SummaryLittle is known about the relative influence of historic processes and environmental gradients on shaping the diversity of single-celled eukaryotes in marine benthos. By combining pyrosequencing of 18S ribosomal RNA genes with data on multiple environmental factors, we investigated the diversity of microeukaryotes in surficial sediments of three basins of the Yellow Sea Large Marine Ecosystem. A considerable proportion (about 20%) of reads was affiliated with known parasitoid protists. Dinophyta and Ciliophora appeared dominant in terms of relative proportion of reads and operational taxonomic unit (OTU) richness. Overall, OTU richness of benthic microeukaryotes decreased with increasing water depth and decreasing pH. While community composition was significantly different among basins, partial Mantel tests indicated a depth-decay pattern of community similarity, whereby water depth, rather than geographic distance or environment, shaped β-diversity of benthic microeukaryotes (including both the abundant and the rare biosphere) on a regional scale. Similar hydrographic and mineralogical factors contributed to the biogeography of both the abundant and the rare OTUs. The trace metal vanadium had a significant effect on the biogeography of the rare biosphere. Our study sheds new light on the composition, diversity patterns and underlying mechanisms of single-celled eukaryote distribution in surficial sediments of coastal oceans.

dSeagrass 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 a Zostera 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. The nifH phylotypes detected were mostly affiliated with the Geobacteraceae, Desulfobulbus, Desulfocapsa, and Pseudomonas. Redundancy analysis based on terminal restriction fragment length polymorphism analysis showed that the distribution of nifH genotypes 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 of Geobacteraceae and Desulfobulbaceae phylotypes in these samples. A comparison of these results with those of previous studies suggests the prevalence and predominance of iron(III)-reducing Geobacteraceae and sulfate-reducing Desulfobulbaceae diazotrophs in coastal sedimentary environments. Although the entire bacterial community structure was not significantly different between these two niches, Desulfococcus (Deltaproteobacteria) and Anaerolineae (Chloroflexi) presented with much higher proportions in the vegetated sediments, and Flavobacteriaceae (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 favor Desulfococcus and Anaerolineae lineages, which are potentially important populations in benthic carbon and sulfur cycling in the highly productive seagrass ecosystem. Sediments colonized by seagrass in shallow estuarine and coastal environments are hot spots of microbial activities. Seagrass meadows enrich the sediment carbon matter by exuding dissolved organic carbon (DOC) through their roots and trapping organic particles from the overlying water (1). Due to the effects of seagrass on nutrient deposition, retention, and mineralization from organic matter, the nutrients in pore water are often richer in seagrass sediments than in sediments from unvegetated regions (1-3). Seagrass roots also release photosynthesis-produced O 2 into sediments, which results in less-reducing conditions in seagrass meadows than unvegetated sediments and contributes to the prevention of the accumulation of sulfides, the toxic products of sulfate reduction in anaerobic sedimentary environments that could play a role in dieback events in seagrass meadows (1, 4). Higher bacterial populations and activities (particularly bacterium-mediated sulfate reduction) are usually found in seagrass-vegetated sites and not in unvegetated sediments (5-8).Because the gro...

14Sesbania cannabina is a plant that grows naturally along the seashores in Rudong 15County, China (RDC) and it has been introduced into the Yellow River Delta (YRD) 16 as a pioneer plant to improve the saline-alkaline soils. In order to investigate the 17 diversity of S. cannabina rhizobia in these soils, a total of 198 rhizobial isolates were