Effects Of Phosphate On Microbial Iron Reduction In Different Paddy Soil

Phosphorus transformation and fate in paddy soil has been of great concern in the soilchemistry. At present, most research has focused on the environmental impact associated withsoil phosphorus transformation, and exploring the relationship between phosphorus and soilcritical biochemical processes is relatively less. The effectiveness of soil phosphorus isheavily influenced by transformation of iron form to a great extent, so research on ironreduction in paddy soil regulates transformation of soil phosphorus and understanding therelationship between iron reduction and transformation of soil phosphorus has the vitalsignificance..In this experiment, we chose paddy soil from Yongji, Hanzhong, Jiangxi.Afteradding different concentrations of phosphate, different concentrations of phosphate andferrihydrite, ferrihydrite, we used slurry anaerobic culture as testing method. Through thestudy of their impact on available phosphorus concentration,water-soluble phosphorus andiron reduction process, we draw the following conclusions:(1). Adding ferrihydrite can promote the accumulation of Fe(II) concentrations.Maximum accumulation of Fe(II)(a) was6.3645mg/g in Fe treatment of Yongji paddy soiland higher than the control (CK) significantly. But adding ferrihydrite iron reduction processhad a lag phenomenon in the early stage of incubation. The reason may be that sulfate adsorptsurface of ferrihydrite, thereby preventing the iron reducers contact with ferrihydrite. Inaddition,sulphates may also act as the electron acceptor competition role. With the progress ofreaction, ferrihydrite can still be reduced in the soil.For the effective phosphorus and watersoluble phosphorus, Adding ferrihydrite has a fixed role on the soil phosphorus. Availablephosphorus and water soluble in Yongji paddy soil phosphorus overall trends significantlylower than CK. Late in the culture, Compared with CK, Available phosphorus concentrationreduced12.62μg/g soil and water-soluble phosphorus reduced0.1418mg/kg in Yongji paddy.(2).Adding potassium dihydrogen phosphate inhibited iron reduction process, Comparedwith CK, Fe (II) concentration and showed a downward trend overall in Hanzhong, Yongji paddy soil. Late in the culture, Fe(II) concentrations reduced0.23mg/g and0.02mg/grespectively in Hanzhong and Yongji paddy soil. For the available phosphorus and watersoluble phosphorus, adding potassium dihydrogen phosphate promoted the increase ofeffective phosphorus and water soluble phosphorus concentration; adding ammoniumdihydrogen phosphate promoted promoted the increase of effective phosphorus and slightlyinhibited iron reduction process.Different concentrations of ammonium dihydrogenphosphate was no significant difference on the influence of concentration of Fe(II).Presumably due to N of the ammonium dihydrogen phosphat to provide a sufficientamount of N source for iron reducer, enhancing iron reduction process weaken the inhibitionof ammonium dihydrogen phosphat on the iron reduction process.(3). Adding potassium dihydrogen phosphate and iron oxide inhibited phosphorus releaseand reduced initial concentration of Fe (II). However, with prolonged incubation time, theferrihydrite can be still can reduced in soils. As for available phosphorus and water solublephosphorus, compared to adding potassium dihydrogen phosphate treatment, addingpotassium dihydrogen phosphate inhibited the increase of effective phosphorus and watersoluble phosphorus concentration.the effective phosphorus and water soluble phosphorusoverall trended significantly lower in Hanzhong, Yongji paddy soil and early in the culturedecline was obvious; adding ammonium dihydrogen phosphate and iron oxide promotedavailable phosphorus fixed, inhibited iron reduction process and the high concentration ofammonium dihydrogen phosphate significantly inhibited iron reduction. From Fe (II)maximum cumulative(a) can be seen, compared with Fe treatment,adding ferrihydrite andhigh concentration of ammonium dihydrogen phosphate（Fe+300μg/g P，Fe+400μg/g P） reduced2.8%,3.5%, and the difference was significant. While adding ferrihydrite and lowconcentration of ammonium dihydrogen phosphate（Fe+50μg/g P，Fe+100μg/g P，Fe+200μg/g P）increased1.8%,0.66%,0.07%.As for available phosphorus, compared with ammoniumdihydrogen phosphate treatment, adding ammonium dihydrogen phosphate and iron oxide hada fixed role on available phosphorus and available phosphorus concentration had a overalldownward trend. And phosphorus concentration downward trend is obvious at the first fewdays.With the reaction continuing,this decline gradually weakened.(4).Adding phosphate and ferrihydrite in acidic paddy soil from Yichun, availablephosphorus and Fe(II) concentration had similar trend. In the control group (CK,100μg/g P,300μg/g P), Compared with CK，in the early stage of incubation adding phosphate reducedconcentrations of Fe(II) as phosphate concentration increased and after20days there was nosignificant difference. While available phosphorus concentration was always higher thanCK;Fe group(Fe,Fe+100μg/g P,Fe+300μg/gP)had remarkable influence on iron reduction.Firstly, Fe treatment reduced the iron reduction rate and improved phosphateavailability significantly. Compared with CK, Fe(II) concentration increased3.11μg/g andphosphate availability reduced12.62μg/g on the40th day;Secondly, adding ferrihydrite anddifferent concentrations of phosphate (Fe+100μg/g P,Fe+300μg/g P),iron reduction lagedbehind CK in the early stage of incubation. Then it raised remarkably and high phosphorusconcentration in particular. On the whole, phosphorus availability were lower than onlyadding different concentrations of phosphate treament.