Spatial differences in bacterial communities preserved in soils archived for a decade

The spatial differences in microbial communities have been widely investigated in many environments through culture-independent molecular biological methods. Currently, for archived soils, there is a concern whether the spatial differences are still preserved in them after long-term storage. Considering plenty of archived soils being stored by institutions, we tried to explore whether they could provide certain information about microbial biogeography. In the present study, high-throughput sequencing of the 16S rRNA gene was conducted for archived soil samples, which were collected in different years from four agricultural long-term experimental stations of the Chinese Ecosystem Research Network and had been stored for approximate 1, 6 and 11 years. After processing the raw high-throughput sequencing data, a total of 10,623 OTUs belonging to 46 phyla were detected across all 72 soil samples. The results of OTU analysis showed that the overlap ratio (> 57.35%) of bacterial OTUs between sampling years at the same station was higher than that (< 32.39%) between experimental stations in the same year. Simultaneously, the differences in taxonomic counts among stations in the same sampling year overwhelmed those among sampling years at the same station, and a similar result was observed for bacterial alpha-diversity as well. More importantly, soil bacterial communities were distinctly different among geographic locations (ANOSIM R = 0.997 and p < 0.001), while differed far less among sampling years (R = 0.085, p = 0.005). Altogether, the results from this investigation demonstrated that soils archived for about a decade were still applicable in revealing spatial differences in soil bacterial communities, and these differences were hardly obscured by storage time, suggesting the potential of archived soils in studies on microbial geography.