Bacterial Community Succession During Soil and Ecosystem Development.

Organism succession during ecosystem development has been relatively well studied for aboveground macro-bial communities but only a few attempts have been made to understand whether soil microbial communities will follow a pattern of succession in their underground ecosystems. Studying the composition and diversity of microbial communities during soil and ecosystem development will thus provide insight into the role that various geochemical and biotic gradients play in microbial community genesis. The study site was situated along the eastern shore Lake Michigan. Soils were sampled from the A-horizon (~0 to 7cm depth) of 9 replicated dune ridges with depositional ages ranging from 95 to ~4200 years. Recently deposited beach sands were also sampled. There were thus 10 soil treatments and 5 replicate sampling locations along each ridge. Bacterial tag-encoded FLX amplicon pyrosequencing of the 16S rRNA gene produced approximately 2,000 sequences from each replicate dune ridge. Soil nutrient cations, pH and other chemical soil characteristics change dramatically during the first few hundred years of development and reflect changes in aboveground primary succession. For example, beach grass and shrubs in the younger dunes were replaced by conifers around 200-400 years of succession. This dynamic mirrored that of pH along the chronosequence. Preliminary results from two other recently sampled chronosequences indicate that bacterial communities show strong patterns of development associated with soil and ecosystem change. The Michigan chronosequence is somewhat unique in that vegetation continues to change during later stages of soil development and will allow us to assess whether vegetation or soil characteristics more closely correlate with bacterial community change. These data and insights into the relative importance of plant and soil effects on microbial community assembly will be presented.