Populations and functional diversity of bacteria associated with barley, wheat and canola roots

We investigated the effects of field pea (Pisum sativum)-based crop rotations on endophytic bacteria in roots and surrounding soil of cereal and oilseed crops. Barley (Hordeum vulgare), wheat (Triticum aestivum) and canola (Brassica rapa) were each grown (a) following peas inoculated with Rhizobium leguminosarum bv. viceae, (b) following uninoculated peas or (c) in monoculture. At flagleaf (cereal) or flowering (canola) growth stage, populations of soil-extract agar (SEA)-culturable bacteria ranged from log10 7.12 to log10 7.82 cells g-1 soil dry weight in the bulk soil, log10 7.15 to log10 8.12 cells g-1 soil in the rhizosphere, log10 7.77 to log10 10.39 cells g-1 root dry matter (DM) on the rhizoplane, and log10 5.56 to log10 7.63 cells g-1 root DM in root interiors (endophytic bacteria). Differences between treatments in populations and functional diversity of bacteria depended on where the bacteria were sampled in the continuum from bulk soil to root interiors. This affected correlations with crop N a...