Stable Soil Bacterial Communities and Ecosystem Development: Are Small Differences Between Global Hemispheres a Big Deal?.

Biogeographical and bacterial community change during vegetative and ecosystem succession were studied in several locations in the Southern and Northern Hemispheres. In Michigan and Georgia, and in central and southern coasts of New Zealand, 4 chronosequences were studied. Each location included 4 to 5 replicate sites represented by 5 to 9 different stages (ages) of soil development.  The bacterial composition and diversity in the soil was studied using bacterial tag-encoded FLX amplicon pyrosequencing of the 16S rRNA gene. As hypothesized, Bray-Curtis ordination indicated that bacterial community assembly changed very quickly along the developmental gradient and then stabilized generally after only several hundred years of soil development. , however, each ecosystem showed similar change through soil development that were related to levels of Ca, Mg and pH (r ~ 0.83, 0.84 and 0.81).  Bacterial diversity represented by Simpson’s reciprocal index (Simpson’s 1/D) showed a steady decline from youngest to the oldest sites (212 to 58). All 4 ecosystems showed similar patterns of bacterial and vegetative change. Though small compared to the variability associated with ecosystem development, differences between the hemispheres were also observed. Whether these differences are intrinsic properties of the ecosystems, such as the endemic vegetation found in New Zealand or a result of pedogenesis remain to be answered. Following early ecosystem development, community change was resiliant to change, suggesting that bacterial communities are relatively stable over long-periods of soil and ecosystem development.