The distribution of microbial diversity is driven by factors influencing dispersal across space and persistence through time. Dormancy is a general microbial life history trait that influences both spatial and temporal dynamics of microbial diversity. Microbial dormancy leads to the emergence of seed banks that allow microbes to persist under adverse conditions, and is widely believed to dampen dispersal limitation. We tested predictions for the influence of microbial seed banks on geographic and environmental distance-decay relationships (DDR) of bacterial communities from across 49 ponds that were constructed for conservation purposes. DDR’s are primary biogeographic patterns that reveal the influence of spatial and environmental autocorrelation on the compositional similarity of ecological communities. We characterized microbial communities by sequencing the 16S rRNA genes and transcripts to describe the entire microbial community and the metabolically active fraction, respectively. We measured 19 environmental and geographic variables associated with each pond.
We found no evidence of spatial autocorrelation among environmental variables, allowing us to examine environmental and geographic DDRs independently. Similar environments had greater similarity in microbial community composition than dissimilar environments. This pattern was stronger for the active fraction than for the entire community. Environmental DDRs for the active fraction had slopes and y-intercepts that were nearly twice as great as DDRs for the entire community, revealing a strong influence of the local environment on shaping the composition of the active community. In contrast, we observed almost no geographic pattern in microbial community similarity. These findings point to two general effects of dormancy on microbial biogeography. Specifically, the historical legacy of the local seed bank and the randomizing influence of widespread dispersal appear to shape the spatial diversity of microbial communities across discrete habitats at regional spatial scales.