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Small molecules rule the rhizosphere. This has been clear since the first definition of the rhizosphere in 1904, but it emerged much later that microorganisms are central to the dynamic conversation that creates the metabolic profile of the rhizosphere. Although plants initiate the conversation by pumping photosynthate from their roots, microorganisms rapidly respond by modifying plant chemistry and contributing metabolites of their own. Roles of certain microorganisms and metabolites have been elucidated, but a comprehensive portrait of the microbial membership, chemical composition, and dynamic responses of the rhizosphere has eluded us. Recent technical advances provide a new opportunity to tackle the complexity of the rhizosphere. Analysis of 16S rRNA gene sequences provides a census of both culturable and as-yet-uncultured bacteria in the rhizosphere community. Metagenomic sequence analysis offers insight into the genetic potential of the community, and functional metagenomics provides an activity-based approach to discovering new genes from uncultured organisms through functional expression in surrogate hosts. New methodology for mass spectrometry now promises a complete metabolomic portrait of the rhizosphere in real time. These methods used in concert have the potential to reveal new dimensions of the rhizosphere, particularly its variation over space and time and responses to microbial perturbation.<p><p>Keywords: