Microbial Community In Surface Sediments From The Western Arctic Ocean And Its Implications For Silicate Pump

Surface sediment samples were collected from 26 stations of the Western Arctic Ocean.Diversity and community structure of microeukaryotes and microprokaryotes were assessed by Illumina high-throughput sequencing of 18 S r DNA V4 region and16 S r DNA V4-V5 regions,respectively.The interspecific relationships among microeukaryotes and microprokaryotes were revealed by molecular ecological network.Biogenic elements including total organic carbon(TOC),bio-silicon(BSi),total nitrogen(TN),total phosphorus(TP),were analyzed in the sediment samples.The origin of organic matter and structure of biological carbon pump were assessed by the molar ratios of biogenic elements.Contributions of microbial community to biological carbon pump were evaluated based on the relationships between biogenic elements and microeukaryotes and microprokaryotes.The results of this study reveal the diversity and structure of microbial community in the surface sediments from the Western Arctic Ocean and the implications of microbial community to silicate pump,give a better understanding on the background of marine environments,and thus provide a scientific basis for the protection of the Western Arctic Ocean ecosystem and strategies for the global changing crisis.The main results of this study are as follows:(1)A total of 750,045 DNA reads and 618 OTUs of microeukaryotes were obtained by high-throughput sequencing.Eukaryotic algae dominated in DNA reads,which accounted for 63.96% of the total sequences.And protozoa dominated in OTU richness,which accounted for 60.52% of the total OTUs.There were 23 species,33 genus,17 classes in 5 phyla detected in eukaryotic algae,23 species,46 genus,27 classes in 12 phyla in protozoa,and 5 species,8 genus,7 classes in 5 phyla of fungi.The ice algae Chaetoceros socialis was the most dominated species in microeukaryotes with relative reads of 57.45% to the microeukaryotes.Other ice algae including Polarella glacialis,Micromonas Polaris and Chaetoceros Diadema were also important dominant species.In addition,a small number of warm temperate species and freshwater species were detected.The sums of abundant and rare OTUs of microeukaryotes were 55 OTUs and 185 OTUs respectively.In molecular ecological network of microeukaryotes,the proportion of positive correlation was 83.25%,suggesting cooperative or symbiotic relationships between species.Furthermore,as the central nodes of the network,Thecofilosea,Phytomyxea,Imbricatea,Labyrinthulea,and Mediophyceae played significant roles in microeukaryotes in the surface sediments from the Western Arctic Ocean.(2)A total of 1,999,348 DNA reads and 5,186 OTUs of microprokaryotes were obtained by high-throughput sequencing in this study,including 1,995,525 reads and5,044 OTUs of bacteria,3,823 reads and 142 OTUs of archaea.Bacteria were important contributors to both the biomass and diversity of the microprokaryotic community,while archaea had less influences on the microprokaryotes.There were 82 species,408 genus,64 classes in 38 phyla of bacteria detected in this study,and only1 species,6 genus,7 classes in 7 phyla of archaea were detected.Proteobacteria dominated in both DNA reads and OTU richness of microprokaryotes,in which γ-proteobacteria was the first dominant class,followed by α-proteobacteria.In addition,most OTUs identified to the species level were psychrophile or psychrotolerant species.The sums of abundant and rare OTUs of microprokaryotes were 123 OTUs and 3,563 OTUs respectively.Bacteria dominated in both abundant OTUs and rare OTUs,while archaea mainly contributed to the diversity of rare OTUs.In molecular ecological network of microprokaryotes,the proportion of positive correlations was88.19%,which suggested the cooperative or symbiotic relationships between species.Furthermore,as the central nodes of the network,δ-proteobacteria,ε-proteobacteria,Nitrospinia,Nitrospira,Rhodothermia,Polyangia,Thermoanaerobia and Ignavibacteria played important roles in microprokaryotes in the surface sediments from the Western Arctic Ocean.(3)TOC ranged from 0.13% to 1.98% in the surface sediments of the Western Arctic Ocean,with higher levels in B09 station of the Bering Sea shelf and R11 station of the Chukchi Sea slope.BSi ranged between 1.07% and 12.87%,which were higher in stations B08 and B08＿1 of the transition zone between the Bering Sea basin and the Bering Sea shelf.TN was in the range of 0.04%-0.24%,with high levels in B10 station of Bering Sea shelf and C21 station in Chukchi Sea continental slope.TP ranged between 0.02% and 0.13%,which was high in R03 station of the northern Bering Strait.Based on the molar ratios of TOC/TN,TOC in the surface sediments of the Western Arctic Ocean was mainly originated from marine sources.The molar ratios of BSi/TOC were in the range of 0.71 and 9.38,with an average of 4.38,which indicated the importance of silicate pump in the output and burial of organic carbon.(4)Positive correlations between biogenic elements indicated the similar sources of biogenic elements in the surface sediments from the Western Arctic Ocean.TOC,BSi,TN,and TP showed significantly positive correlations with eukaryotic algae,especially diatoms,which suggested diatoms were important sources of these biogenic elements.TN and TP were important factors affecting relative abundance of microprokaryotes,and BSi,TN,TP influenced diversity of bacteria and archaea.RDA analysis showed that TN,TP,BSi and BSi/TOC affected the distribution of the Mediophyceae,the first abundant class in microeukaryotes,suggesting mediophytes were important contributors to TN,TP and silicate pump in the surface sediments of the Western Arctic Ocean.In addition,TN and TP affected the distribution of γ-proteobacteria and α-proteobacteria,suggesting that nutrients were important factors affecting bacterial abundance.While BSi and BSi/TOC influenced the distribution of the archaea,methanogens and thermophiles,which indicated the potential relationships between some groups of archaea and siliceous pump.