The key difference between root nodules and mycorrhizae is that root nodules are a type of symbiotic association between nitrogen-fixing bacteria and plant roots, while mycorrhizae are a type of symbiotic association between higher plant roots and fungi.
There are several types of symbiotic interactions between different organisms. Among them, mutualism, commensalism and parasitism are common. Root nodules and mycorrhizae are two different mutualistic interactions. Both partners are benefitted from the interaction. In root nodules, plant roots and nitrogen-fixing bacterium form symbiotic associations, while in mycorrhizae, plant roots and a fungus from the symbiotic association. Therefore, mycorrhizae are specific plant-fungus associations that benefit both the plant and fungal partners, while root nodules are specific plant-bacterium associations that give benefits to both plant and bacterial partners.
CONTENTS
1. Overview and Key Difference
2. What are Root Nodules
3. What are Mycorrhizae
4. Similarities Between Root Nodules and Mycorrhizae
5. Side by Side Comparison – Root Nodules vs Mycorrhizae in Tabular Form
6. Summary
What are Root Nodules?
Root nodules are symbiotic associations between plant roots and nitrogen-fixing bacteria. Leguminous plants primarily form root nodules. However, root nodules are present in non-leguminous plants as well. Nitrogen-fixing bacteria enter into root cells via root hairs and develop these specialized and well-organized organs called root nodules in the root system while inhabiting and replicating inside. They convert atmospheric nitrogen into ammonia. In legumes, nitrogen-fixing bacteria called Rhizobia live and fix nitrogen into ammonia in order to create amino acids and nucleotides in plants. In return, plants provide sugars to bacteria.
Figure 01: Root Nodules
Nodule formation is regulated by chemical signals between plants and microbes. Therefore, nodule formation starts with the leguminous bacterium receiving a signal from the host plant. Root nodules are agriculturally important structures. They reduce the requirement for nitrogen fertilizers in crops.
What are Mycorrhizae?
Mycorrhizae are a mutual symbiotic association between plant roots and fungi. The word ‘mycorrhiza’ refers to the fungus root. The fungus invades roots and forms a network of filaments in the root system. Fungus filaments draw nutrients from the soil into the root system. Therefore, the plant is able to access nutrients from a vast area of the soil. The major role of mycorrhizae is to enhance nutrient and water uptake by the host plant. Hence, mycorrhizae are very important in increasing plant nutrition and soil fertility. Fungus is also benefitted from the relationship. The green plant produces sugars or carbohydrates by photosynthesis and supplies them to the fungus. Therefore, both the fungus and plant get rewards from this interaction. Most importantly, plants are less susceptible to water stress when mycorrhizae are present. Not only that, fungi can store nutrients for plants. Moreover, fungi can break rocks and make essential nutrients such as potassium, calcium, zinc and magnesium available to plants. Furthermore, mycorrhizal fungi help the plant to resist infection by other fungi and bacteria. It is a type of mutually beneficial association. It is a non-disease-producing association.
Figure 02: Mycorrhizae
Mycorrhizae are seen in many plant roots. In fact, mycorrhizae are present in about 90% of all land plants. There are two types of mycorrhizae based on the way that fungus colonizes plant roots. They are endomycorrhizal fungi and ectomycorrhizal fungi. Endomycorrhizae colonizes intracellularly, penetrating the cell wall and invaginating the cell membrane. On the other hand, ectomycorrhizae colonize extracellularly without penetrating individual cells within the root. Arbuscular mycorrhizae are a type of endomycorrhizae, and they are the most commonly occurring in 85% of the plant species. Arbuscular mycorrhizae form either balloon-like (vesicles) or dichotomously branching invaginations when penetrating root cells. Ectomycorrhizae occur in 10% of plant species.
What are the Similarities Between Root Nodules and Mycorrhizae?
- Both root nodules and mycorrhizae are found in the root system of higher plants.
- Root nodules and mycorrhizae are two types of mutualistic interactions between two different organisms.
- In those symbiotic interactions, both partners benefit from the relationship.
- One partner is always a green plant in both types.
- However, these interactions are species or host-specific.
- They are agriculturally very important.
- These types of interactions increase soil fertility and crop productivity.
What is the Difference Between Root Nodules and Mycorrhizae?
Symbiotic associations between plant roots and nitrogen-fixing bacteria are called root nodules, while symbiotic associations between plant roots and fungi are called mycorrhizae. So, this is the key difference between root nodules and mycorrhizae. In root nodules, bacterium provides ammonia to plant in order to make amino acids and nucleotides, while in mycorrhizae, fungus enhances nutrient and water uptake of plant. This is another difference between root nodules and mycorrhizae.
The below infographic shows the differences between root nodules and mycorrhizal in tabular form.
Summary – Root Nodules vs Mycorrhizae
Root nodules and mycorrhizae are two-way relationships of sharing resources between two species. They are symbiotic mutualistic associations. They are found in plant roots. Root nodules are symbiotic associations between nitrogen-fixing bacteria and plant roots. Mycorrhizae are symbiotic associations between plant roots and fungi. Thus, this is the key difference between root nodules and mycorrhizae. Root nodules can be seen by our naked eye, while mycorrhizae are microscopic.
Reference:
1. “How It Works – Mycorrhizal Applications: Leaders in the Production of Mycorrhizal Fungi.” Mycorrhizal Applications | Leaders in the Production of Mycorrhizal Fungi, Available here.
2. Liu, Ailin, et al. “Interaction and Regulation of Carbon, Nitrogen, and Phosphorus Metabolisms in Root Nodules of Legumes.” Frontiers, Frontiers, 30 Nov. 2018, Available here.
Image Courtesy:
1. “Nitrogen fixation Fabaceae en” By Nefronus – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Mycorrhizal network” By Charlotte Roy, Salsero35, Nefronus – Adapted from this (CC BY-SA 4.0) via Commons Wikimedia
