| Microbial Fe(III) reduction in paddy soil is an important anaerobic biochemical process,which has a significant influence on the chemical behavior of paddy soil. Biochar has a high porosity, large specific surface area and other properties, therefore there are more research for global warming and increased carbon sequestration. Both biochar and microbial Fe(III) reduction has certain inhibitory effect on greenhouse gases, but there is still little research on the relationship between the two. The experiment is divided into the following four parts: add different amounts of biochar and biochar in different particle sizes to different kinds of paddy soil;in the presence of biochar add additional electron acceptor and donor to the system to discuss changes of Fe(II) concentration and pH values with different biochar and organic carbon(glucose, acetate, pyruvate and lactate) in soil mud, characterized by Logistic model for reducing Fe(III) fitted analysis; In order to study biochar in different particle sizes and different adsorption time on the adsorption of different carbon sources, as well as its effects on iron reduction in paddy soil effects, and the effect of different carbon sources on iron reducing characteristics of soil in addition of treated biochar, collect Jilin(JL) and Guizhou(GZ) paddy soil as test soil, using thermostatic mud anaerobic test mode and mixed culture of soil microbial community. And the varying concentrations of Fe(â…¡) and pH values were measured. The experiment get the following conclusions:(1)Adding biochar in different paddy soils can increase the initial pH value of the system. With the anaerobic process, its impact on the pH value gradually weakened, in the latter part of the culture pH and control keep consistent. It shows the effect of biochar on paddy soil pH value is transient, not lasting changes in soil pH. Make it clear about the understanding of "biochar might have an increased risk of soil pH value".(2) In different types of paddy soil(acidic, neutral and alkaline paddy soil), with the addition of biochar, the amount of system Fe(II) cumulative concentration showed significant increasing trend, iron reduction eigenvalues(iron reduction potential, the maximum reduction rate of iron and iron reduction rate corresponding to the maximum time) had significant differences. It showed that adding biochar has the ability to control iron reduction in paddy soils, suggesting the addition of biochar can regulate the main paddy soil biochemical processes, showing the potential environmental significance.(3) The particle size of the added biochar has a significant impact on paddy soil microbial iron reduction. The Fe(II) concentration and accumulation of biochar negative correlation between particle size, the smaller the particle size the greater the system Fe(II) concentrations. It shows that the ability of biochar to control the iron reduction process has significant correlation with the size of the surface area of biochar, and partly reveals the internal mechanism of biochar to regulate iron reduction in paddy soils, namely by changing the surface adsorption process may significantly promote microbial iron reduction.(4) The results showed that iron reduction was different according to the types of paddy soils and carbon source when adding biochar. The addition of biochar in two paddy soils(YJ and NC) can promote Fe(III) reduction process. The effects of carbon source on Fe(III) reduction in YJ paddy soil were more significant than those in NC paddy soil with biochar. Lactate, pyruvate and glucose can be well utilized by iron reducing microorganism in both paddy soils, while acetate lagged the reduction of Fe(III),especially in YJ paddy soil. Under the overall comparison, the treatment with lactate had the maximum Fe(III) reduction rate and took the shortest time, illustating that lactate was the dominative carbon source for Fe(III) reduction in both paddy soils. The changes of soil pH caused by fermentative carbon source addition in NC paddy soil during anaerobic incubation was more obvious than that in YJ paddy soil, speculating that microorganisms in YJ paddy soil had a better utilization of H2 produced by carbon source fermentation than that in NC paddy soil.(5) In the slurry culture experiments, all of the three particle sizes absorbed with glucose and pyruvate biochar will cause the Fe(II) accumulation increase, the Fe(III) reduction rate increase, and the time to reach equilibrium shorten; the biochar adsorbed with fermenting organic carbon can cause the pH of the reaction system dramatically decrease.(6) In the microbial community culture experiments, in the same particle size, the longer the adsorption time, the more the cumulative amount of Fe(II); at the same adsorption time, the larger the particle size of biochar, the lower the cumulative volume Fe(II); adding adsorbed biochar will reduce the pH of the system. |
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