Christopher Tolis '21, Karit Matanachai '22

What is Arbuscular Mycorrhizal Fungi?

When people think of fungi, many imagine a mushroom in the middle of a damp forest feeding off of dead matter; however, most do not realize that fungi can also be beneficial. In fact, arbuscular mycorrhizal fungi (AMF) forms one of the most important symbioses on the planet given that it allows plants to thrive in unfavorable conditions. This symbiosis, a mutually beneficial bond, occurs between AMF and a variety of plants such as soybeans and wheat. In this relationship, AMF receives carbon and sugars for growth while the plant increases its nutrient absorption rate. To increase a plant’s range, AMF have white filamentous strands called hyphae which act as tentacles to increase the surface area of absorption.

Apart from increasing surface area, AMF can also break down substances that would otherwise be insoluble for the plant. For example, phosphorus, an essential building block of life, is often found in an inorganic form which makes it impossible for plants to use. AMF can break down these inorganic compounds by indirectly secreting phosphate-solubilizing enzymes, allowing plants in nutrient-deficient environments to survive. Similarly, some plants rely on AMF for nitrogen fixation as it is usually found in its insoluble form.

Why is it important?

Around the world, farmers apply chemicals at an increasing rate to improve their crop yield. For instance, if farmers need to replant while lacking the proper time and nutrients to revitalize the soil, the yield will decrease, forcing them to apply more and more chemical fertilizers. These fertilizers become runoff chemicals that are swept into nearby streams, thereby contaminating them. Using AMF as a substitute for fertilizers would ensure soil sustainability and reduce the environmental impacts of farming.

How is AMF used as a biofertilizer?

AMF is applied by removing fungal hyphae and surrounding soil from the roots of plants that already support AMF colonies and transplanting them into unfertilized soil. Once this process is complete, AMF remain on plant communities indefinitely, eliminating the need for yearly reapplication. Healthy AMF colonies then populate the roots of neighboring plants, making small scale application feasible. Instead of incolulating a whole field, farmers can apply AMF to an isolated portion of land, from which AMF will gradually disseminate.

The ability of AMF to enhance root nutrient uptake greatly decreases the need for environmentally harmful fertilizers. It also makes fertilizer that is used more effective. A study in which rice crops were inoculated with AMF concluded that 25%-50% less fertilizer was required to yield 10% more grains than using only fertilizer.

The production of AMF biofertilizer

AMF are obligate symbionts: they are unable to grow in the absence of a host plant, hence causing difficulty in their production. AMF used for inoculation are propagated on trap plants which host high concentrations of numerous fungal species. Aquaponics is another method of AMF production and is a candidate for large scale production because it simulates ideal growing conditions and yields isolated spores.

Conclusion

The use of AMF fertilization is a very effective method of increasing crop yields while greatly reducing fertilizer use and pollution. It is becoming more prolific in Europe and North America, but it is not used where it is most needed. Many developing countries have soils with low phosphorus content, and the use of traditional fertilizers is limited by cost. There is a great need for accessible methods of producing and applying AMF that would enhance crop growth in developing countries.

Bibliography

Berruti, Andrea, Erica Lumini, Raffaella Balestrini, and Valeria Bianciotto."Arbuscular Mycorrhizal Fungi as Natural Biofertilizers: Let's Benefit from past Successes." Frontiers in Microbiology. Last modified January 19, 2016. Accessed September 1, 2020. https://www.frontiersin.org/articles/10.3389/fmicb.2015.01559/full.

Hyphae are comprised of hypha, which are the long filamentous branches found in fungi and actinobacteria. Photograph. Accessed September 1, 2020. https://biologydictionary.net/hyphae/.

Roy-Bolduc, Alice, and Mohamed Hijri. The Use of Mycorrhizae to Enhance Phosphorus Uptake: A Way out the Phosphorus Crisis. Journal of Biofertilizers & Biopesticides, 2010. Accessed September 2, 2020. https://www.longdom.org/open-access/the-use-of-mycorrhizae-to-enhance-phosphorus-uptake-a-way-out-the-phosphorus-crisis-2155-6202.1000104.pdf.