Distribution Characteristics Of Phosphorus In The Sediments Of Lake Taihu And The Influence Mechanism Of Phosphate Solubilizing Bacteria

Lake eutrophication seriously is harmful for the aquatic ecosystems and drinking water safety.The eutrophication of lakes and cyanobacteria blooms were mainly caused by the release of phosphorus(P)from the sediments in shallow lakes.Therefore,this paper takes Taihu Lake,China's third largest freshwater lake,as the research object.We systematically investigates the physical and chemical properties of overlying water,and the compositions of forms of P fractions in the sediments of North Taihu Lake and Changxing by the Standards Measurements and Testing Program(SMT protocol).Then we analyze the influence of microorganisms on the release of phosphorus,and finally isolate and identify several strains of bacteria with strong ability to dissolve phosphorus,and preliminarily explore the mechanism of phosphorus dissolution.For the sediments of North Taihu Lake and Changxing,the results of SMT method for the separation and extraction of different forms of phosphorus showed that the average value of TP content in the sediments was about 0.44 mg/g.The variation ranges of TP were 0.30-0.46 mg/g,0.40-0.62 mg/g,respectively,which level is in the middle and lower reaches compared with other lakes of the same type.Calcium bound phosphorus(HCl-P)is the main component of Total phosphorus(TP)in the deposition,with an average ratio of 41.0% and 59.1%,followed by Iron-aluminum bound phosphorus(Na OH-P)and the lowest Organophosphorus(OP).Among them,the proportions of OP and Na OH-P content in TP are similar;HCl-P is the main form of IP,which has a significant positive correlation with TP content and a significant negative correlation with OP content.The 16 S rDNA technique was used to analyze the distribution of microbial abundance in sediments,and it was found that Proteobacteria,Chloroflexi and Nitrospirae had great abundance at various depths.From the correlation between the microbial community in different depths of sediment and the content of different forms of phosphorus,it is mainly positively correlated with OP content(p <0.01),and significantly negatively correlated with Na OH-P(p <0.01).The spatial distribution of phosphate-decomposing bacteria(PSB)in the sediments of North Taihu Lake was further analyzed by plate culture method.The results showed that the abundance of PSB in the sediment was high,and the number of inorganic phosphate-depleting bacteria(IPB)was higher than that of organic phosphate-depleting bacteria(OPB).The trend is decreasing from the surface layer to the bottom layer,and the number of PSB in the surface layer and the middle layer is similar.Four strains of IPB were isolated and selected,including Acinetobacter sp.and Pseudomonas sp..The results of the determination of phosphate-dissolving ability show that the most efficient phosphate-dissolving bacteria can transform and increase 243.88 mg/L orthophosphate.Its mechanism is to secrete small molecule organic acids(mainly gluconic acid,propionic acid and succinic acid)to dissolve insoluble phosphoric acid salt.