Effects Of Sulfur Biogeochemical Cycle On Bioavailability Of Heavy Metals And Microbe Community Structure

The oxidation and reduction of heavy metals in soil involves both chemical and microbial process. Microbial oxidation and reduction of S, the necessary nutriment and considered as the minimum risk acidification, may influence changes in Cu and Zn solubility, toxicity and bioavailability, either through direct oxidation of metal sulfides or indirectly by the release of metal complexing agents into the soil solution. Knowledge of how heavy elements affected by sulfides and element sulfur, is an important factor in understanding their biogeochemical cycling in soil and high efficient combined bioremediation technology for soil metal pollution. In the present study, a combination of laboratory incubation experiment, glasshouse experiments, microbiology and molecular biology techniques (PCR-DGGE) was conducted under controlled environment conditions to compare the efficiency of heavy metals solubility, analyze the microbial community structures and investigate the potential to increase metal uptake by E.splendens under treatment of different types of sulfide and element sulfur. The major results obtained are as follows:SOB was isolated from sewage sludge. It was showed that SOB has significantly tolerance and absorbability of heavy metals in soil. At a SOB concentration of 14.4mg/kg, the highest absorbability efficiency of Cu and Zn was reached (2.8 mg/kg, 1.4mg/kg). SOB had the best heavy metal absorbability as pH value as 5.0.Elemental sulphur has potential to solubilize soil metals. Sulfur treatment decreased soil solution pH from 8.0 on day 1 to 4.5 on day 65. As compared to control, addition of 200 mgS·kg^-1 soil resulted in a continuous increase in concentration of NH₄NO₃-extracted Cu, Zn, as 5.1, 9.4 higher than control on day 65. The combination of sulfur and SOB increased the reaction speed. The total soluble metals/total soil metals ratio decreased in the order of Zn>Cu, which can be explained by higher sensitivity of Zn solubility to soil pH. Na₂S₂O₃ treatment increased soil solution pHand the bioavailability of Cu, the concentration of NtLjNOa-extracted Cu increased 20 times higher than that of control on day 65.On the aspect of microbiology, denaturing gradient gel electrophoresis (DGGE) of specifically amplified 16S rDNA gene fragments had been used to evaluate microbial community changes in soils added by different sulfides during the experiment. PCR-DGGE analysis showed distinct diversity of microbial community structures of different soils treated by sulfides and element sulfur. Shannon diversity index analysis and two standard methods dimensioning techniques (PCA) were used to analysis the DGGE result. It was showed that Shannon diversity index analysis of soil microorganism were lower than that of the control (3.32). Among the treatments, soils treated by element sulfur had the lowest Shannon diversity index (2.17) compared to treatments of Na2S2O3, Na2SO3 and the control. PCA analyses the data directly by a binary band-matching table. The two principal components (PC) explained a low of the total variation (PC 1 = 34.225%;PC 2 = 28.401%). The PCA could separate the different groups completely, most of the soil samples of one sulfides treatment were localised together in the same area."Plant-chemical additive-microbe" combined structure was successfully set up. E.splendens, sulfur and SOB was combined together, consequently remarkably improved the phytoextract capability of plant. The Cu accumulation in the plant was found to be higher than that of Zn, showing that phytoextraction efficiency of Cu by E.splendens was 2-5 higher than control.