Microbial community composition and functional diversity in the rhizosphere of maize

This study investigates the small-scale stratification of bacterial community composition and functional diversity in the rhizosphere of maize. Maize seedlings were grown in a microcosm with a horizontal mesh (53 muM) creating a planar root mat and rhizosphere soil. An unplanted microcosm served as control. Thin slices of soil were cut at different distances from the mesh surface (0.2-5.0 mm) and analysed for bacterial community composition by PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) of 16S rDNA and tested for activities of different enzymes involved in C, N, P and S cycling. Bacterial community composition and microbial functional diversity were affected by the presence of the maize roots. The bacterial composition showed a clear gradient up to 2.2 mm from the root surface, while no such gradient was observed in the unplanted pot. Invertase and phosphatase activities were higher in the close vicinity of maize roots (0.2-0.8 mm), whereas xylanase activity was unaffected. This study shows that the changes in bacterial community composition and functional diversity induced by roots may extend several millimetres into the soil.