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Organic Agriculture Centre of Canada

As public concerns fuel the formation of policies aimed at lessening the environmental impacts of Canada’s agricultural industry, the critical role of arbuscular mycorrhizal fungi (AMF) in sustainable, low-input agricultural systems becomes increasingly significant. Previously dismissed as a microorganism whose unpredictable contribution to crop productivity could be easily replaced with the use of fertilizer, AMF have been recently recognized by researchers Chantal Hamel and Desire-Georges Strullu in their publication, "", as the very backbone of a soil system’s health and productivity.  Compiling an impressive array of research in defence of AMF’s immutable importance, the authors have created a document that will likely convince Canada’s farmers and policy makers to adopt both the management practices and future technologies necessary to enhance AMF’s populations and performance.

During a recent phone interview, Chantal Hamel noted that "unlike human beings, plants cannot walk away from their problems." As a result, they have developed complex relationships with other members of the soil community, the consequences of which ensure not only their own survival but the strength and well-being of the surrounding soil ecosystem. AMF, for example, in return for a supply of carbon and energy, will stimulate a host plant’s ability to uptake water and nutrients, resist disease, tolerate drought and will, ultimately, improve its productive capabilities. Then, as the fungi spread out from the plants through the soil they form hyphal networks that have been associated with increased soil organic matter and stable soil aggregates: properties indicative of improved soil physical structure. With as many as 30 million AMF performing these multitudinous tasks in every gram of suitable soil one soon realizes the tremendous agricultural potential of these organisms.

Unfortunately, for reasons both cultural and environmental, not all soils are conducive to optimal AMF expression. As Hamel and Strullu note, "the mycorrhizal effects depend on the plant and AMF genotypes interaction, as well as on soil conditions." The authors then cite several studies that highlight the consequences of this interdependence. For example, a study conducted in a phosphorous rich field (phosphorous being traditionally equated with poor AMF development) measured the growth responses of different strawberry cultivars inoculated with one strain of arbuscular mycorrhizal fungi (Stewart et al. 2005).  Interestingly enough the growth rate of some of the plants was decreased while others were considerably increased: results that highlight both the intricate nature of AMF ecology and the need for a holistic approach to future AMF management.

In response, scientists like Chantal Hamel of Agriculture and Agri-Food Canada are working towards future arbuscular mycorrhizal genotypes that will enhance crop production in Canada. Chantal, stationed at the Semiarid Prairie Agricultural Research Centre, has been working, primarily, on wheat breeding programs aimed at optimizing wheat-AMF symbiosis. By recording the soil type, temperature, metal content and local weather of a given region, Chantal and her fellow researchers are creating models that identify AMF strains in a specific area. Once identified, the researchers will start the process of breeding plants designed to effectively interact with local AMF in order to efficiently and cost-effectively increase crop yield.

Chantal is also working with members of the Organic Science Cluster, a program developed by the Organic Agriculture Center of Canada and funded by Agriculture Canada’s Growing Forward program, to develop programs that will give farmers the necessary tools to manage mycorrhizal fungi in their soils. Fortunately, many of the recommended management practices are already utilized by organic producers: minimal use of chemical fertilizers, especially those high in phosphorous, enhanced AMF population and crop productivity; cover cropping and crop rotations to encourage the development of diverse AMF communities that more effectively interact with subsequent crops; and reduced or shallow tillage operations to lessen the damage to existing AMF hyphal and mycelia networks.  Chantal is also hoping that improved soil testing techniques in the future will help farmers to identify and, therefore, efficiently utilize the specific AMF strains found in their fields.

Arbuscular mycorrhizal fungi have existed, largely unchanged, for over 400 million years. Linked to the land colonization of plants, their evolutionary and ecological importance is undeniable. In North America, however, limited AMF research has been conducted, likely due, in part, to the relatively recent rise of highly mechanized, intensively managed agricultural systems that operate independently of naturally occurring soil biological interactions. Fortunately, as public concerns related to agriculture’s environmental impacts motivate governments to modify current agricultural practices, researchers like Hamel and Strullu are looking to the seemingly endless potential of arbuscular mycorrhizal fungi to develop agricultural systems that are productive, efficient and sustainable.

Reference
Stewart, L. I., Hamel, C., Hogue, R. and Moutoglis, P. 2005. Response of strawberry to inoculation with arbuscular mycorrhizal fungi under very high soil phosphorus conditions. Mycorrhiza 15: 612–619.

This article was written by Tanya Brouwers on behalf of the OACC with funding provided by Canada’s Organic Science Cluster (a part of the Canadian Agri-Science Clusters Initiative of Agriculture and Agri-Food Canada's Growing Forward Policy Framework).  The Organic Science Cluster is a collaborative effort led jointly by the OACC, the and industry partners. For more information: oacc@dal.ca or 902-893-7256.

Posted July 2010