Microbial Communities Evolution And Its Influence On Soil Forming Process Of Bauxite Residue

Bauxite residue is the solid waste with the largest emissions from the non-ferrous metal industry.It is characterized by high alkalinity and salinity,which can hardly be utilized and mainly stored on land,called bauxite residue disposal areas(BRDA).The storage of such large volumes of bauxite residue not only occupied land resources but also seriously threatened the surrounding ecological security.Thus,the large-scale disposal of bauxite residue is of great importance to the sustainable development of the alumina industry.Transforming the bauxite residue to a soil-like material is the most promising way to achieve large-scale disposal of bauxite residue.Microorganisms play important roles in the soil formation process,including organic matter degradation,nutrient cycling,and soil structure formation and stabilization.However,there are few reports focused on the changes in composition and function of microbial community during the soil-forming process of bauxite residue,which limited our comprehensive understanding of the soil-forming process in bauxite residue.Based on the natural pedogenesis on bauxite residue deposit areas,the succession of microbial communities under natural weathering processes was investigated by using a high-throughput sequencing technique and fluorescence quantitative PCR.According to the driving factors to the succession of microbial communities,we investigated the effects of phosphogypsum and straw or their combination on the physicochemical properties and its influence on microbial communities in bauxite residue.Eventually,the effects of phosphogypsum and straw on microbial carbon metabolism and its potential function mechanism on the soil-forming processes under natural conditions in bauxite residue were discussed.In this study,the succession of microbial communities and their driving factors under natural conditions in bauxite residue were studied by the combination of field investigation and indoor simulation.(1)Long-term natural weathering process significantly increased the microbial biomass carbon and nitrogen,as well as the enzyme activities in bauxite residue disposal areas(BRDAs).The predominant bacterial groups in fresh bauxite residue are Firmicutes,Actinobacteria,Proteobacteria,and Chloroflexi which are resistant to high salinity and alkalinity.In the vegetation area,the predominant bacterial group shifted to those dominated by Firmicutes,Actinobacteria,Proteobacteria,Chloroflexi,Planctomycetes,and Acidobacteria,which is similar to that in soil.The diversity and composition of the bacterial community were mainly influenced by the physicochemical properties in bauxite residue,in which total nitrogen,organic carbon,and p H are the majority driving factors to its succession.(2)Application of phosphogypsum and straw significantly can improve the physiochemical properties of bauxite residue.Under the combination of phosphogypsum and straw,the p H value in bauxite residue decreased to 8.0,and the contents of organic matter(TOC),total nitrogen(TN,and available phosphorus(AP)significantly increased.Moreover,the combination of phosphogypsum and straw significantly increased the microbial biomass and enzyme activities in bauxite residue.Phosphogypsum reduces the alkalinity in bauxite residue,while straw supplies nutrients.They can jointly promote the development of microorganisms,which helps to promote the nutrient balance and enzyme activity in the soil-forming process of bauxite residue.(3)The combined addition of phosphogypsum and straw significantly increased the relative abundance of Devosiaceae,Caulobacteraceae,Sphingobacteriaceae,Xanthomonadaceae,and Rhizobiaceae,which are important in degrading organic matter,fixing carbon,and fixing nitrogen.The changes in bacterial diversity and composition were mainly affected by the physicochemical properties in bauxite residue,in which organic carbon(TOC)and exchangeable sodium(Na~+)were the main factors.(4)During the soil-forming process of bauxite residue,the addition of straw significantly promotes the activity of carbon metabolism.The combination of phosphogypsum and straw significantly increased the utilization of amino acids and sugars,whereas decreased the utilization of ester,amine,and carboxylic acid.The increased organic carbon and decreased p H influence the utilization of different carbon sources by changing the microbial community structure,and then changing the carbon source metabolism of microorganisms in bauxite residue.(5)The application of phosphogypsum and organic matter significantly increased the abundance of nif H gene and diversity of nitrogen-fixing bacteria communities.Bacillaceae,Phyllobacteriaceae,and Methylococcaceae were the dominant population of the nitrogen-fixing bacterial communities in fresh bauxite residue.Under the stimulation of straw and phosphogypsum,the relative abundance of Rhodospirillaceae and Rhizobiaceae increased significantly,and that of Bacillus and Phyllobacteriaceae decreased significantly.According to the correlation analysis,the abundance and diversity of nitrogen-fixing bacteria were negatively correlated with p H,electrical conductivity(EC),exchangeable sodium(Na~+),and the ratio of exchangeable sodium(ESP),but positively correlated with organic carbon(TOC),total nitrogen(TN),available phosphorus(AP)and available potassium(AK)contents.Compared to the long-term natural weathering process,human intervention can drive the succession of the microbial community in a short time scale,thus accelerating the soil-forming process of bauxite residue.Human intervention further reduced the alkalinity and salinity in bauxite residue,improved the physical structure of bauxite residue,and increased the richness and diversity of the bacterial community,accelerating the soil formation in bauxite residue.Figures 66,Tables 35,References 277...