PATTERNS OF RHIZOSPHERE MICROBIAL COMMUNITY STRUCTURE ASSOCIATED WITHCOOCCURRING PLANT-SPECIES

1 Rhizosphere populations of free-living bacteria and fungi associated with particular co-occurring plants were characterized to examine pat terns of microbial community structure in natural plant communities. S oil was collected from three co-occurring perennial plant pairs in an undisturbed field at Smoot Hill Biological Reserve, Pullman, Washingto n, USA, and from three different perennial plant pairs in an old-field community in Durham, North Carolina, USA. 2 Bacteria and fungi isolat ed from these rhizosphere soils were tested for their ability to utili ze various carbon substrates, their tolerance of antibiotics, and thei r sensitivity to osmotic and metal stresses. Multivariate analysis of physiological characteristics showed that rhizosphere microbial popula tions associated with particular plant pairs were significantly differ ent from one another. Plots of the first and second linear discriminat ive functions from a canonical analysis showed clustering of bacterial and fungal physiological characteristics according to plant pair. 3 R eplicates of particular plant pairs were planted into both greenhouse and field experiments to test whether bacterial community structure wa s influenced by different plant pairs. Repeated profile analyses showe d that initially similar rhizosphere bacterial communities differentia ted in both the greenhouse and field experiments and that these differ ences were associated with plant pairs. 4 The data suggest structure i n rhizosphere populations of free-living bacteria and fungi can be inf luenced by plants. They provide a first step in understanding the link between the structure and function of natural plant and microbial com munities.