Characterizing spatiotemporal differences in microbial communities of flocculent organic matter in Everglades marshes

Flocculent organic matter (floc) is unconsolidated matter made up of detritus and microbes, which are important regulators of ecosystem functioning. The composition and diversity of microbial communities of floc in subtropical wetlands likely influenced biogeochemical cycles. How floc-specific microbial communities vary spatiotemporally with and respond to changes in seasonal water depth may help us to better predict larger ecosystem properties. We collected quarterly benthic floc samples from shallower, shorter-hydroperiod, marl-dominated marshes and deeper, longer-hydroperiod, peat-dominated marshes in Everglades National Park (Florida, USA). We quantified the taxonomic groups of floc-specific Bacteria, Archaea, and Eukaryota during wet (May-November) and dry seasons (December-April). We examined relationships between floc microbial community composition and floc-specific metabolism, bulk density, and carbon and nutrient concentrations, as well as abiotic conditions (water depth and benthic photosynthetically active radiation, PAR). The most abundant taxonomic groups were Proteobacteria, Euryarchaeota and Metazoa Animalia (a substantive detrital component of floc). Microbial community structure was influenced by water depth, benthic PAR, floc-specific biogeochemistry and metabolism. Bacterial and archaeal community structures varied more seasonally rather than spatially, whereas eukaryotic community structure varied more spatially than seasonally. Our results indicate that changes in water depth that increased floc-specific carbon and nutrient concentrations, and microbial respiration rates, which were influenced by changes in water depth, were associated with differences in floc-specific microbial communities. Given the widespread occurrence of floc and its high capacity to be mobilized by seasonal hydrology, understanding the composition and biogeochemical function of floc-derived microbes has implications for carbon storage in wetland ecosystems.