Study On The Mechanism Of Sulfur Metabolism Of Microorganisms And Its Influencing Factors In Coastal Saline-alkali Soil

The physical and chemical factors such as salinity and pH of coastal saline-alkalisoil change significantly under long-term seawater erosion.Many studies have proved that salinity is the main factor leading to the change of soil microbial community,but there are few studies on salinity affecting sulfur metabolizing related microbial community.At the same time,salt ions increased with water evaporation,which caused significant differences in the properties of coastal saline soil with its depth.Many studies only focus on the change of soil surface microbial community,while the influence of soil depth change on microbial community including sulfur metabolizing microbial community remains unclear.In this study,several samples of coastal salinized soil and inland non-salinized soil were collected,the effects of changes in physical and chemical factors such as electrical conductivity（an indicator reflecting soil salinity）,pH and soil depth on soil sulfur metabolizing microbial community were studied by metgenomics or 16S r RNA gene sequencing.The main contents and results of the study are as follows.（1）To study the impact of soil salinity on microbial sulfur metabolism in coastal saline-alkaline soil,we selected 44 soil samples from Dongying（coastal saline-alkali soil）and Qufu（inland soil）city of China.We detected the physical and chemical factors of soil samples,isolated and cultivated the sulfur related microorganisms,and performed the 16S r RNA gene sequencing for these soil samples.We have isolated2680 bacterial strains from soils with different salinity.Those bacteria were classified into two groups,H₂S-releasing bacteria（HSRB）and H₂S-non-releasing bacteria（HSn RB）according to whether H₂S volatilized or not.Linear regression analysis showed that H₂S production in soil was positively correlated with soil salinity（electrical conductivity）and the proportion of HSRB.According to the 16S r RNA gene sequencing results of the two soils,it was found that the richness and diversity of microbial communities in saline-alkaline soil and non-saline-alkaline soil were significantly different,and the increase of electrical conductivity significantly reduced the diversity of microbial communities.In salinized soil,the abundance of Proteobacteria and Bacteroidetes increased significantly.Prediction analysis by PICRUSTs showed that the abundance of genes related to sulfur metabolism in salinized soil was significantly changed,and the abundance of two key H₂S oxidation genes（sqr and sox B）was significantly decreased,which was consistent with the results of HSRB proportion.In conclusion,high salinity significantly affects the microbial community structure in coastal saline-alkaline soil.The increase of salinity leads to the decrease of sulfur-oxidizing bacteria content and the increase of sulfur-reducing bacteria content.The change of sulfur-metabolizing bacteria community further affects the microbial sulfur metabolic cycle,leading to the increase of H₂S production in soil.（2）To study the influence of soil depth on sulfur-metabolizing communities in coastal salinized soil,we selected 12 soil samples with different degrees of salinization and different depths from Dongying city,analyzed the concentrations of important sulfur compounds and chemical factors,and conducted the metagenomics sequencing of soil samples.The concentrations of sulfur compounds in soil were significantly correlated with soil depth,and soil depth influenced the sulfur compounds more strongly than soil salinity.Both soil depth and salinity affect the abundance of bacteria and archaea.The surface soil harbored abundant archaea,while the deep soil harbored more bacteria.The main microorganisms were Proteobacteria,Euryarchaeota,Bacteroidetes,Balneolaeota phyla in the surface soil and Proteobacteria,Acidobacteria and Chloroflexi phyla in the deep soil,respectively.The alpha diversity and NMDS analysis showed that the microbial communities were significantly different with the soil depth and salinity.In addition,we classify the genes associated with the sulfur cycle into sulfur oxidation,sulfur reduction,sulfate assimilation,organic sulfur metabolism and sulfur transformation groups.Gene abundance analysis showed that soil sulfur metabolism gene abundance was significantly different with soil depths,sulfur oxidation gene abundance in deep soils is lower than surface soil.Others such as sulfur reduction/sulfur assimilation/organic sulfur metabolism and sulfur transformation had the opposite gene tendency.The results of RDA analysis showed that the environmental conditions had a significant effect on sulfur metabolism genes,and the concentration of sulfide significantly affected the surface and sub-surface of low salinity soil.Correlation analysis of microbial communities and sulfur gene abundance further showed that Bacteroidetes and Balneolaeota cluster together,Proteobacteria clustered together with Acidobacteria,which was consistent with the results of microbial communities in soil.All kinds of sulfur metabolizing genes were distributed in the two clusters mentioned above.Our results proved that microbial sulfur metabolism actively participates in sulfur biological cycles of salinized soil,and that soil depth,rather than salinity,has more influence on these processes and the microbial community.Together,our results provide an important scientific basis for fully understanding the sulfur metabolic cycle and its influencing factors in salinized soil,provide a theoretical basis for the utilization of soil sulfur,and provide a new sight for the regulation of this special terrestrial sulfur cycle.