Salinity and nutrients shape soil microbial communities and functions in wetlands: Implications for conservation

Abstract

Soil microorganisms serve as pivotal drivers of biogeochemical processes and custodians of ecological equilibrium in wetland ecosystems. Understanding their functional potential across diverse types of wetlands is critical for informing targeted conservation initiatives and evidence-based restoration paradigms. Our metagenomic analysis revealed Proteobacteria and Ascomycota as the predominant bacterial and fungal phyla, respectively, across coastal, constructed, and swampy wetlands. Notably, microbial community exhibited significant distinctions in both taxonomic composition and functional gene β-diversity associated with carbon and sulfur cycles. Furthermore, the coastal wetland with high salinity exhibited elevated dissimilatory sulfate reduction potential but reduced soil organic carbon (SOC), assimilatory sulfate reduction, hemicellulose degradation, chitin degradation, cellulose degradation potential, and carbohydrate-active enzyme (CAZy) Shannon diversity compared with other wetlands. These results suggested microbial carbon degradation potential and SOC stocks decreased in high salinity habitat but improved in habitat with high available nitrogen and phosphorus, indicative of stress-adapted microbes. The constructed wetland displayed distinctive nitrogen transformation characteristics with higher nitrification, assimilatory nitrate reduction and lower methanogenesis potential compared with natural wetlands. Hierarchical partitioning analysis identified salinity and nitrate nitrogen (NO₃^--N) dominantly shaped the divergence of microbial community and functional genes associated with soil carbon, nitrogen, sulfur, and arsenic cycles. The genetic co-occurrence patterns of coastal wetland showed a high modularity and a low positive to negative connection ratio, indicating the high stability of microbial community. These findings illuminate the microbial metabolic versatility underpinning wetland biogeochemical cycle under environmental stress while providing critical implications for developing specific wetland conservation strategies.