Microbial diversity, structure and predicted carbon-cycling pathways show partial convergence in restored and natural salt marshes in Venice lagoon

Salt marshes are increasingly restored following widespread degradation, yet the responses of sediment microbial communities to restoration remain poorly understood, despite their central role in ecosystem functioning. We compared microbial diversity, composition, structure and predicted function between natural (N) and two types of restored salt marshes in Venice lagoon, Italy: marshes restored with tidal creeks (RC), favouring a more natural tidal exchange and creek formation at the low shore, and marshes restored with barriers (RB), which constrain tidal flow. We analysed sediment microbial communities in the three dominant habitat types of each marsh (unvegetated low shore, vegetated low shore, vegetated mid shore) by amplicon sequencing of the V4 and V5 hypervariable regions of the 16S rRNA gene. Microbial diversity was similar across natural and restored salt marshes, but microbial community structure and composition were different. Despite these taxonomic differences in microbial assemblages, predicted carbon-cycling pathways were broadly similar among restoration types, indicating potential functional convergence. In vegetated habitats, microbial community structure and composition differed between mid- and low-shore elevations in both restoration types, whereas richness and diversity did not. This pattern of taxonomic differentiation coupled with predicted functional similarity suggests that sediment microbial communities can rapidly re‑establish zonation and functional potential following restoration. Overall, our results show that restored salt marshes can support microbial communities with functional potential comparable to those of natural marshes, even when taxonomic composition differs and restoration designs vary. These findings are encouraging and highlight the importance of considering microbial functional potential when evaluating restoration success.