The Relationship Between Microbial Fe(Ⅲ) Reduction Progress And Phosphate Concentration

Microbial Fe(III) reduction progress happened in flooded paddy soil is not only theimportant link of iron geobiochemical circulation, but also involved in the geochemicalcirculation of phosphorus. The slurry and bacterial suspension from six kinds of paddy soilwere added different concentrations of phosphate, and then incubated under anaerobicconditions. The concentrations of Fe(II), available phosphorus and Ph value were measuredat certain times during the incubation. This research studied the relationship betweenmicrobial Fe(III) reduction progress and phosphate concentration. Adsorption of phosphate byFe (OH)3suspention experiment was designed to validate mechanism. Based on findingsof this study the following conclusions have been drawn:(1) In slurry anaerobic incubation experiments, the final Fe(II) accumulation amountwas different, for the amount of Fe(III) could be reduced by microorganisms was different.The sodium dihydrogen phosphate had little effect on Fe(III) reduction because it wasimmobilized by solid matter in soil when it was added. It could be found that the maximumFe(II) accumulation, the maximum rate of Fe(III) reduction and the corresponding times weresignificantly different between different treatments of some soils.(2) Available phosphorus in soils of different pH values presented various change trendsin slurry anaerobic incubation. The concentration of available phosphorus was increasing asphosphate was released by soil organic matter decomposition in acid paddy soil. It was alsorelated with microbial Fe(III) reduction. The more the maximum Fe(II) accumulation, themore the increasement of available phosphorus. Phosphate added in alkaline paddy soil wasimmobilized during the earlier stage of incubation, because organic acid increased free ioniccalcium which increased the absorption capacity of phosphate by iron.(3) CCA analysis could represent the relevant relationships between microbial Fe(III)reduction, variation of available phosphorus and environmental factors. The results of CCAanalysis further confirmed that Fe(II) accumulation was mainly from amorphous iron oxide.The availability of phosphorus was improved when phosphate was released by microbialFe(III) reduction. The decomposition of organic carbon provided carbon source and electrondonor for microorganisms. (4) There were great difference of microbial Fe(III) reduction between differentbacterial suspension incubation systems, for species and quality of microorganisms were quitedifferent. Adding31-124mg/L phosphorus could meet the physiological needs ofmicroorganism in bacterial suspension incubation, and high concentrations of phosphate hadan inhibitory effect on Fe(III) reduction.(5) The concentration of available phosphorus decreased a little during bacterialsuspension incubation. Phosphate was absorbed by amorphous iron oxide and some portion ofphosphate was translated into microbial biomass phosphorus. Adsorption experimentconfirmed that phosphate could be absorbed by amorphous iron oxide, and adsorptioncapacity increased as the concentration of phosphate increased.