Assessment of Arbuscular Mycorrhizal Fungal Inoculants for Pulse Crop Production Systems

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The introduction of commercially available arbuscular mycorrhizae (AMF) inoculants holds significant promise for use in pulse crop production systems. Effective AMF associations are known to enhance uptake of relatively immobile nutrients such as phosphorus and various micronutrients, and are implicated in improved drought resistance, disease tolerance, nitrogen uptake, and enhanced biological dinitrogen fixation. Currently, the potential consequences of large-scale release of AMF inoculants are not known, and it is assumed that AMF inoculation will be beneficial at best, or benign at worst. However, AMF species are known to differ in their ability to promote growth, ranging from mutualistic to parasitic, depending on host plant, and ambient climatic and soil conditions. Importantly, virtually all commercially available AMF inoculants contain the species Glomus intraradices. This species is preferred by the inoculant industry because it sporulates readily and is amenable to large-scale production. Does an AMF species that sporulates readily have the potential to displace other species that are inherently better growth promoters? Given the potential impact that a persistent, aggressively sporulating AMF species might have on beneficial indigenous AMF species and non-target host crops, we must be confident that the introduced species is indeed a desirable addition to the soil microbial community; that it is an effective growth promoter; that it will not displace naturally occurring AMF that are inherently better growth promoters; and there will be no negative consequences to non-target host crops grown in the future rotation. The objectives of this project are to: 1) assess the growth promotion characteristics (including synergies with rhizobial inoculants and dinitrogen fixation) of commercially available AMF inoculants as compared to indigenous AMF isolated from prairie soils; 2) assess the impact of AMF inoculation on populations and colonization success of indigenous AMF; 3) examine the impact of soil and climate/weather on the persistence of introduced AMF; and 4) examine the influence of AMF inoculant rate on growth promotion and competition with indigenous AMF.