ABSTRACTSeagrass colonization changes the chemistry and biogeochemical cycles mediated by microbes in coastal sediments. In this study, we molecularly characterized the diazotrophic assemblages and entire bacterial community in surface sediments of aZostera marina-colonized coastal lagoon in northern China. Higher nitrogenase gene (nifH) copy numbers were detected in the sediments from the vegetated region than in the sediments from the unvegetated region nearby. ThenifHphylotypes detected were mostly affiliated with theGeobacteraceae,Desulfobulbus,Desulfocapsa, andPseudomonas. Redundancy analysis based on terminal restriction fragment length polymorphism analysis showed that the distribution ofnifHgenotypes was mostly shaped by the ratio of total organic carbon to total organic nitrogen, the concentration of cadmium in the sediments, and the pH of the overlying water. High-throughput sequencing and phylogenetic analyses of bacterial 16S rRNA genes also indicated the presence ofGeobacteraceaeandDesulfobulbaceaephylotypes in these samples. A comparison of these results with those of previous studies suggests the prevalence and predominance of iron(III)-reducingGeobacteraceaeand sulfate-reducingDesulfobulbaceaediazotrophs in coastal sedimentary environments. Although the entire bacterial community structure was not significantly different between these two niches,Desulfococcus(Deltaproteobacteria) andAnaerolineae(Chloroflexi) presented with much higher proportions in the vegetated sediments, andFlavobacteriaceae(Bacteroidetes) occurred more frequently in the bare sediments. These data suggest that the high bioavailability of organic matter (indicated by relatively lower carbon-to-nitrogen ratios) and the less-reducing anaerobic condition in vegetated sediments may favorDesulfococcusandAnaerolineaelineages, which are potentially important populations in benthic carbon and sulfur cycling in the highly productive seagrass ecosystem.
Seagrass (Zostera marina) promotes nitrification potential and selects specific ammonia oxidizers in coastal sediments
