Consistent spatial distribution patterns of bacterial communities revealed by serial time-archived soils from long-term field experiments

Many precious air-dried soil samples are currently stored by institutions across the world, and they have been proved useful in retrieving historical information of soil microbial ecology, such as the shifts of microbial populations and the effects of agricultural managements on soil microbial communities. However, most of those retrospective studies on microorganisms in archived soils were mainly conducted through PCR-DGGE or T-RFLP analysis, which was less sensitive to low-abundance species. In order to assess whether archived soils could reveal the spatial distribution of microbial communities at large spatial scale, especially the rare microbial taxa, a total of 117 serial time-historical samples from eight long-term field experimental stations of the Chinese Ecosystem Research Network were analyzed using high-throughput sequencing. The non-metric multidimensional scaling (NMDS) analyses showed that both the total bacterial communities and the rare bacterial subcommunities were distinctly clustered into different groups corresponding to each experimental station, and that analogous distribution patterns of bacterial communities existed between each two sampling years for both the total and the rare taxa, though the microbial community composition changed over time. The corresponding hierarchical clustering analyses demonstrated that soil bacterial communities for both the total and the rare taxa could be clustered into five groups for all samples and for the sub-samples of each sampling year, which corresponded to five eco-geographic regions in the Eco-Geographic Regional System of China. The results from this investigation highlighted the great value of serial time-archived soils in revealing the spatial distribution patterns of bacterial communities for both the total and the rare taxa at large spatial scale.