Responses Mechanism Of Endogenous Phosphorus Release From Sediments To Phosphate Solubilizing Bacteria In Overwinter Period And The Effect Of Cyanobacteria Recruitment

The release of endogenous phosphorus from lacustrine sediment is a key element of freshwater eutrophication.The phosphate-solubilizing bacteria（PSB）in sediments may affect phosphorus migration and transformation during the growth of cyanobacteria,which may lead to the release of phosphorus from sediments and contribute to water eutrophication.To study responses mechanism of endogenous phosphorus release from sediments to PSB in overwinter period and the effect of cyanobacteria recruitment,samples in Meiliang Bay were collected during the dormancy and resuscitation phases of cyanobacteria.The physicochemical properties of the overlying water and sediment in Meiliang Bay were investigated,and the influence of microorganisms on the release of endogenous phosphorus was analyzed to determine the risk of release of sediment as a"source"of phosphorus.Next,bacteria with phosphate solubilization function were screened,and the bacteria-algae experimental simulation system was constructed to reveal the effect of cyanobacterial resuscitation due to the induction of endogenous phosphorus release by PSB.The main research results are as follows:（1）Moderate eutrophication of water in Meliang Bay during the dormancy period and resuscitation period of cyanobacteria.Concentration of total phosphorus（TP）during resuscitation period of cyanobacteria（0.11-0.24 mg/L）>dormancy period of cyanobacteria（0.09-0.23 mg/L）in overlying water,The opposite trend in sediment during overwinter period of cyanobacteria（722.3-1059 mg/kg）>recruitment period of cyanobacteria（621.6-895.8 mg/kg）.Most of the phosphorus in the sediment was inorganic phosphorus（IP）,consisting mainly of iron/aluminum-bound phosphate（Na OH-P）,and they were relatively easier to migrate out of sediment to the overlying water.During the cyanobacterial recruitment period,the mid-surface sediments contained more bioavailable phosphorus（Na OH-P）.The proliferation of PSB（Proteobacteria,Bacteroidota,Firmicutes）drove sediment phosphorus release.The largest relative abundance of PSB（Proteobacteria）showed a significant positive correlation with organic phosphorus（OP）concentration（P<0.01）during recruitment period of cyanobacteria,and PSB（Proteobacteria,Actinobacteriota,the Proteobacteria phylum Gammaproteobacteria,and the Proteobacteria phylum Alphaproteobacteria）were positively correlated with equilibrium phosphorus concentration（EPC₀）（P<0.05）.The sediment as phosphorus sources had high relative abundance of PSB in the cyanobacterial resuscitation stage,and the risk of endogenous phosphorus release was significantly higher than during the dormant overwintering phase of cyanobacteria.（2）Fourteen strains of PSB,including six inorganic phosphate-solubilizing bacteria（IPB）and eight organic phosphate-solubilizing bacteria（OPB）,were identified as belonging to the genus Paraburkholderia fungorum from the sediment with phosphorus"source"properties during the cyanobacterial recruitment period,but the differences between the strains were obvious.The phosphate solubilization capacity of IPB was greater than that of OPB,and the highest soluble reactive phosphorus（SRP）concentration was up to 292.45 mg/L.The SRP concentration showed a significant negative correlation with p H（P<0.01）.Gluconic acid was the main mechanism of phospholysis by IPB,while the mechanism of phospholysis by OPB was presumed to be the combined action of organic acids and phosphatases.The release fluxes of TP,total nitrogen（TN）and total iron（Fe）at the sediment-water interface were positive,with maximum values of 0.64,15.0 and 5.02 mg/（m² d）,respectively.The risk of endogenous phosphorus release from sediments was high under the appropriate number of PSB.（3）The abundance of the dominant PSB Paraburkholderia fungorum（Burkholderia-Caballeronia-Paraburkholderia）was correlated with chlorophyll a（Chl a）and Fe in overlying water,phosphorus（P）and Fe（II）in pore water,and DGT-P,DGT-Fe,IP,OP,Na OH-P,and algal effective state phosphorus（AAP）concentrations in sediment were positively correlated,especially with Chl a and AAP concentrations（P<0.05）.The Chl a concentrations reached peaks of 344.8 ug/L and297.1 ug/L successively in OPB5(OD₆₀₀=0.8)and IPB3(OD₆₀₀=0.8)groups.SRP and Fe（II）concentrations could reach 0.51 mg/L and 33.56 mg/L in pore water,respectively.And the sediment DGT-P and DGT-Fe concentrations were relatively reduced in the experimental group with OPB5 inserted under the sediment-water interface.PSB mainly regulates AAP,inducing endogenous phosphorus leaching to pore water and then diffusing across the sediment-water interface to the overlying water,producing the effect of cyanobacteria recruitment.The results provide a valuable reference for possible ecological inducers of cyanobacterial recruitment in spring,which we hope can be provided theoretical support for the early governance of cyanobacterial blooms.