| The migration and transformation of sulfur is closely related to carbon sources.However,knowledge on the co-occurrence patterns of sulfur-metabolizing bacteria and other carbon-consuming microorganisms in constructed wetlands（CWs）is limited.This experiment first investigated the microbial communities in the Intertidal Wetland Sediment（IWS）of the Yellow River Delta at four depths（0-5 cm,5-10 cm,10-15 cm,and 15-20 cm）and in four seasons（spring,summer,autumn,and winter）.To clarify the diversity and distribution characteristics of microbial communities under the influence of different environmental factors,and to select IWS rich in sulfur-metabolizing and carbon-consuming functional bacteria as microbial inoculants.Secondly,IWS were inoculated into constructed wetland as microbial inoculants to construct microbial.IWS-enhanced CWs（IWS-CWs）planted with Phragmites australis（PA+）and unplanted ones（CT+）were set up as experimental groups,and traditional constructed wetlands（PA,CT）were set up as control groups.The influent was simulated domestic sewage（sulfate concentration:120mg/L,240 mg/L,360 mg/L and 480 mg/LNa2SO4）.The removal rates of sulfate and Chemical Oxygen Demand（COD）were investigated in IWS-CWs and traditional constructed wetland.Keystone bacteria and dominant bacteria related to carbon and sulfur metabolism in constructed wetlands were also identified.Moreover,The co-occurrence network was analyzed to reveal the microbial metabolism mechanism about the carbon and sulfur.This study provides further insight for the extraction of high-efficiency carbon and sulfur synergistic microorganisms for sulfate wastewater treatment.The results show that:（1）Through the analysis of the microbial community composition of different depth,the microbial diversity was abundant in the soil layers of 5-10 cm and 10-15 cm,while was less in the soil layers of 0-5 cm.The 0-5 cm surface soil was mainly composed of aerobic and photosynthetic microorganisms;The soil depth of 5-10 cm and 10-15 cm were rich in aerobic,facultative anaerobic and anaerobic bacteria related to sulfate reduction,ammonia oxidation,nitrification and carbon source decomposition（e.g.,Desulfobacterales,Desulfuromonadales,Burkholderiaceae and Anaerolineaceae）;The soil layer at 15-20 cm depth was mainly composed of anaerobic bacteria related to C and N metabolism.（2）Based on the analysis of microbial community composition in different seasons,microorganisms related to C metabolism（e.g.,Anaerolineaceae,Rhodobacteraceae and Pseudomona）and S metabolism(e.g.,Desulfobacterales,Desulfuromonadales and Thiobacillus were relatively abundant in spring and fall;In summer,the soil layer was rich in C metabolizing bacteria（e.g.,Anaerolineaceae）and N metabolizing bacteria（e.g.,Rhizobiales,Bacillus and Nitrospiraceae）.Microorganisms in winter soil layer were mainly C metabolizing bacteria,especially those that degrade organic pollutants（e.g.,Sphingomonas）,and N metabolizing microorganisms（e.g.,Nitrospinae）.（3）The dominant microorganisms related to C,N and S metabolism in soil layers in different seasons were closely and complex.The metabolic activities of Sulfate Reducing Bacteria（SRB）not only involve competition among electron donors,but also cooperate with each other to promote sulfate reduction.Moreover,SRB was positively correlated with denitrifying bacteria in systems where SRB was dominant.In the system where SRB and Sulfur Oxidizing Bacteria（SOB）were dominant bacteria,SRB was negatively correlated with denitrifying bacteria.（4）The relationship of sulfate removal rate among the four devices was PA+（60.60%±0.80%）>PA（44.64%±2.72%）>CT+（24.76%±1.76%）>CT（21.73%±2.26%）.The COD removal rate of PA+（73.90%±1.93%）was significantly higher than that of PA（57.94%±1.91%）（P<0.05）.The higher the influent sulfate concentration,the higher the COD removal rate in PA+and PA.Under anaerobic conditions,high sulfate concentrations promote the competition of methanogens with SRB for carbon sources,thereby increasing COD removal.（5）Under high concentration of sulfate stress,the microbial community richness of the planted plant group（PA+and PA）was significantly higher than that of the unplanted plant group（CT+and CT）（P<0.05）.This suggests that plants play an active role in responding to sulfate stress.In addition,microbial community uniformity of PA+was higher than that of PA under different sulfate concentrations.Therefore,IWS was introduced into the constructed wetland as a microbial inoculant to improve the microbial diversity of the plant.（6）IWS,as microbial inoculants,introduced considerable sulfate-reducing bacteria（SRB;Desulfobacteraceae,Desulfobulbaceae,Desulfuromonas and Geobacter）,Sulfur Oxidizing Bacteria（SOB;Ectothiorhodospiraceae,Hyphomicrobiaceae,Rhodoferax,Paracoccus and Thiobacillus）and carbon metabolizing bacteria（Anaerolineaceae,Lysobacter and Pseudomonas）,which improve the sulfur balance in constructed wetland system through sulfate reduction,sulfide oxidation and carbon metabolism.（7）The exchange of matter,energy,and information by microorganisms in PA+and CT+was faster than that in PA and CT.SRB（e.g.,unclassified Desulfuromonadaceae）harbored negative correlations with denitrifying bacteria（e.g.,Thauera,Flavobacterium,and unclassified Burkholderiaceae）because of electron donor competition.However,Flavobacterium and Thauera could cooperate to denitrify through different electron donors to avoid competition.Moreover,Pseudomonas and Amaricoccus had cross-feeding and cooperation in the network when carbon was restricted. |
