As part of the goal to achieve an increase in the world’s agricultural production to meet the needs of a growing global population, farmers and researchers alike must consider the sustainable intensification of agriculture.
To intensify agricultural systems, we must consider improving the amount of production knowledge per hectare – both above and below the soil surface (Rillig et al., 2016). A major, yet relatively misunderstood component of sustainable agricultural intensification is mycorrhizal fungi.
The word mycorrhiza comes from the Greek words mycos meaning fungi, and rhiza meaning soil.
Thus, mycorrhizal fungi are a classification of fungi that grows within the soil. Most notably, this type of fungi often forms symbiotic relationships with plants. Two distinct forms of mycorrhiza exist: ectomycorrhiza which remains outside plant cells, and endomycorrhiza in which part of the fungi exists inside the plant cell (Parniske, 2008).
Of all mycorrhiza fungi, the arbuscular mycorrhiza (AM) (a relationship between plants and members of an ancient phylum of fungi – Glomeromycota) is the most widespread terrestrial symbiosis, forming relationships with 70 – 90% of all land plant species (Parniske, 2008). For the purposes of agriculture, AM fungi is the most important mycorrhiza to research and incorporate its management into farming practices.
During AM fungi’s evolution, its ability to degrade carbon compounds was lost, preventing them from becoming a pathogen to host plant (Rillig et al., 2016). This interesting trait allowed AM fungi to form relationships with plants within the plant cell, leading to a symbiosis in which the fungi improves the supply of water and nutrients, such as phosphate and nitrogen, to the plant. In return the plant provides up to 20% of fixed carbon to the fungi (Parniske, 2008).
In theory, this contribution to the plant should allow to grow roots deeper into the soil, retrieving more nutrients and thus allow it to grow stronger and increase yields for agricultural crops. Furthermore, AM fungi increases drought resistance of host plants via its ability to improve water uptake (Altieri, Nicholls, Henao, & Lana, 2015). The properties of AM fungi are understood, however, the degree of their contribution to increasing yields and sustaining production relative to other soil properties is not completely understood and would require further research in complex soil relationships to fully understand.
Research on potato production has demonstrated that inoculation of AM fungi strains produces significant increases in yields. In a large trial, yields increased from 38.3 tons/ha to 42.2 tons/ha when the crops were inoculated with AM fungi (Hijri, 2016). This indicates that inoculation is a valid form of mycorrhiza technology available to farmers looking to increase their yields via natural processes. Other technologies (in the form of management practices) include basic pillars of conservation agriculture: no-till practices, continuous crop cover, and diversification practices (FAO, 2015). Some agricultural practices can have deleterious affects on AM fungal abundance and diversity (Rillig et al., 2016).
Responses of AM fungi to soil stoichiometry (soil chemical balance) is often species specific, therefore it is difficult to predict how AM fungi will react to the introduction of new plant species, bacteria, and other organisms that play a role in soil chemistry. In the future, direct measurements of mycorrhiza abundance may be available to farmers, allowing them to make precise responses to fluctuation in such abundance. This ability in combination with an accessible dataset may provide a major tool for farmers worldwide, by providing a rich and detailed source of field-tested mycorrhizal knowledge. A lack of field-based technologies is the largest bottleneck preventing this explosion in intensification abilities of farmers.
Currently available to farmers wishing to improve the abundance and diversity of mycorrhizal fungi are basic technologies and practices including: a diversity of mycorrhizae strain inoculants, no-tillage practices, diversification at a species, farm, and landscape level, as well as cover-cropping. In recent travels, I have discovered that some farmers are using trenches filled with logs, twigs and other organic scrap material, covered with soil. The farmers allow the material to decompose and become a rich source of fungi within the soil that can travel through the soil into areas where soil is being disturbed by harvesting practices. This allows soil that may be subjected to a decrease in fungi abundance to be quickly replenished by the nearby fungi-rich sources.
Mycorrhiza fungi and particularly AM fungi requires further research to explore its full potential but based on our current understanding, it appears that mycorrhizal knowledge and technology is the next step in organic and sustainable agricultural intensification. This revolution may provide a simple solution to increasing yields and profit per unit area, benefitting both farmers and the global population in the long term.
About the Author
Jayden Kuzdak-Hubbs is a recent graduate from the University of Toronto at Mississauga, studying environmental science and biology, with particular interests in sustainable agriculture. As part of his 4th year thesis, in August 2018, Jayden travelled to Ecuador to research the agricultural adaptations to climate change and the enhancement of agroecosystem resilience to climate impacts. Jayden continues to explore his passion by keeping up-to date on new agricultural research and seeks a career in improving the sustainability of global agriculture.
References:
Altieri, M. A., Nicholls, C. I., Henao, A., & Lana, M. A. (2015). Agroecology and the design of climate change-resilient farming systems. Agronomy for Sustainable Development, 35(3), 869–890. https://doi.org/10.1007/s13593-015-0285-2
FAO, (2015). Conservation Agriculture. Available online at: http://www.fao.org/ag/ ca/index.htm
Hijri, M. (2016). Analysis of a large dataset of mycorrhiza inoculation field trials on potato shows highly significant increases in yield. Mycorrhiza, 26(3), 209–214. https://doi.org/10.1007/s00572-015-0661-4
Parniske, M. (2008). Arbuscular mycorrhiza: The mother of plant root endosymbioses. Nature Reviews Microbiology. https://doi.org/10.1038/nrmicro1987
Rillig, M. C., Sosa-Hernández, M. A., Roy, J., Aguilar-Trigueros, C. A., Vályi, K., & Lehmann, A. (2016). Towards an Integrated Mycorrhizal Technology: Harnessing Mycorrhiza for Sustainable Intensification in Agriculture. Frontiers in Plant Science, 7(October), 1–5. https://doi.org/10.3389/fpls.2016.01625