Shifts of Sediment Microbial Community Structure along a Salinized and Degraded River Continuum

Succession of sediment microbial community along salinized and degraded river continuums where discharge declines and nutrient loading increases has received little attention. This issue was studied in a 120-km sediment continuum from upstream to estuary of the Jiyun River, northern China. Microbial community was investigated by phospholipid fatty acid (PLFA) analysis and 16S ribosomal ribonucleic acid (rRNA) gene sequencing. Microbial PLFA contents varied from 1.48 to 7.64 nmol g(-1). Salinity decreased microbial, bacterial, and actinomycetic PLFA contents (p < 0.05), but had little effect on fungal PLFA contents. Dissolved organic carbon and dissolved nitrogen increased microbial, bacterial, and actinomycetic PLFAs (p < 0.05), but did not affect fungal PLFAs. Fungal PLFAs were mainly associated with the contents of sediment organic carbon (SOC) and total nitrogen (TN). Salinity decreased the ratio of Gram-positive/Gram-negative PLFAs but not the ratio of fungal/bacterial PLFAs. Bacterial communities were dominated by Proteobacteria, Firmicutes, and Bacteroidetes phyla. PLFA analysis and 16S rRNA sequencing returned similar results with respect to the change in bacterial community composition. Shannon-Wiener indices of bacterial operational taxonomic units were negatively correlated with SOC and TN. In conclusion, salinity and nutrients are collectively regulating the shifts in sediment microbial community structure along the river continuum.