Mycorrhizal fungi: for a better harvest

What do you know about mycorrhizal fungi?

Mycorrhizal fungi help plants take up water and nutrients more effectively and accumulate carbon dioxide, improving both yield and crop quality. In this article, we explore the types of mycorrhiza found in nature, how mycorrhizal symbiosis works and why mycorrhizal fungi are not all alike, even when they belong to the same species.

A mycorrhizal fungus forms a long-term symbiotic relationship with a plant and stimulates root-system development, increasing water and nutrient uptake in exchange for carbohydrates produced through photosynthesis. This mutually beneficial relationship improves water and nutrient uptake and, consequently, increases yield.

Types of microorganisms found in soil

Soil contains different types of microorganisms, which can be distinguished by their relationship with plants:

Saprophytic: Fungi, bacteria and other microorganisms that break down lignin and cellulose in dead plants. This helps release nutrients that other plants need for growth.
Pathogenic: These microorganisms obtain nutrients from living plants, weakening and sometimes killing them.
Symbiotic: These also obtain nutrients from living plants, but unlike pathogenic microorganisms, they form a mutually beneficial relationship.

Mycorrhizal fungi and their types

There are 2 types of mycorrhiza:

Ectomycorrhiza: Fungal hyphae — microscopic, branched or unbranched threads that form part of the fungal vegetative body — create a mantle around the plant’s roots without penetrating the cell walls. Instead, the hyphae grow in the spaces between cells in the outer root layers.
Endomycorrhiza: The hyphae penetrate root cells and form structures called arbuscules. These are the sites where the fungus exchanges nutrients with the roots for carbon.

How does mycorrhizal symbiosis work?

The mycorrhizal fungus supplies the plant with water and nutrients such as phosphorus, potassium, calcium, iron, zinc, magnesium and manganese. In return, it receives a small amount of the carbohydrates produced by the plant through photosynthesis. In particular, it receives triose phosphate derived from sucrose, which the fungus cannot synthesise on its own.

Root hairs must be present for the mycorrhizal fungus to colonise the root system and begin functioning. The fungus then establishes itself in plant cells and forms arbuscules, where it exchanges water and nutrients for photosynthetic carbohydrates. It grows beyond the root, extending a network of hyphae that absorbs water and nutrients and transports them to the arbuscules. To obtain more water and nutrients, the plant develops more absorbing roots, while the fungus grows and forms further connections with the plant. Together, these processes increase root biomass. It has been estimated that 7-250 fungal hyphae develop for every metre of root.

Nutrients move through the hyphae within vesicles — small, vacuole-like structures in which nutrients are stored. For example, a hypha takes up phosphorus as orthophosphate, which then accumulates in a vesicle as polyphosphate. This differs from the way plants absorb phosphorus. The distinction is important because phosphorus is tightly bound to soil particles.

Mycorrhizal fungi stimulate auxin secretion in the plant. Auxins are a class of hormones directly associated with root-system development and increased root-hair formation. Because the fungus colonises the plant through root hairs, as noted above, an increase in root hairs allows it to establish more connections and continue expanding.

Another benefit of the symbiotic relationship between a plant and mycorrhizal fungi is improved photosynthesis, allowing the plant to accumulate more carbon dioxide. This, in turn, improves the exchange of nutrients and water through a greater number of arbuscules in the root system.

How does mycorrhizal symbiosis benefit the plant?

Plants take up carbon dioxide through the stomata in their leaves. An increased ability to absorb and accumulate carbon dioxide means they can produce more photosynthates. Fruit-bearing plants can consequently synthesise more carbohydrates to support fruit development.

Greater photosynthetic activity allows plants to increase their biomass and root-system volume. They become greener and more resilient, with a larger root system.

When plants can accumulate more carbon dioxide, this not only helps reduce its release into the atmosphere but also makes metabolic processes more efficient. In other words, the plant can produce more with fewer resources by making better use of what is available.

The more CO2 a plant accumulates, the less water it uses to produce the same amount of biomass, improving water-use efficiency (WUE). A better-developed root system also allows the plant to absorb nutrients with less energy. Roots can explore a larger volume of soil, and this, together with fungal activity, increases nutrient uptake at a lower energy cost. Put simply, it improves nutrient-use efficiency (NUE).

A unique fungus: GLOMUS IRANICUM VAR. TENUIHYPHARUM

Mycorrhizal symbiosis clearly benefits fruit-bearing plants. However, many fungal species in the soil form mycorrhiza. Do they all have the same effects and characteristics?

The answer is no. Fungi may belong to the same species without having identical characteristics. This is why it is important to understand the different strains and their specific properties.

Symborg has worked for more than 10 years with a unique fungus known as Glomus iranicum var. tenuihypharum, which has distinctive characteristics:

It produces an extramatrical mycelium 4 times larger than that of other fungi. A 4-fold increase in this network allows the fungus to explore more soil, absorb more nutrients and transport them to the plant more quickly. The mycorrhizal fungus can rapidly produce 7-250 metres of hyphae for every 1 metre of root system.
It reproduces outside the root through very small spores. The smaller spore size — 30 microns, compared with 100 microns in other fungi — and spore production outside the root improve its relationship with the plant. Spores are one of the most important means of fungal reproduction, and most fungi that form arbuscular mycorrhiza produce spores inside the roots.
Its salt tolerance is 2 times greater than that of other fungi. It is also compatible with various highly concentrated fertilisers available on the market.

The fungus also improves soil structure. Its hyphae and filaments help soil particles aggregate by releasing a protein called glomalin.

In summary, nature provides the answers, and Symborg turns them into practical solutions. The company offers biological products based on microorganisms — in this case, a unique strain of mycorrhizal fungus — to help farmers meet the challenges of modern agriculture and achieve productive harvests.

Products containing mycorrhizal fungi from the Symborg catalogue:

Mycoup

A uniquely formulated biostimulant containing the mycorrhizal fungus Glomus iranicum var. tenuihypharum, which forms a symbiotic relationship with the plant and increases yield and productivity.

Mycoup 360

A biostimulant containing the mycorrhizal fungus Glomus iranicum var. tenuihypharum and mineral complex 360, which contains iron oxide (Fe2O3). In addition to the fungus’s symbiotic relationship with the plant, the iron oxide protects roots against nematodes and breaks down their chitin.

Resid HC

A biostimulant based on the mycorrhizal fungus Glomus iranicum var. tenuihypharum, specially developed for treating cereal seeds.

Resid MG

A microgranular biostimulant containing the mycorrhizal fungus Glomus iranicum var. tenuihypharum.