Bacterial community structure in the rhizosphere is influenced by carbon exudation from roots - carbon availability limits microbial growth in soil.  Bacterial numbers and diversity are thought to be directly proportional to the quantity and diversity of carbon-containing compounds released by roots; thus communities should reveal the sites of C-release with which they are most closely associated.  To investigate bacterial community structure on a scale that is relevant to the sphere of influence of different physiological zones along the root, we are developing micro-sampling techniques.  Microbial populations appear to be higher on the basal regions of young roots than in the root cap or elongation zones, possibly reflecting the lag between colonisation of the root and bacterial proliferation.  (Paul Dennis, PhD CASE student with the Natural History Museum and University College, jointly with Tony Miller, PSC and Penny Hirsch)

Location of lux-marked P. fluorescens on B. napus root

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