As we always explain to growers, the effectiveness of mycorrhizal fungi application is not always apparent. Soil microbes are living organisms, each with its own physiological and physical characteristics, much like plants, animals, and humans. They are influenced by nutrition, temperature, soil condition, symbiotic plant species, competition, and many other environmental factors. With so many factors affecting the quality and function of soil microbes, it can be challenging for growers to identify what applies to their specific case. However, as industry insiders, we feel obligated to provide a minimum guideline that can assist growers who may not have access to other resources.
[Soil Conditions That Diminish the Effectiveness of Endomycorrhizal Fungi]
The effectiveness of applying endomycorrhizal fungi can be diminished by soil conditions such as:
Mycorrhizal fungi rely heavily on carbohydrates to fuel their growth and metabolic processes. Their efficient absorption of carbohydrates can be attributed to their high respiration rates and active enzyme systems.
In nutrient-limited soil, adding nutrients can boost mycorrhizal biomass until the plant host is no longer resource-constrained. However, in nutrient-rich soil where plants have sufficient nitrogen and phosphorus, mycorrhizal biomass may decline as plants allocate less carbon belowground, making fungi carbon-limited. Although both plants and mycorrhizal fungi have minimum requirements for nitrogen and phosphorus, plants have a higher total demand for these nutrients.
The availability of plant carbon allocated belowground limits the growth of mycorrhizal fungi. When plants have enough nitrogen and phosphorus, they allocate less photosynthate belowground, leading to a reduction in mycorrhizal growth.
When soil nitrogen and phosphorus levels are very low, both plants and mycorrhizal fungi are nutrient-limited, so adding these resources can increase mycorrhizal growth. Conversely, at very high levels of nitrogen and phosphorus, neither plants nor fungi are limited by these elements, resulting in reduced mycorrhizal biomass as plants allocate more carbon aboveground to shoots and less belowground.
[Understanding the Relationship between Mycorrhizal Fungi and Plants: Importance of Matching Fungi to the Right Plant Species]
More than 80% of plant species have a symbiotic relationship with mycorrhizal fungi. The majority of these plant-fungi partnerships are classified as endomycorrhizal, while the remaining partnerships fall into the categories of ectomycorrhizal, ericoid, or orchid mycorrhizae. A document is available that provides examples of plants that form endo- and ecto-mycorrhizal associations, which may be helpful for further reference: https://extension.okstate.edu/fact-sheets/print-publications/hla/mycorrhizal-fungi-hla-6449.pdf
If mycorrhizal fungi are applied to non-mycorrhizal plants, the fungi may not form a symbiotic relationship with the roots of those plants. Non-mycorrhizal plants lack the necessary structures, such as specialized root cells, to accommodate mycorrhizal fungi. Therefore, the fungi may not be able to colonize the root system of non-mycorrhizal plants, and the plants may not experience any benefits from the fungi. In some cases, applying mycorrhizal fungi to non-mycorrhizal plants can even have negative effects, such as competition for resources or inhibition of root growth. It is important to match the right type of mycorrhizal fungi to the specific plant species to ensure that a beneficial symbiotic relationship can be established.
[Critical Factors Affecting the Effectiveness of Mycorrhizal Products]
There are several critical factors that can affect the effectiveness of a mycorrhizal product, regardless of its form (powder, granular, or liquid). These factors include:
Propagules have better survival rates than spores as they are already acclimatized to the soil conditions and can readily adapt to fluctuations in the environment and plant requirements. Additionally, propagules have higher infectivity rates than spores since they are in direct contact with the host plant and can overcome certain obstacles that spores need to overcome to form a symbiotic relationship.
Trichoderma, Bacillus, and other beneficial microbes can help mycorrhizal fungi propagate and prosper by improving soil biodiversity and soil health. These beneficial microbes can work in synergy with mycorrhizal fungi to enhance nutrient uptake, promote plant growth, and suppress plant pathogens.
Trichoderma and Bacillus are examples of soil bacteria that are known to have a positive effect on mycorrhizal fungi. These bacteria produce enzymes that can break down organic matter, releasing nutrients that mycorrhizal fungi can use for growth and development. In addition, these bacteria can help to create a more favorable soil environment for mycorrhizal fungi by suppressing plant pathogens and promoting the growth of other beneficial microbes.
The presence of mycorrhizal fungi and beneficial microbes in the soil can also help to improve soil health in general. Mycorrhizal fungi can form extensive networks of fungal hyphae that can improve soil structure and porosity, increase water-holding capacity, and reduce soil erosion. Beneficial microbes can also help to improve soil fertility by fixing nitrogen, cycling nutrients, and breaking down organic matter.
In general, the use of mycorrhizal fungi and beneficial microbes can help to create a more diverse and resilient soil ecosystem. This can lead to improved plant growth and health, increased crop yields, and a reduction in the need for synthetic fertilizers and pesticides. Additionally, by promoting soil health and biodiversity, the use of these beneficial microbes can contribute to the overall sustainability of agricultural and horticultural systems.
If you haven't had success with the applications of mycorrhizal fungi, you can refer to the checklists provided here to identify potential solutions. If you still need assistance, please contact us at firstname.lastname@example.org.
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