Community assembly of comammox in coastal wetlands across southeastern China.

Complete ammonia oxidizers (comammox ) are ubiquitous in coastal wetland sediments and play an important role in nitrification. Our study examined the impact of habitat modifications on comammox communities in coastal wetland sediments across tropical and subtropical regions of southeastern China. Samples were collected from 21 coastal wetlands in five provinces where native mudflats were invaded by and subsequently converted to aquaculture ponds. The results showed that comammox abundances were mainly influenced by sediment grain size rather than by habitat modifications. Compared to marshes and native mudflats, aquaculture pond sediments had lower comammox diversity, lower clade A.1 abundance, and higher clade A.2 abundance. Sulfate concentration was the most important factor controlling the diversity of comammox . The response of comammox community to habitat change varied significantly by location, and environmental variables accounted for only 11.2% of the variations in community structure across all sites. In all three habitat types, dispersal limitation largely controlled the comammox community assembly process, indicating the stochastic nature of these sediment communities in coastal wetlands. IMPORTANCE Comammox have recently gained attention for their potential role in nitrification and nitrous oxide (NO) emissions in soil and sediment. However, their distribution and assembly in impacted coastal wetland are poorly understood, particularly on a large spatial scale. Our study provides novel evidence that the effects of habitat modification on comammox communities are dependent on the location of the wetland. We also found that the assembly of comammox communities in coastal wetlands was mainly governed by stochastic processes. Nevertheless, sediment grain size and sulfate concentration were identified as key variables affecting comammox abundance and diversity in coastal sediments. These findings are significant as they advance our understanding of the environmental adaptation of comammox and how future landscape modifications may impact their abundance and diversity in coastal wetlands.