Analysis On Soil Microbial Flora Changes And Their Driving Factors In Coastal Wetland Of The Yellow River Delta

Soil microorganisms play an important role in all trriestrial ecosystems,which are very sensitive to the environmental changes and can reflect the fertility,health,and restoration of soil.Our study is conducted in the intertidal and supratidal habitats of coastal area in the Yellow River Delta,and the rhizosphere and non-rhizosphere soils in typical halophytic plant communities of Suaeda salsa(S.salsa),Phragmites australis(P.australis)and Tamarix chinensis(T.chinensis)were selected as research objects in this study.The characteristics of soil microorganisms and their enzyme activities in coastal wetlands were studied using an Illumina miseq high throughput16S r RNA sequencing technology.In this research,we hope to find the successional changes of soil microbial diversity,communitie structure,and function in different habitats and different plant communities.Also,soil particle size distribution(PSD),soil organic functional groups and other soil physicochemical properties are combined togather to discuss the main driving factors for soil microbial structure and activity.The results will help us understand the internal mechanism and adaptation strategies of microbial communities in coastal wetland under changing climate conditions,which also provides theoretical basis for management departments to formulate reasonable ecological restoration countermeasures.The main results are as follows:(1)For S.salsa wetlands in different habitats,the OTUs and Shannon index of rhizosphere soil in the intertidal habitat are significantly higher than rhizosphere soil in the supratidal habitat.Proteobacteria and Gemmatimonadetes are the dominant microbial communities at the phylum level in the intertidal habitat.Simultaneously,the microbial genera are dominated by anaerobic and salt-tolerant marine microbes,which include many denitrifying bacteria.The predominant phyla in the supratide habitat are Proteobacteria and Actinobacteria,and charaterised by aerobic and salt-tolerant microbial genus.Among this genus,nitrifying bacteria are common.The PICRUSt prediction results showed that,the dominant metabolic functional microbiota in soils of both habitats are communities with function of amino acid metabolism(AAM),carbohydrate metabolism(CM)and energy metabolism(EM).The results of correlation and redundancy analysis(RDA)indicated that both silt and sand were significantly positively correlated with Shannon diversity index,and the overall distribution of the microbial communities in different habitats were found to be significantly affected by available phosphorus(AP),total potassium(TK),moisture content(MC),available potassium(AK),electrical conductivity(EC),total nitrogen(TN),total carbon(TC),and soil organic matter(SOM).(2)For different halophytic plant communities in the supratidal habitat,T.chinensis community had the largest number of sequencing and Shannon index of soil microbial community.Proteobacteria,Actinobacteria and Chloroflexi are dominant phyla in both rhizosphere soils of P.australis and T.chinensis,and Proteobacteria and Actinobacteria are also prevalent in rhizosphere soil of S.salsa.At the genus level,the unique functional bacteria in rhizosphere soils of S.salsa,P.australis and T.chinensis communities are phosphate-solubilizing bacteria,denitrifying bacteria,and nitrifying and desulfurizing bacteria,respectively.The microbial functional groups in all the three communities are those microbes accociated with AAM,CM and EM.Furthermore,the analysis results showed that the microbial sequencing,OTUs numbers,and all diversity indices were significantly correlated with PSD of silt and sand,and the Shannon index were significantly positively correlated with PSD of clay.In addition,the significant influencing factors of the overall distribution for the main microbial phyla in the rhizosphere soils of different halophytic plant communities are p H,SOM,MC,TC and AK.(3)For S.salsa wetlands in different habitats,soil organic functional groups in the intertidal habitat are dominated by hydrophilic groups,while those in the supratidal habitat are dominated by hydrophobic groups.The overall distribution of soil organic functional groups is significantly affected by soil PSD and physicochemical properties.Moreover,benzene rings,methyl-C,ketone-C,and aromatic-C are the main organic functional groups that affect the overall distribution of major microbial phylum in different habitats.In this study,soil enzyme activities of sucrose(SUC),alkaline phosphatase(AKP),urease(URE),and catalase(CAT)in rhizosphere and non-rhizosphere soils of the two habitats are significantly different.It is indicated by the result that AKP,URE,and CAT are significantly correlated to PSD,EC,SOM,MC,TC,TN,and AK,while SUC is only related to NO₃^--N.Among the soil functional groups,benzene ring,methyl-C,ketone-C,aromatic-C,olefin-C,C-Cl,and?(CO₃^2-)were significantly influence the overall characteristics of soil enzyme activities.(4)For different halophytic plant communities in the supratidal habitat,the contents of fat C and phenolic O-H in T.chinensis community is significantly higher than those in P.australis and S.salsa communities,while the content of Si-O in S.salsa community is the highest.In addition,the overall distribution of soil organic functional groups is significantly affected by PSD and physicochemical properties.Furthermore,those soil organic functional groups can affect the diversity and construction of soil microorganisms.In this study,the activities of SUC,AKP,URE and CAT in soils of the three halophytic plant communities differ significantly.However,only the AKP activitiy show an obvious rhizosphere effect,it is significantly affected by the PSD of silt and sand,and the soil organic functional groups of X-H and O-H.Among the twelve physicochemical properties,the effects of TC,SOM,MC,TN,NH₄⁺-N and EC are significant on the overall distribution of soil enzyme activities in different halophytic plant communities.