The microbial community composition and potential for carbon sequestration differences among mudflats with and without biofilm colonization.

Mudflats play an important role in coastal carbon cycling. The colonization of diatom-dominated microphytobenthic biofilms and associated heterotrophic microbial communities, affects the biogeochemical cycling in mudflats. Yet, the influence of biofilm colonization on the microbial communities and organic matter profiles in mudflats remains poorly understood. Here, 84 samples were collected in different seasons, locations and depths with/without biofilms in tidal flats of Zhejiang, China, and a multiparametric analysis was performed on environmental factors, microbial communities and dissolved organic matter (DOM) profiles to reveal the multidimensional influence of biofilm colonization on mudflats. The results showed that, compared with surface adjacent bare sediment (surface ABS), biofilms exhibited higher carbon stocks, lower bacterial diversity, and a shift in the dominant community assembly process from dispersal limitation to homogeneous dispersal. The microbial communities in biofilms and related sediments showed a higher abundance of functional genes involved in carbon, nitrogen and sulfur cycling, including carbon fixation and metabolism, leading to high proportion of recalcitrant DOM in the biofilm-related sediments, in which, Pseudomonadota, Bacteroidota, Chloroflexota and Bacillota acted as key functional groups. This study highlights the association between biofilm occurrence, microbial community composition, functional potential, and organic matter characteristics in mudflat sediments, highlighting the potential contribution of biofilms to carbon retention and transformation processes in mudflat ecosystems.