When you look around in nature, you don’t see anyone with nutrient bottles or watering the forest, grass or trees. The reason is that the plant kingdom has established symbiotic relationships with the microbes and fungi present in the soil for millions of years.
In this article, we discuss what symbiotic relationships are, how plants benefit, the main types of microorganisms, how they convert food, how to inoculate your growing medium and much more.
What is a symbiotic micro-organism?
Symbiotic micro-organisms are living organisms, such as bacteria and fungi, that form a mutually beneficial relationship with plants. Unlike parasitism, where one organism harms the other, symbiosis allows both to thrive.
In plants, this association often occurs in the soil, where micro-organisms interact closely with roots. The micro-organisms help the plants access essential nutrients, while the plants provide them with energy in the form of carbohydrates produced during photosynthesis.
How do symbiotic microorganisms interact with plants?
Plants and micro-organisms form their association through root exudates. Plants release a mixture of sugars, amino acids and organic acids into the soil that attract beneficial microbes such as mycorrhizal fungi and nitrogen-fixing bacteria.
Once these microbes attach to the root hairs, a symbiotic exchange begins:
• Nutrient uptake:
o Mycorrhizal fungi spread their hyphae throughout the soil, increasing the root surface area and helping plants absorb hard-to-reach nutrients such as phosphorus and nitrogen.
Nitrogen-fixing bacteria, such as Rhizobium, convert atmospheric nitrogen into ammonium, a form that plants can use.
• Defence against pathogens:
o Some microbes form a barrier around roots, protecting them from harmful pathogens. Others produce antimicrobial compounds to suppress disease-causing organisms.
• Improved soil health:
o Microorganisms break down organic matter into simpler nutrients, enriching the soil and supporting a healthy ecosystem for future plant growth.
What are the benefits of growing plants with symbiotic micro-organisms?
1. Faster decomposition of organic matter
Research shows that micro-organisms can increase decomposition rates by up to 30%, releasing essential nutrients for plant uptake.
2. Nutrient supply through microbial activity
Microbes and fungi process nutrients from the soil and make them available to the plant, ensuring a constant supply. This dynamic exchange supports constant growth.
3. Conversion of nutrients for plant needs
Certain bacteria can convert nutrients into forms that plants can easily absorb. For example, nitrogen-fixing bacteria such as Rhizobium convert atmospheric nitrogen into ammonium, a form accessible to plants.
4. Trichoderma defence against pathogens
The Trichoderma fungus acts as a biological control agent, combating harmful pathogens. It is particularly effective against anaerobic pathogens, promoting healthier root systems.
5. Increased root mass and size
Symbiotic interactions can significantly increase root development. Mycorrhizal fungi, for example, expand the plant’s root network by up to 500%, improving access to water and nutrients.
Why are symbiotic micro-organisms important for agriculture?
Symbiotic micro-organisms play a key role in sustainable agriculture. Their natural processes reduce dependence on synthetic inputs and support long-term soil health.
• Sustainable nutrient cycling: Microorganisms improve nutrient availability, reducing the need for chemical fertilisers.
• Improved plant resilience: Plants with symbiotic microbes are more resistant to stresses such as drought, salinity and pests.
• Soil fertility: By keeping the soil food web in balance, micro-organisms help soils to be fertile and crops to yield more over time.
The 3 main types of symbiotic micro-organisms
There are three main types of symbiotic micro-organisms that interact with plants, each of which plays a unique role in plant health and soil balance:
1. Rhizobacteria: Root bacteria.
Rhizobacteria are beneficial bacteria that live in close association with plant roots. They contribute to plant health by fixing nitrogen, producing growth hormones and protecting plants from pathogens. The most common genera are:
– Azotobacter
– Pseudomonas
– Bacillus
– Rhizobium
– Serratia
– Burkholderia
2. Arbuscular mycorrhizal fungi (AMF)
AMF form a symbiotic relationship with most terrestrial plants. They help plants to absorb phosphorus, protect roots during drought and improve tolerance to heat stress. The key genera are:
– Glomus mosseae
– Glomus aggregatum
– Gigaspora margarita
AMF are especially crucial in nutrient-poor soils, where their extensive hyphal networks improve nutrient and water uptake.
