Mycorrhizal Fungi and Plants: Benefits, Risks, and What Gardeners Should Know

While plants need the soil to provide them with nutrients, they aren't able to utilize nutrients in all soil. This is where arbuscular mycorrhizal fungi (AMF) may be of great benefit. These small soil bugs bring the plants closer to the soil, increasing the plants ability to absorb nutrients, such as phosphorus uptake by mycorrhizal fungi.

The mycorrhizal association with plants seems to be a symbiotic association which benefits both the mycorrhizal fungi and plants. Mutualisms between fungi and plants help plants to take up nutrients and plants contribute photosynthetically generated carbon to help fungus grow. However, how can we determine, does more nutrient uptake imply more plant growth, plant production?

To test this, a study from 2025 looked at the fungal community in conventionally farmed areas of agriculture and the adjacent grasslands. The mycorrhizal fungi from agricultural field inocula did not consistently yield higher concentrations of the nutrient in the plant tissue relative to the grassland inocula. The plant growth, on the other hand, did seem to provide slightly less mycorrhizal fungi benefits than did the grassland inocula.

The results give a more complex and detailed description of the function and relationship of mycorrhizal fungi and plants with the growth of plants. Measuring what plants take in is not the only consideration that scientists are making while weighing costs and benefits of plant/fungus partnerships, however, since they must also account for the amount of carbon that plants themselves pump into their fungal partners, and what this may mean for the plant's growth.

What are mycorrhizal fungi benefits to plants?

Arbuscular Mycorrhizal Symbiosis 

In most plants there are arbuscular mycorrhizal fungi in the roots. They develop a specialised structure in the roots referred to as an arbuscule and are characterized with the transfer of the nutrients between the fungus and plant. The fine strands (hyphae) of fungi colonise the soil around plants that have roots.

They are also very small compared to roots, and can gather about small nutrient patches and soil pores which are concealed from the roots. This may result in greater flow of nutrients to the plant including greater immobile nutrient flow, or soil phosphorus for instance.

Phosphorus is used for energy transfer, root development and other vital plant functions. The elements of a protein and enzymes require nitrogen, as do elements of chlorophyll and other plant growth components. Fungi may absorb both nutrients but mycorrhizal fungi benefits are dependent on soil conditions, community of the fungi, and nutritional needs of the plants.

The mechanisms account for some of the mycorrhizal fungi and plant benefits, such as in soils which are nutritionally stressed by root uptake. The benefit available, however, varies with the type of fungus, type of plant and growing conditions.

The two-way exchange between plants and fungi

The mycorrhizal fungi symbiotic relationship in nature and there is an exchange of resources. The fungal hyphae obtain nutrients from the soil and send some of those nutrients to the host plant. In response the plant provides carbon based products created during its photosynthesis process.

It is not the same for both parties when it comes to sharing. The fungi need resources to grow and to obtain nutrients . The plant tree needs to be investing some of its photo-generated carbs at the ground level. If the nutrients received are adequate to stimulate the growth sufficiently, the association can be beneficial to the plant. The net benefit may be smaller if the carbon investment is quite high relative to the "growth response".

This balance is important for understanding mycorrhizal symbiosis in plants. The important question is not whether the fungus is giving nutrition to the plant, but whether it's improving the performance of the plant in the environment in which it lives.

Does Management of Agriculture Impact Mycorrhizal Fungal Functions?

Agricultural fields – suitable for unfertilized grasslands

There are changes in soil microorganisms, including mycorrhizal fungi and plant growth, that can be caused by agricultural management. Prescribed practices such as tillage, mineral fertiliser application, continuous crops, and some pesticide management practices can change the factors that allow fungi to survive and grow.

Buil et al. (2025) analyzed the monoculture area of a conventionally managed arable crop and the surrounding semi-natural grasslands from four comparable field sites in the Czech Republic. Pastures had light disturbance and were not fertilised, and the fields were periodically ploughed and fertilized with mineral substances.

The scientists wondered if these variability in management history had different effects on the fungal function. They wanted to determine if the two environments led to similar benefits for the plants or if there were differences in how they acquired nutrients and in their carbon needs.

The current research could also be important in agricultural soils since it implies that differences in management history may align fungal communities in ways that impact their activity, even after these communities are subjected to the same experimental conditions.

Mycorrhizal Performance was tested by the Researchers

The scientists chose this herbaceous species, ribwort plantain (Plantago lanceolata), as their model host. They were cultivated in a glass house on both types of sterile soils–agricultural fields and grasslands.

Three inoculation treatments were used in the experiment: treatments with agricultural field, grassland, and non-mycorrhizal fungal inocula. These treatments in addition to both the soil origins allowed for both types of origin (inoculum and soil) to be distinguished.

They also employed labelled atoms of phosphorus, nitrogen and carbon to follow the movement of these resources in the plant–soil system. The information given by these tracers was unavailable with just size measurements.

