Patterns of rhizosphere microbial community structure associated with co-occurring plant species

1 Rhizosphere populations of free-living bacteria and fungi associated with particular co-occurring plants were characterized to examine patterns of microbial community structure in natural plant communities. Soil was collected from three co-occurring perennial plant pairs in an undisturbed field at Smoot Hill Biological Reserve, Pullman, Washington, USA, and from three different perennial plant pairs in an old-field community in Durham, North Carolina, USA. 2 Bacteria and fungi isolated from these rhizosphere soils were tested for their ability to utilize various carbon substrates, their tolerance of antibiotics, and their sensitivity to osmotic and metal stresses. Multivariate analysis of physiological characteristics showed that rhizosphere microbial populations associated with particular plant pairs were significantly different from one another. Plots of the first and second linear discriminative functions from a canonical analysis showed clustering of bacterial and fungal physiological characteristics according to plant pair. 3 Replicates of particular plant pairs were planted into both greenhouse and field experiments to test whether bacterial community structure was influenced by different plant pairs. Repeated profile analyses showed that initially similar rhizosphere bacterial communities differentiated in both the greenhouse and field experiments and that these differences were associated with plant pairs. 4 The data suggest structure in rhizosphere populations of free-living bacteria and fungi can be influenced by plants. They provide a first step in understanding the link between the structure and function of natural plant and microbial communities.