Impact of growth stage on the bacterial community structure along maize roots, as determined by metabolic and genetic fingerprinting

Metabolic and genetic profiles were used to determine whether spatial and temporal variations in rhizodeposition along maize roots coincide with different bacterial community structures. Bacterial communities were extracted from the bulk soil and adhering soil of three maize rhizosphere zones (ramification, root hair-elongation, apex) 2 and 4 weeks after planting. Biolog((R)) substrate utilization profiles, and rDNA internal spacer analysis of bacterial communities, were compared. Biolog((R)) data showed that the functional abilities of bacterial communities from bulk and adhering soils were distinct after 2 weeks (Day 15). Moreover, these abilities were dissimilar between ramification zone on the one hand, and the root hair-elongation zone and apex on the other hand. The differences between bulk and rhizosphere soil responses were more pronounced after 4 weeks (Day 30), but rhizosphere samples were clearly aggregated. These results argue in favor of a greater influence of the maize rhizosphere environment on bacterial metabolic potentialities, mainly based on the developmental state of the plant. Different genetic fingerprints, and thus different genetic structures, were observed between bacterial communities at distinct sampling dates and, to a lesser extent, between rhizospheric and non-rhizospheric samples at both sampling dates. The latter difference was reinforced at Day 30. However, no clear groupings of samples could be identified on the basis of root-zone origin (ramification, root hair, apex). These results suggest a marked influence of time on microbial pools, irrespective of their root zone origins. (C) 2002 Elsevier Science B.V. All rights reserved.