While the experiment provides valuable information for soil management and mycorrhizal fungi and plants, it is recommended to keep in mind that the researchers engaged in this study were growing a model plant, in a controlled greenhouse environment. The results are not automatically the prediction of the yield from all agricultural systems.

Promoting more phosphorus in the soil does not necessarily produce better growth for plants

The results of the study on how plants grow Summary

Plants inoculated with fungal communities from grasslands tended to have a greater positive growth response compared to plants inoculated with functional communities from agricultural fields. This difference is significant because plant biomass is an indicator of the association's bottom line. It reflects the levels of nutrients, carbon costs and other plant growth factors.

Based on the experiment results, it can be said that the agricultural-field inocula were less desirable regarding growth promotion in the tested environment. But it does not imply that all the fungi in agriculture are inimical or that all the grassland communities will always do well. The answer also had different variations across the experimental sites.

Phosphorus accumulation in systems

Interpretations cannot be problem-free if it is impossible to separate the concentration of phosphorus uptake by mycorrhizal fungi from the total accumulation. Concentration of phosphorus is the amount of phosphorus relative to a certain amount of plant tissue. The total phosphorus content, however, is the total amount that has been accumulated by the plant biomass.

Thus, a plant with low biomass may have a higher concentration of phosphorus without accumulating a large total amount of phosphorus. However, a low concentration of phosphorus may exist in the tissues of a larger plant and still give a high total phosphorus.

The agricultural-field inocula gave greater increases in phosphorus concentration in shoots and roots than did the grassland inocula in the study. The researchers, however, did not detect significant differences in overall phosphorus concentration in the plants from the various origins of the inoculum or in the ability to absorb the labelled compartment of the phosphorus from the origin of the nutrient.

It is important to note the relevance of this difference in account for the ability of mycorrhizal fungi and plant growth to uptake phosphorus. These higher levels of tissue phosphorus does not necessarily equate to more total soil phosphorus, etc., contribution to the host tissue by the fungal community.

The implications of these findings

The researchers also hypothesized that this higher phosphorus level was not reflected in increased biomass because other resources were limiting growth. Nitrogen limitation was also likely in this experiment and higher carbon demands were also thought to decrease the net beneficial effects of agricultural field inocula.

The practical lesson is to measure not only the nutrient concentration for those researchers who are evaluating mycorrhizal fungi nutrient uptake. Biomass, nutrient pool and fluxes between different components of the system are complementary.

The study also shows the importance of taking a single measurement to only obtain part of the story about mycorrhizal fungi and vegetation. While it is important to acquire nutrients, its benefit is determined by the plant's ability to utilize nutrients for subsequent development.

Faster Nitrogen Acquisition Does Not Guarantee Greater Plant mycorrhizal fungi benefits

Use of isotope tracing to monitor nitrogen movement

The scientists divided each pot into two based on missing nutrients to examine nitrogen movement. A very fine mesh was used so that the plant roots would not get in the compartment, while allowing the fungal hyphae to enter.

Scientists fed a stable nitrogen isotope, N-15 (otherwise known as N-15). They could monitor the movement of nitrogen within the system after it was introduced to the plants' shoots, roots and soil compartments by measuring the amount of the label present.

This method gave information on nutrient transport besides on the total amount of nitrogen in the plant.

What the Seven-Day Measurements Revealed

Agricultural field inoculants used up the labelled material sooner than the grassland inoculant. They also had higher shoot N assimilation compared to the grassland inocula in the short-term tracer experiment.

The differences in these results indicate variation in the fungal communities' rate of access and turnover of N in the soil/plant system. Moving a source of nutrients from a more localised zone will not always mean that more nitrogen is available for the plant in the long term.

The overall study results were lacking in significant differences between the origins of inoculant and effect on total plant nitrogen. The results suggest not that agricultural-field fungi had a greater total N benefit but that the nutrient-transfer dynamics differed.

Nutrient Transport vs. Net Plant Benefit

Nutrients may be located in plant organs, roots, fungi, and the surrounding soil. Not all the material will get to the shoots, nor will the amount be the same as originally picked up by soils.

Overall the study revealed that the mycorrhizal plants were able to maintain more radiolabeled- N in roots and root zone soil with less in the shoots than in non-mycorrhizal plants. Some nitrogen has been found to have been temporarily immobilized in fungal structures and/or the soil system, the researchers noted.

The implications of this man's knowledge are why the ability of mycorrhiza to take up nutrients and transfer them to cells quickly does not guarantee improved plant growth. The processes of nutrient acquisition, transfer and allocation are distinct and can affect the final outcome.

A breakdown of the cost of mycorrhizal fungi in carbon

Plants invest in fungi in order to hedge their bet

The mycorrhizal fungi and plants are arthropods which are unable to fixate the carbon via photosynthesis. They are heterotrophic, growing on carbon compounds produced by their host plants which they use to extend and maintain their hyphae and other structures.

