Structural Succession Characteristics And Driving Factors Of Microbial Communities In Coastal Saline Soils Under Organic Fertilization

Coastal saline soils are important reserve resources for sustainable agricultural development.However,high salinity,high pH and low fertility characteristics severely limit the exploitation and utilization of coastal soils.Organic fertilization can enhance the fertility of coastal saline soils and drive the composition and structural reassembly of soil microbial communities,but the characteristics and driving factors of microbial community succession after organic fertilization need further investigation.In this study,the costal saline soils were fertilized,by sewage sludge(S)and sludge-based vermicompost(V)with application rates of 0,50,100 and 200 t ha-1,respectively.Composition and structural diversity of soil bacterial and fungal communities,succession characteristics in core microbiomes over time scales and soil environmental driving factors were investigated at different years(1,2,3 years)after the application of different organic materials,with an attempt to further reveal the evolution characteristics and driving mechanism of bacterial and fungal communities in the saline-alkali soil ecosystem,and provide theoretical basis for obstacle factors remediation and fertility elevation of coastal saline-alkali soils.The main results of the study were as follows:(1)Populations of soil bacteria increased significantly after organic material(S/V)application and tended to increase with application rate and the years after application.Proteobacteria and Bacillus were the dominant bacterial phylum and genus in organic amendments treated soils,respectively.In the S treatments,Shannon diversity index and evenness index of soil bacteria tended to decrease and then increase with the duration of organic fertilization.The relative abundance of Actinobacteria and Gemmatimonadetes showed an increasing trend with increasing S application rate.Core bacterial taxa,such as Desulfuromonadaceae and Bacillaceae,was enriched in the Streated soils,and its relative abundance all gradually decreased with the duration of amendment.Unique taxa belonging to Planctomycetaceae and Anaerolineaceae families appeared only in S-treated soils.In the V treatments,the trends in the soil bacterial Shannon diversity index and evenness index were similar with those in the S treatment.The abundance of Gemmatimonas tended to increase with the amount of V applied.The relative abundance of core bacteria belonging to the Flavobacteriaceae family gradually increased with the duration of the amendment.Unique bacterial groups such as Planctomycetaceae and Geobacteraceae observed only in V-treated soils.The co-occurrence network showed that S and V treatments reduced the size of the soil bacterial community,the degree of mutualism and the stability performance.(2)Populations of soil fungi increased significantly after organic material(S/V)application and tended to increase with application amount and fertilization years.Ascomycota was the dominant fungal phylum in S and V treated soils,and Preussia was the dominant genus in the soils.In the S treatments,Shannon diversity index of soil fungi tended to increase and then decrease with the duration of amendment,while the evenness index tended to increase with the years after organic amendment.Core fungal groups such as Acremonium,Alternaria,Gibberella,etc.,were enriched in the S-treated soil.In the V treatments,Shannon diversity index and the evenness index of soil fungi tended to increase and then decrease with the duration of the improvement.Core fungal families such as Talaromyces and Fusarium were enriched in the V-treated soils,and the relative abundance of Fusarium tending to increase with the duration of the amendment.Compared with CK treatment,S and V treatments showed more modular soil fungal co-occurrence network and weaker positive interaction between species.The structure of the fungal network was more stable than that of the bacterial network.(3)Organic material(S/V)application significantly improved the saline-alkali soil environment.In terms of soil physicochemical properties,pH and salt content tended to decrease with increasing S and V applications rates,while the contents of soil organic carbon(SOC),total phosphorus(TP),total nitrogen(TN),available phosphorus(AP)and alkali hydrolyzed nitrogen(AN)tended to increase gradually.In terms of soil enzyme activity,FDA,sucrase(SUC),urease(URE)and alkaline phosphatase(ALP)activity also increased with the amount of organic material applied.The correlation analysis showed that,in terms of bacteria,pH and salinity were significantly negatively correlated with soil bacterial abundance and Sinobacteraceae in the S and V treatmens,while significantly positively correlated with Desulfuromonadaceae.FDA and SUC were significantly negatively correlated with Desulfuromonadaceae and Ignavibacteriaceae,and significantly positively correlated with Sinobacteraceae.In the case of fungi,pH and salinity were significantly negatively correlated with Fusarium and Mortierella,but positively correlated with Talaromyces in the S treatments.FDA and SUC were significantly positively correlated with Fusarium and negatively correlated with Talaromyces.In the V treatments,Talaromyces showed significant negative correlation with SOC,AN,TN and AP.In addition,fungal populations were positively correlated with SOC,TN,ALP and URE in both S and V treatments,and Shannon diversity and evenness indices were positively correlated with FDA,SUC and TP,while negatively correlated with pH and salinity.The results of the redundancy analysis(RDA)showed that in the S treatments,the main soil environmental factors affecting the structure of the bacterial community were pH,salinity,TP,ALP,FDA and SUC,while for fungal communities were pH,salinity,TN and FDA.In the V treatments,the main environmental factors affecting bacterial community structure were pH,TP,FDA and SUC,the main environmental factors affecting fungal community structure were pH,AN,AP,FDA,ALP and SUC.