Inter-Kingdom Networks of Canola Microbiome Reveal Bradyrhizobium as Keystone Species and Underline the Importance of Bulk Soil in Microbial Studies to Enhance Canola Production

Long-Term Persistence of Arbuscular Mycorrhizal Fungi in the Rhizosphere and Bulk Soils of Non-host Brassica napus and Their Networks of Co-occurring Microbes

“…Two sites were in Alberta in the sub-humid brown soil zone: one site in Lacombe (latitude 52.5 • N, longitude 113.7 • W) and the other site in Lethbridge (latitude 49.7 • N, longitude 112.8 • W) and a third site was in Swift Current Saskatchewan, in the semi-arid brown soil zone (latitude 50.3 • N, longitude 107.7 • W). The fourth site (Melfort), used in the study by Floc'h et al (2021), was discarded. Crops were grown according to best management practices, as described in a study by Harker et al (2015).…”

“…However, axenic AMF growth is known to be stimulated in vitro by coculture with plant growth-promoting bacteria (Abdellatif et al, 2019). Thus, the report of Floc'h et al (2021) motivated the verification of this hypothesis: We expect that canola negatively impacts the AMF community in function of its frequency in crop rotations. Furthermore, by using network analysis, we will explore the potential interactions that AMF develop with other microbes, such as fungi and bacteria, in the canola rhizosphere and bulk soil.…”

“…As we wanted to know with what microbes AMF could potentially interact with, we used the exact same samples from a study by Floc'h et al (2021), in which we reused the ITS and 16S ASV tables of this study in our analysis. The protocols of DNA extraction and amplification, sequencing, and bioinformatic processing of ITS and 16S sequences are described in a study by Floc'h et al (2021).…”

“…Among others, glucosinolates and isocyanates are toxic, which may explain the non-host plant status of canola. But, from an analysis of canola-associated soil fungi based on fungal internal transcribed spacer (ITS), Floc'h et al (2021) reported the presence of AMF from the Glomeraceae family in the rhizosphere and bulk soil samples from fields that were in canola monoculture for 10 years. The AMF depend on a host for their carbon needs (Rich et al, 2017) and the persistence of AMF for such a long period of time in absence of mycotrophic host plants is unexpected.…”

“…In this study, we used a long-term assay held by Agriculture and Agri-Food Canada in three locations of the Canadian Prairies to identify the AMF living in canola rhizosphere and bulk soil and the samples we used are those of Floc'h et al (2021) from which we extracted and amplified the 18S region of AMF ribosomal DNA (rDNA) to only target AMF. We used network analysis to explore the possible interactions of these AMF with the fungi and bacteria also residing in the canola rhizosphere and bulk soil.…”