Characteristics Of Phosphorus Forms And Microbial Community Structures In The River Sediments

GradeⅣ,GradeⅤ,and inferior Grade V water accounts for a higher proportion,and fresh water eutrophicates seriously in China.The excessive phosphorus is one of the important factors casuing eutrophication.Sediments are important storages of phosphorus in rvier ecosystems.Phosphorus release from sediments to the overlying water,which is an important factor leading to water eutrophication.Microorganisms play an important role in the biogeochemical cycling of phosphorus by ways of the dissolution of inorganic phosphorus,mineralization of organophosphorus and biological fixation of phosphorus.Therefore,the studies on various forms of phosphorus,characteristics of microbial community structures,and the connection between them were conducted in the sediments along the Shiwuli River.The results showed as follows:（1）The contents of TP,IP and OP were higher in the sediments near the river entrance to the lake and midstream（sampling point 7）,and lowest at the upstream.TP mainly existed in the form of IP in the sediments along the Shiwuli River.The organophosphorus contents with different activities showed:Moderately labile OP>Nonlabile OP>Labile OP.On the whole,the contents of labile OP and nonlabile OP were relatively higher in the sediments at the downstream,and Moderately labile OP were relatively higher in the sediments at the midstream.The contents of available phosphorus were much higher than46 mg·kg^-1,indicating that the phosphorus contents have been overloaded in the sediments.Comparing other reaches of river,the contents of Olsen-P,RDP and WSP were relatively higher in the sediments at the midstream,however the contents of AAP were relatively higher near the river entrance to the lake.（2）MBP,MBC and MBC/MBP value showed higher value in the sediments at the downstream except near the entrance to the lake.And the MBC/MBP value was significantly higher at the downstream than the C/P value at other reaches of river,indicating that the microorganisms have a high ability to assimilate phosphorus in the sediments.The contents of total sediment microorganism PLFAs and different group microbial PLFAs contents were higher in the sediments at the downstream than these at other river reaches far away from the lake entrance,moreover,bacteria were the largest proportion of the microbial communities,followed by fungi and actinomycetes.（3）High throughput sequencing studies showed that,the OTU number,Chao1,ACE,Simpson index and Shannon index was higher in the downstream near the entrance to the lake.The dominant bacteria at the phylum level included:Proteobacteria,Bacteroidetes,Acidobacteria,Euryarchaeota,Actinobacteria,Chloroflexi,and Firmicutes.The dominant bacteria at the class level included:Betaproteobacteria,Gammaproteobacteria,Anaerolineae,Deltaproteobacteria,Clostridia,and Alphaproteobacteria.The dominant bacteria at the genus level mainly included:Dechloromonas,Leptolinea,Smithella,Christensenellaceae＿R-7＿group,and Flavobacterium.Dominant phosphate solubilizing bacteria included:Thiobacillus,Flavobacterium,Acinetobacter.（4）The correlation analysis results showed that total PLFAs,PLFAs content of fungi,bacteria and anaerobion and G+/G–value,fungal/bacterial value showed signicant correlation with various phosphorus fractions.In the bacterial community,Proteobacteria,Firmicutes,and Actinobacteria,Acidobacteria owned signicant correlation with various phosphorus fractions.Flavobacterium and Thiobacillus significantly correlated with various phosphorus fractions.Redundancy analysis indicated that labile OP,AAP,IP and TP was significantly related to sediments microbial community structure and bacterial community structure at the downstream near the entrance to the lake（sample point 1,sample point 2）;fulvic acid-OP,RDP,nonlabile OP showed signicant correlation with sediments microbial community structure and bacterial community structure at the downstream reach far away from the lake entrance（sample point 3,sample point 4,sample point 5）;IP and TP was significantly related to sediments microbial community structure and bacterial community structure at the upstream（sample point 8）.