Work

Night and day in the Salt Marshes: Sediment Microbial Communities Remain Stable Over a Summer Diel Cycle

Year: 2026

Type: article

Abstract: Salt marshes are crucial habitats for carbon sequestration and provide many valuable ecosystem services to humankind, such as water quality regulation and coastal protection. Despite this, they are globally threatened by anthropogenic pressures, and restoration efforts are increasingly needed. Within salt marshes, microbial communities play a central role in key biogeochemical processes underlying many ecosystem services provided by these habitats, but their short-term temporal dynamics under strong physicochemical fluctuations – typical of intertidal productive ecosystems – remain poorly understood. In this study, the microbial communities in the sediments of two salt marshes in the Venice Lagoon, a productive microtidal coastal ecosystem, were characterised at four moments of a single summer diel cycle: sunset, night, dawn and solar noon. Prokaryotes and eukaryotes were characterised using 16 S and 18 S rRNA genes metabarcoding, respectively, and the functional potential of prokaryotes was explored using metagenomics. The measurements of physicochemical parameters revealed pronounced diel oscillations in temperature and dissolved oxygen. Under these conditions, prokaryotic and eukaryotic communities showed minor shifts in taxonomic composition during the sampled diel cycle. Metagenomes revealed functionally redundant and metabolically versatile communities, dominated by taxa involved in organic-matter degradation, sulphur cycling, denitrification and sulphur-oxidising chemolithoautotrophic carbon fixation. Overall, these results suggest that, over the diel timescale investigated, salt marsh sediments host functionally robust communities adapted to strong short-term fluctuations in physicochemical conditions. Modulating their activities, rather than compositional restructuring, may allow these communities to sustain key ecological processes relevant to carbon and nutrient cycling.

Source: Microbial Ecology

DOI: 10.1007/s00248-026-02890-4