3. Trichoderma: The gatekeepers
Trichoderma fungi are known for their aggressive colonisation of roots and soil, helping plants by:
– Breaking down organic matter to release nutrients.
– Competing with harmful microbes to maintain a beneficial microbial balance.
– Improving root growth and resistance to pathogens.
Common species used in agriculture include:
– Trichoderma harzianum
– Trichoderma asperellum
– Trichoderma viride
What about probiotic bacteria in soil?
Although not symbiotic, probiotic bacteria play a complementary role in soil ecosystems. They break down organic matter, releasing nutrients that feed plants and other microorganisms. Some key examples are:
– Bacillus subtilis
– Lactobacillus
– Bifidobacterium
– Saccharomyces
These bacteria contribute to the soil food web by breaking down complex organic compounds and promoting microbial diversity.
What do symbiotic microorganisms eat?
Symbiotic microorganisms rely on carbon-rich compounds provided by plants and organic matter, but what are these food sources, we tell you below:
• Root exudates
Plants secrete carbohydrates, amino acids and organic acids into the soil that feed beneficial microbes.
• Soil additives
o Molasses solutions provide simple sugars to the microbes, stimulating their activity.
o Biochar acts as a long-term carbon source, creating a habitat for the microbes.
o Fish or algae emulsions replenish nutrients and enhance microbial populations.
o Fertilisers rich in organic matter.
• Decomposing organic matter
Micro-organisms decompose plant remains, releasing humic and fulvic acids, essential for soil health.
By providing these food sources, growers can boost microbial activity, improving soil fertility and plant health.
Introducing the VGN line, Atami's new organic fertilisers.
As we have already said, one way to keep the soil well cared for and nourished is to provide organic matter that can be used by micro-organisms.
Because healthy soil is the basis for healthy plants, we have created the new VGN fertilisers. These certified fertilisers nourish your plant while caring for soil life, creating a healthy environment for the roots of your plants.
VGN Veganic fertilizer (5-2-2)
The high organic matter content of VGN 5-2-2 fertilizer not only feeds the plants, but also nourishes the micro-organisms in the soil. The positive effect of VGN 5-2-2 on soil life will enhance growth and lay the foundation for abundant and tasty harvests.
VGN Veganic fertilizer (2-2-4)
Because of its high organic matter content, VGN helps to promote a healthy soil ecosystem. VGN helps to promote a healthy soil ecosystem. Healthy soil is essential for healthy plants. VGN products will satisfy your organic requirements; try them and experience the difference for yourself!
VGN Veganic Boost (1-4-4)
The purpose of the VGN line is to nourish plants and support a thriving ecosystem below the surface. Like all other VGN products, all ingredients in VGN 1-4-4 are Control Union certified and approved for Organic Farming.
VGN CALMAG
Why choose VGN Calmag? This product blends the best ingredients, certified by Control Union and approved for organic farming, all without introducing nitrogen! VGN Calmag will not change the NPK ratio of your nutrient solution. Use it to correct imbalances and deficits in your solution in an easy, precise and natural way.
Our final thought
Without the billions of micro-organisms that exist in the soil food web, the plant kingdom would not thrive in the same way.
Mother Nature has created a never-ending process that allows old plant material and organic matter to become a source of food for beneficial micro-organisms and plants. This cycle, which has existed for thousands of years, will continue to exist even without human presence.
In terms of gardening practices, the use of microbes, fungi and probiotics has many advantages, from increased protection against pathogens or increased resistance, to increased plant health, nutrition and yield.
Depleted and unproductive soil or growing media can be made fertile and full of life again after inoculation with symbiotic micro-organisms or by adding more organic matter.
There is nothing wrong with adding these little helpers to your garden and letting them do the work for you and your plants.
