Soil bacterial community succession during long-term ecosystem development

The physicochemical and biological gradients of soil and vegetative succession along the Franz Josef chronosequence in New Zealand were used to test whether bacterial communities show patterns of change associated with long-term ecosystem development. Pyrosequencing was conducted on soil-derived 16S rRNA genes at nine stages of ecosystem progression and retrogression, ranging in age from 60 to c. 120000years since glacial retreat. Bray-Curtis ordination indicated that the bacterial communities showed clear patterns of change that were closely aligned with ecosystem development, pedogenesis and vegetative succession (Mantel test; r=0.58; P<0.001). Eighty per cent (80%) of the explained variability in bacterial community structure was observed during the first c. 1000years of development, when bacterial richness (Simpson's 1/D) declined from 130 to 30. The relatively high turnover of soil bacterial communities corresponded with an integrative plant-microbial successional feedback' model that predicts primarily negative feedbacks between plants and soil bacterial communities during progression and early pedogenesis. Positive feedbacks, similar to those of the plant community, could explain the long periods of community stability during later retrogressive stages of ecosystem development. This hypothesized model provides a consistent description linking belowground communities to ecosystem development and succession. The research, using deep sequencing technology, provides the first evidence for soil bacterial community change associated with the process of long-term ecosystem development. How these bacterial community changes are linked to the processes of primary ecosystem succession is not known and needs further investigation.