By Rachel Boucher, B.Sc., University of Waterloo

Edited by Pedro M. Antunes, Ph.D., Algoma University and Maren Oelbermann, Ph.D., University of Waterloo

Arbuscular mycorrhizal (AM) fungi are extraordinary soil dwelling organisms found worldwide (Davison et al., 2015). They form associations with the roots of most plants, including important agricultural crops such as corn, soybeans, and wheat (Higo et al., 2018). The relationship between plants and AM fungi is a mutually beneficial symbiosis wherein the plants have greater access to nutrients and an improved tolerance to environmental stressors (e.g., drought, salt, pathogen attack) and the fungi are provided with a source of energy (e.g., carbon) (Kiers et al., 2011; Pepe et al., 2018). The fungal partner relies completely on this carbon directly provided by the plant host. Agronomically, the most conspicuous benefit of this relationship can be seen in increased grain yield when the soil is appropriately managed to increase the abundance of AM fungi (Brito et al., 2021; Oviatt & Rillig, 2021; Pellegrino & Bedini, 2014).

Most agricultural soils can be considered degraded as a result of modern farming practices such as intense tillage (Hussain et al., 2021). However, AM fungi can contribute to the improvement of soil quality by enhancing soil aggregation, soil organic matter, and water holding capacity (Thirkell et al., 2017). Additionally, AM fungi can help reduce soil erosion while also minimizing nutrient losses (Mardhiah et al., 2016; Thirkell et al., 2017; van der Heijden, 2010).  Overall, the appropriate management of AM fungi in agriculture can improve long-term crop production and food quality (Antunes et al., 2012).

AM fungi are used in the form of commercial inoculants that are produced by the agricultural industry (Hart et al., 2018). These inoculants are typically composed of a single exotic AM fungal strain that may not be adapted to local environmental conditions. This makes commercial inoculants less diverse and potentially less effective than the indigenous AM fungi community. In addition, a recent global evaluation of commercial AM fungal inoculants indicated that many of these products are ineffective (Salomon et al., 2022). The indigenous AM fungi community is already present in soils and is adapted to local/regional environmental conditions. However, agricultural management practices (e.g., intense tillage, herbicide, fungicide, and fertilizer application) negatively impact the indigenous AM fungal community by decreasing their diversity and quantity (Manoharan et al., 2017; Säle et al., 2015; Williams et al., 2017).  Additionally, the cultivation of non-mycorrhizal crops (e.g., canola) that do not associate with AM fungi can reduce abundance and thereby the effectiveness of AM fungi in subsequent mycorrhizal crops in the rotation (Hansen et al., 2019; Koide & Peoples, 2012). However, this provides an opportunity to restore and enhance the indigenous AM fungi community.

Our current research in northern Ontario evaluates the effectiveness of commercial inoculants compared to indigenous AM fungi inoculants under soybean production followed by canola. The goal of this research is to enhance on-farm indigenous AM fungi. This research will take place at two field sites in the Algoma district and one field site in New Liskeard. Sorghum-sudan grass, a highly mycorrhizal cover crop (Wang et al., 2019), was grown in a field adjacent to the main experimental site to promote the growth of indigenous AM fungi in the first year of this study. Meanwhile, the main experimental field site was planted to canola. In year 2, a thin layer of topsoil containing roots and rhizosphere soil obtained from the sorghum field will be used as indigenous AM fungi inoculum and incorporated on the main experimental field sites which will be planted to soybean. Throughout the growing season we will analyze various soil and crop metrics (e.g., soil nutrient content, crop yield, crop growth stages, soil microbial biomass, carbon, and nitrogen). We predict that on-farm augmentation of indigenous AM fungi using this method has the potential to replace commercial inoculants and increase soil quality and crop productivity while conserving the natural diversity of the soil. While AM fungi are widespread, current farming practices do not generally encourage their growth. We expect that this project can contribute to change this by optimising AM fungal diversity and abundance in soils and improve agroecosystems.

Thank you to Pedro M. Antunes, Maren Oelbermann, Josh Nasielski, Melinda  Drummond, Nathan Mountain, Mikala Parr, and David Thompson, as well as OMAFRA and RAIN for all of their contributions to this project. This project is supported by Algoma University, University of Guelph, and the University of Waterloo.

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