Rhizosphere microbial communities of canola and wheat at six paired field sites

Authors: Hansen, Jeremy; SCHILLINGER, WILLIAM - Washington State University; SULLIVAN, TARAH - Washington State University; Paulitz, Timothy

Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2018
Publication Date: 9/7/2018
Citation: Hansen, J.C., Schillinger, W., Sullivan, T., Paulitz, T.C. 2018. Rhizosphere microbial communities of canola and wheat at six paired field sites. Applied Soil Ecology. 130:185-193. https://doi.org/10.1016/j.apsoil.2018.06.012.
DOI: https://doi.org/10.1016/j.apsoil.2018.06.012

Interpretive Summary: A study conducted in eastern Washington reported reduced yields of wheat when planted after a canola crop. We investigated the effect of canola on rhizosphere soil microbiology to determine if canola created changes in the soil microbial community that could impact subsequent crop yields. Canola plants contain compounds that can reduce soil pathogens, but can also reduce beneficial soil organisms and thereby crop productivity. We found that major portions of the rhizosphere microbial community were impacted by the close association with canola roots compared to wheat. The results reported here introduce the potential for negative rotational effects of canola and supplement the current literature which has largely reported increased yields in wheat following canola. Findings of this study will enable regional farmers to adjust their sequence of planting canola in wheat-based rotations that allow for continued crop diversification and to maintain optimum crop yield potential.

Technical Abstract: Plant physical and chemical characteristics are known to alter rhizosphere microbial communities, but the effect of introducing canola (Brassica napus L.) into monoculture wheat (Triticum aestivum L.) rotations is not clear. Results from a field study in eastern Washington showed that winter canola (WC) influenced the bulk soil microbial community and differentiated it from the community associated with winter wheat (WW). Abundance of soil fungi, including mycorrhizae, was reduced with the introduction of WC. The objective of this research was to determine the differences and similarities in the rhizosphere microbial communities of WC and WW. Canola and wheat rhizosphere soil was collected from six dryland farms in Adams and Douglas Counties, WA. Each farm was a paired site with WC and WW grown in adjacent fields of the same soil type, landscape orientation, and crop history. Canola, or any non-cereal crop, had never been grown previously at the experimental sites. Microbial biomass and community composition, determined using phospholipid fatty acid analysis (PLFA), revealed differences that were primarily associated with landscape position at the initial fall sampling. Data from spring samples, however, showed significant differences in microbial communities between WC and WW rhizosphere soils. Data suggest that initial (fall) microbial community composition were an artifact of previous histories of monocrop wheat production and varied with expected differences in landscape position. As the crops developed, microbial communities became more dissimilar and were discriminated by crop species. Our results show that WC can have significant effects on rhizosphere microbial biomass and community structure in wheat-based cropping systems. Changes in microbial abundance and community structure can affect microbially-mediated soil processes, and potentially the performance of subsequent crops.