and coralloid roots are mutualistic interactions which benefit both partners in the association.

Below infographic tabulates the differences between mycorrhiza and coralloid roots for side by side comparison.

Summary – Mycorrhiza vs Coralloid Roots

Mycorrhiza is a symbiotic association between a fungus and a higher plant roots. Coralloid roots are another symbiotic association between cycads roots and cyanobacteria. Both associations are examples of mutualism, which is a type of symbiosis in which both partners are benefiting from their association. Thus, this is the summary of the difference between mycorrhiza and coralloid roots.

Reference:

1. “Coralloid Roots and Nitrogen Fixation.” The Cycad Pages, Available here.
2. French, Katherine E. “Engineering Mycorrhizal Symbioses to Alter Plant Metabolism and Improve Crop Health.” Frontiers, Frontiers, 11 July 2017, Available here.