Exploring local and regional drivers of microbial biodiversity across freshwater ponds

Aim Ponds are isolated, highly variable environments that exhibit low spatial autocorrelation of environmental variables and have island-like features, which may give rise to unique biogeographic patterns compared to terrestrial and lotic environments. Here, we evaluate whether commonly observed biogeographical patterns apply to microbial biodiversity in pond fungal and bacterial communities. Specifically, we tested (1) whether these communities follow latitudinal diversity gradients and distance decay relationships, and (2) if variation in community composition or richness was related to specific environmental or land-use factors. Location Eastern, USA Time period Summer, 2022 Taxa Bacteria and Fungi Methods We collected water and muck from 39 ponds across 8 states in the Eastern USA. We extracted DNA from these samples and sequenced sections of the 16S rRNA and ITS1 genes to survey the bacterial and fungal communities, before evaluating biogeographical patterns. Results We found evidence of latitudinal diversity gradients in muck fungal communities, but not bacterial communities. We observed weak distance decay relationships in all sample types. Community richness was related to some environmental filters, where conductivity was positively related to water bacterial richness, but negatively related to muck fungal richness. Environmental drivers explained low to moderate variation in microbial composition, with temperature universally linked to microbial biodiversity. Conclusions Pond microbiomes exhibit unique biogeographic patterns depending on the microhabitat and microbial taxa in question, with land use and abiotic conditions, especially temperature, explaining some variation in microbial biodiversity across sites. Our findings suggest that the low spatial autocorrelation in environmental conditions and the lack of connectivity across ponds provides a useful framework for investigating localized drivers of microbial diversity.