Back to: Botany 200 Level
Hello, my brilliant student! I hope you’re having a fantastic day! Have you ever noticed how some plants grow so well even in poor soils, while others struggle? That’s because some plants form special partnerships with microorganisms that help them get the nutrients they need. These partnerships, known as symbiotic relationships, allow plants to absorb essential nutrients like nitrogen and phosphorus more efficiently. Today, we’ll learn about two of the most important plant-microbe relationships: nitrogen-fixing bacteria and mycorrhizae.
Symbiotic relationships (e.g., nitrogen-fixing bacteria and mycorrhizae)
A symbiotic relationship is a special kind of partnership where two organisms live closely together and help each other. In plants, these relationships often involve bacteria and fungi that help plants absorb nutrients in exchange for food or shelter.
1. Nitrogen-Fixing Bacteria and Plants
Nitrogen is one of the most important nutrients for plant growth, but even though 78% of the air is nitrogen gas (N₂), plants cannot use it directly. This is where nitrogen-fixing bacteria come in!
How It Works:
Certain bacteria, like Rhizobium, live inside the roots of leguminous plants (e.g., beans, peas, groundnuts, and soybeans).
These bacteria convert nitrogen gas (N₂) from the air into ammonium (NH₄⁺), which plants can use.
In return, the plant provides the bacteria with sugars and a safe place to live inside special root nodules.
Why Is This Important?
✔ Plants get ready-to-use nitrogen without needing chemical fertilisers.
✔ Improves soil fertility, benefiting other plants growing nearby.
✔ Reduces the need for synthetic nitrogen fertilisers, making farming more sustainable.
2. Mycorrhizae: Fungi and Plant Roots Working Together
Plants also struggle to absorb phosphorus, an essential nutrient for root development and energy transfer. That’s where mycorrhizal fungi help!
How It Works:
Mycorrhizae are special fungi that attach to plant roots and form a network of fine threads in the soil.
These fungal threads increase the plant’s root surface area, making it easier to absorb water and minerals, especially phosphorus (P).
In return, the plant feeds the fungi sugars produced during photosynthesis.
Types of Mycorrhizae:
Ectomycorrhizae – Form a sheath around root tips, common in trees like oak and pine.
Endomycorrhizae (Arbuscular Mycorrhizae) – Penetrate root cells, found in most crops and grasses.
Why Is This Important?
✔ Plants absorb more phosphorus and other minerals like calcium and magnesium.
✔ Increases plant drought resistance by improving water uptake.
✔ Protects roots from harmful diseases and soil toxins.
How Farmers Use These Relationships
Crop Rotation with Legumes – Farmers grow legumes (e.g., beans) before cereals (e.g., maize) to enrich the soil with nitrogen naturally.
Applying Mycorrhizal Inoculants – Some farmers add mycorrhizal fungi to the soil to help plants absorb nutrients better.
Avoiding Overuse of Chemical Fertilisers – Too much fertiliser can kill beneficial microbes, disrupting natural symbiotic relationships.
Summary
Symbiotic relationships help plants absorb essential nutrients.
Nitrogen-fixing bacteria (e.g., Rhizobium) convert atmospheric nitrogen into plant-usable forms.
Mycorrhizal fungi help plants absorb phosphorus and water.
These relationships improve soil fertility, reduce fertiliser use, and protect plant roots.
Farmers use crop rotation and mycorrhizal inoculants to take advantage of these partnerships.
Evaluation
- What is a symbiotic relationship in plants?
- How do Rhizobium bacteria help leguminous plants?
- What is the role of mycorrhizal fungi in plant nutrition?
- Give two examples of plants that benefit from mycorrhizal fungi.
- Why is crop rotation with legumes beneficial to farmers?
You’re doing amazing! Now you understand how plants and microbes work together to survive and grow better. Nature is truly fascinating, isn’t it? Keep going—Afrilearn is here to make learning fun and exciting! See you in the next lesson!
School Admin? Grow your school faster with Africa's most trusted school management softwareGet more class notes, videos, homework help, exam practice on Android [DOWNLOAD]
Get more class notes, videos, homework help, exam practice on iPhone [DOWNLOAD]