Now this is a normal way to make it around here, to carry the carbon like that; that's a part of being in the association. When the researchers try to value the advantages of the symbiosis in terms of net profits, it needs to outdo the costs of the plant (the nourishment benefit).

An additional component of mycorrhizal fungi carbon cost  and how this is shared between the mycorrhizal fungi and the plant. It may vary depending on the type of fungi, the different species of plants, soil characteristics and nutrient levels.

What Carbon Tracing Revealed

Plants were grown under CO2 that contained the stable isotope carbon-13 (^13C). They then were able to determine the distribution of the labeled carbon in the shoots, roots, and soil.

The soil in agricultural fields showed a higher percentage of recently fixed labelled carbon than did the soil in the grasslands. The authors concluded that this trend would support fungal communities in agricultural fields that have a higher carbon demand.

It suggests that these communities may have had relatively small growth impacts despite their relatively large impacts on phosphorus concentration and high nitrogen acquisition rates, as suggested by their puzzle.

Does More Carbon in the Below-Ground Torg a Higher Fungal Carbon Cost?

The outcomes do not need to be interpreted in a straightforward manner. Root exudates and fungal activity are among the sources of carbon that are detected in the soil. It was difficult to isolate specifically distributed carbon in the fungal hyphae from the carbon released from roots.

Therefore, it is not appropriate to regard increased carbon uptake by soil as a direct assessment of the actual carbon price which can be charged for the activity of the fungi. The researchers offered greater fungal carbon demand as a possible explanation of their results but noted that other microorganisms and processes involving roots each could have made a contribution.

It is important to recognize this for those working on the mycorrhizal fungi carbon-cost study. The amount of carbon allocated to soil is informative but further studies will be necessary to accurately measure the ‘fungal proportion' of the C.

What is the best system to determine the effectiveness of mycorrhizas?

Harvest Plant Growth and Nutrient Responsive Responses at the same time.

The biomass of the shoot, root, nutrient levels and total nutrient yields should be all included in a good assessment. These measurements indicate whether or not a fungus stimulates or inhibits the growth of the plant(s) and if either nutrient concentration increased or decreased, there was an increase or decrease in the total nutrient available in the plant(s).

Increase in one nutrient alone is not indicative of increased overall plant performance. Growth may be restricted by other nutrients, water availability, light or carbon availability.

Study the Concept of Nutrient Acquisition and Allocation

The rates of acquisition of nutrients by the bacterium, the transfer to plant tissues and the distribution between the shoots, roots, fungal structures and soil should be taken into account when considering the nutrients.

Isotope tracing may aid in differentiation. Short-term tracer measurements would, however, only provide information on nutrient transport during a specific period, and would not necessarily provide the exact information about long-term nutrient supply.

When evaluating the effectiveness of mycorrhizal inocula, these factors must be taken into account. Access to quick nutrients may not be the same plant biomass and/ or the strongest long term benefit when compared to a slower rate of access.

Why Carbon Investment and Experimental Limitations are included

Besides this another component of mycorrhizal performance is the source of the carbon plants provide it with. Researchers need to consider the cost of increased nutrient benefits being balanced by increased allocation of carbon underground for fungal communities.

They should also be aware of the presence of complex Souza's microbial communities and just single strains of fungi. The scientists tried to control for the background microbial communities but were not able to completely remove other microorganisms from the study.

As well, the same colonisation even becomes the same or similarity does not necessarily lead to the same function. There are two fungal communities that can be in root occupation to a similar level to each other but with different nutrient acquisition, nutrient allocation, and carbon demand.

Compared with root colonisation and nutrient concentration alone these measures offer a more comprehensive evaluation of the mycorrhizal fungi benefits.

What can this research contribute to sustainable agriculture?

Agricultural-field mycorrhizal communities had different effects on plant nutrient acquisition than grassland communities but resulted in no greater plant growth benefits in the 2025 study. This is the reason that mycorrhizal inoculants need to be tested with respect to plant growth, nutrient level and root colonization under specific crop conditions.

Farmers and gardeners can use commercial products, such as Mycoryx (produced by Novobac), a mycorrhizal inoculant consisting of Rhizophagus irregularis, an arbuscular mycorrhizal fungus. The manufacturer says that it is intended for colonizing roots and will allow plants to tap into water and nutrients beyond the root zone.

This study, however, did not test Mycoryx and thus its effectiveness cannot be determined. The study also provides no support for the transfer of grassland soils to fields directly. In general, a multi-leveled approach to sustainable agriculture is needed with effective management of soil health and availability of nutrients, as well as beneficial microbial communities; and using evidence to inform choices of inoculants.

Research Reference:

• Buil, P. A., Jansa, J., Rozmoš, M., Kotianová, M., Bukovská, P., Grilli, G., Marro, N., and Janoušková, M. (2025). “Soil cropping selects for nutrient efficient but more costly indigenous mycorrhizal fungal communities.” Biology and Fertility of Soils, 61, 841–859.