Mycorrhizal Fungi - A TerraSoil Overview

What are Mycorrhizal Fungi?

Mycorrhizal fungi form symbiotic associations with the roots of most terrestrial plants. These fungi enhance plant nutrient uptake, while plants supply the fungi with carbohydrates. Mycorrhizal fungi are classified into several types, with the most common being arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (EMF).

Difference Between Endomycorrhizal and Ectomycorrhizal Species

1. Endomycorrhizal Fungi (AMF): These fungi penetrate the root cells of the host plant, forming structures such as arbuscules and vesicles. AMF are associated with a wide range of plant species, including most agricultural crops.

2. Ectomycorrhizal Fungi (EMF): These fungi form a sheath around the roots and do not penetrate the root cells. EMF are primarily associated with woody plants, such as trees in temperate and boreal forests.

Factors Affecting Colonization of Roots

Several factors influence the colonization of plant roots by mycorrhizal fungi:

1. Soil Nutrient Levels: High levels of available phosphorus can inhibit mycorrhizal colonization as plants rely less on fungal partners for nutrient uptake.

2. Soil pH: Extreme pH levels (too acidic or too alkaline) can negatively affect fungal colonization.

3. Soil Structure and Moisture: Well-aerated, moist soils promote mycorrhizal colonization, while compacted or waterlogged soils hinder it.

4. Plant Species: Different plant species have varying degrees of dependency on mycorrhizal associations.

Effects of Symbiotic Relationship with Plants

The symbiotic relationship between mycorrhizal fungi and plants offers numerous benefits to both partners:

1. Nutrient Uptake: Mycorrhizal fungi enhance the uptake of nutrients such as phosphorus, nitrogen, and micronutrients from the soil.

2. Water Absorption: Fungal hyphae extend beyond the root zone, increasing the plant’s water absorption capacity.

3. Disease Resistance: Mycorrhizal associations can improve plant resistance to root pathogens.

4. Stress Tolerance: Plants with mycorrhizal associations are often more resilient to environmental stresses, such as drought and salinity.

Food Types Mycorrhizal Fungi Consume

Mycorrhizal fungi primarily consume carbohydrates provided by their host plants. These carbohydrates, mainly in the form of sugars, are essential for the growth and functioning of the fungi. In return, the fungi provide the plants with water and nutrients.

Specific Benefits Afforded to Plants

1. Enhanced Growth and Yield: Mycorrhizal fungi improve plant growth and yield by increasing nutrient and water uptake.

2. Improved Soil Structure: The extensive hyphal networks of mycorrhizal fungi help bind soil particles together, improving soil structure and reducing erosion.

3. Increased Root Mass and Biomass: Studies report that mycorrhizal associations can lead to significant increases in root mass and overall plant biomass. On average, plants with mycorrhizal associations can exhibit a 30-50% increase in root mass and a 20-40% increase in overall biomass.

How Mycorrhizal Fungi are Produced and Stored

Mycorrhizal fungi are typically produced in controlled environments, using host plants to encourage fungal growth. The inoculum, consisting of spores, hyphae, and colonized root fragments, is harvested and processed for storage. Fungi are stored in cool, dry conditions to maintain viability until application.

What Kills Mycorrhizal Fungi?

Several factors can kill or inhibit mycorrhizal fungi:

1. High Soil Fertility: Excessive use of chemical fertilizers, particularly phosphorus, can reduce mycorrhizal colonization.

2. Pesticides and Fungicides: Certain chemicals used in agriculture can be toxic to mycorrhizal fungi.

3. Soil Disturbance: Tillage and other forms of soil disturbance can damage fungal networks.

4. Extreme pH Levels: Soils that are too acidic or alkaline can be detrimental to mycorrhizal fungi.

The Fungal Network in Old Growth Forests

In old-growth forests, mycorrhizal fungi form extensive networks known as the "Wood Wide Web." These networks connect individual plants and trees, facilitating nutrient and water transfer, and enhancing the resilience of the forest ecosystem. Mycorrhizal networks in old-growth forests are vital for the survival of seedlings and the maintenance of biodiversity.

Conclusion

Mycorrhizal fungi are indispensable partners in plant growth and soil health. Understanding their roles, benefits, and the factors affecting their colonization can help in optimizing their use in agriculture and forestry. The intricate symbiosis between plants and mycorrhizal fungi underscores the importance of preserving and fostering these relationships for sustainable ecosystem management.

References

1. Smith, S. E., & Read, D. J. (2008). Mycorrhizal Symbiosis (3rd ed.). Academic Press.

2. van der Heijden, M. G., & Horton, T. R. (2009). "Socialism in soil? The importance of mycorrhizal fungal networks for facilitation in natural ecosystems." Journal of Ecology, 97(6), 1139-1150.

3. Brundrett, M. C. (2009). "Mycorrhizal associations: the web resource." Mycorrhiza, 19(6), 363-366.

4. Smith, F. A., & Smith, S. E. (2011). "Mycorrhizal symbiosis: pathways for carbon and phosphorus transfer." Trends in Plant Science, 16(10), 542-548.

5. Johnson, N. C., Graham, J. H., & Smith, F. A. (2013). "Functioning of mycorrhizal associations along the mutualism–parasitism continuum." New Phytologist, 135(4), 575-585.

6. van der Heijden, M. G. (2010). "Arbuscular mycorrhizal fungi as determinants of plant diversity: in search of underlying mechanisms and general principles." Mycorrhiza, 20(1), 1-9.

7. Courty, P. E., Buée, M., Diedhiou, A. G., Frey-Klett, P., Le Tacon, F., Rineau, F., ... & Garbaye, J. (2010). "The role of ectomycorrhizal communities in forest ecosystem processes: new perspectives and emerging concepts." Soil Biology and Biochemistry, 42(5), 677-678.

8. Bücking, H., & Kafle, A. (2015). "Role of arbuscular mycorrhizal fungi in the nitrogen uptake of plants: current knowledge and research gaps." Agronomy, 5(4), 587-612.

9. Smith, S. E., Facelli, E., Pope, S., & Smith, F. A. (2010). "Plant performance in stressful environments: interpreting new and established knowledge of the roles of arbuscular mycorrhizas." Plant and Soil, 326(1-2), 3-20.

10. Cairney, J. W. G. (2012). "Extramatrical mycelia of ectomycorrhizal fungi and their roles in nutrient cycling in forest soils." Soil Biology and Biochemistry, 57, 1031-1039.