Variation of Microbial Communities in Soil, Rhizosphere, and Rhizoplane in Response to Crop Species, Soil Type, and Crop Development

Abstract

We investigated the influence of plant species, soil type, and plant development time on the shaping of microbial communities in soil and in association with roots. The sample group consisted of a total of 32 microcosms in three habitats: soil, rhizosphere, and rhizoplane. Communities were represented by the patterns of a sequence-specific separation of rRNA target sequences. Effects of experimental parameters were classified by a cluster analysis of pattern similarities. The type of plant species (clover, bean, or alfalfa) had the greatest effect in plant-associated habitats and also affected soil patterns. Plant development had a minor habitatdependent effect that was partly obscured by replicate variation. The results stress the applicability of biased community representations in an analysis of induced variation.A great variety of abiotic and biotic factors shape soil-and plant-associated habitats and modify the compositions and activities of their microbial communities, which in turn bear upon the quality of their environment, the growth of plants, and the production of root exudates (2). Bacterial communities in rootassociated habitats respond with respect to density, composition, and activity to the abundance and great diversity of organic root exudates, eventually yielding plant species-specific microfloras which may also vary during plant development stages (3,4,17,18). Due in part to the scarcity of convenient methods for exploration, our understanding of the different degrees and dynamics of microbial community variation as induced by soil type, plant type, or plant development is limited so far (5, 18).As one step towards a better understanding of the relative variations of complex microbial communities in response to common conditions of agricultural practice, we studied the effects of plant type, soil type, and temporal development on the compositions and activities of microbial communities in soil and in association with leguminous plants. Therefore, we compared banding patterns of amplified 16S rRNA target sequences from soil, rhizosphere, and rhizoplane fractions by temperature gradient gel electrophoresis (TGGE). This technique offers a culture-independent method for tracking dominant bacterial populations in space and time (21). Unlike with the use of 16S ribosomal DNA target sequences for such investigations, the use of rRNA modifies the observation in favor of metabolically active microorganisms, because the abundance of ribosomes in a community can be viewed as a speciesdependent function of cell numbers and their growth rates (9,24,28,31). To the best of our knowledge, this study represents the first approach using culture-independent methods to systematically monitor the degree of variation of active, dominant bacterial populations in response to soil type, plant type, and the state of development of the plant.In detail, soil samples from two different agricultural field sites in Braunschweig, Lower Saxony, Germany, were used: BBA soil (loamy sand) and FAL soil (para brown earth, silty sa...

Changes in land use alter the structure of bacterial communities in Western Amazon soils

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Despite strong seasonal responses, soil microbial consortia are more resilient to long-term changes in rainfall than overlying grassland

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Soil Fungistasis Against Fusarium Graminearum Under Different Crop Management Systems

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