| Riparian zone is a key transition area connecting land and water,which is related to the safety of terrestrial ecosystem and water quality.The Three Gorges Reservoir fluctuation area is a special form of riparian zone formed by construction of dam,which reverses the natural water level fluctuation pattern,and the resulting fluctuation area has a drop of up to 30 meters.The new hydrological model of "flood in winter and dry in summer" has seriously affected the soil conditions and vegetation growth in the fluctuation area.Therefore,soil conservation and vegetation restoration have always been the focus of the treatment of the Three Gorges Reservoir.Soil is the substrate for plant growth.Both soil conservation and vegetation restoration are closely related to the development of soil management.Edaphic physicochemical factors are important indicators used to measure soil quality,while soil microorganisms are sensitive indicators indicating soil microenvironment changes.Studying edaphic physicochemical factors and soil microbial diversity in the fluctuation area can clarify the influence of water level fluctuation on soil conditions in the fluctuation area,and provide scientific basis and data support for soil control in the fluctuation area.It provides a new understanding and decision reference for the scientific research and management of soil ecological environment protection in the Three Gorges Reservoir.In the Three Gorges Reservoir,the soil outcropping time is shorter than the inundation time,so vegetation restoration needs to create a condition of rapid growth,and the application of manure can quickly provide nutrients for the growth of plants.However,due to the complex factors affecting the Three Gorges Reservoir,in order to prevent the secondary destruction of the environment,only environmental protection manure can be applied in the Three Gorges Reservoir.Phosphate solubilizing microorganisms have been proved to be an environmentally and friendly manure which can improve the concentration of orthophosphate in soil.The screening of phosphate solubilizing bacteria can provide bacteria resources for the preparation of microbial manure.In this study,soil at different elevations and different trunk and tributaries in the water level fluctuation area(including Ganjing River,Zhuxi River and Pengxi River)in the Zhongxian County to Yunyang section of Three Gorges Reservoir during the water level dry period was taken as the research objects.The spatial variation and correlation of edaphic physicochemical factors and microbial community structure characteristics in the water-level fluctuation area were analyzed,screened and identified phosphate-solubilizing bacteria from soils,and the following conclusions were obtained:(1)The soil is neutral or slightly alkaline,and the soil moisture is negatively correlated with the elevation.There was no significant difference in total nitrogen,total phosphorus and total potassium contents at different elevations.The content of available nutrients(AN,AP and AK)in soil was medium or insufficient.The content of AK was positively correlated with the elevation,while the content of AP was negatively correlated with the elevation.(2)Between 145 and 160 meters,the content of AN in the soil of the tributaries(Ganjing River,Zhuxi River and Pengxi River)was significantly higher than that of the main stream,and the content of AN/TN,AP/TP and AK/TK in the soil of Zhuxi River was higher.In the range of 160 to 175 meters,the AN/TN value of Pengxi River soil was the highest,the AP/TP value of Ganjing River soil was the highest,and the AK/TK value of Zhuxi River soil was the highest.(3)Actinobacteria,Proteobacteria,Acidobacteria,Chloroflexi and Firmicutes were the dominant phyla in soil.The total abundance of the three soil types was greater than 86%,with the highest abundance of Actinobacteria,followed by Proteobacteria.The relative abundance of Actinobacteria and Firmicutes were negatively correlated with elevation,Acidobacteria was positively correlated with elevation.There was no significant change in the relative abundance of Chloroflexi at different elevations.The dominant fungal phyla were Ascomycota,Basidiomycota and Mortierellomycota.The relative abundance of Ascomycota was negatively correlated with elevation.The relative abundance of Mortierellomycota was negatively correlated with elevation.At the bacterial genera level,the abundance of Pseudarthrobacter was the highest,and the dominant fungal genera in the fluctuation area was Talaromyces.(4)At the genera level,Pseudarthrobacter had the highest abundance.TP,AP,p H and SM were positively correlated with the dominant genera in the fluctuation area.Among the environmental factors,SM,p H and AK were the main factors affecting the top 20 bacteria.The effects of AK,SM and p H on bacterial species were negative.In soils with higher SM and p H,the top 20 fungal genera may not have a high requirement for available potassium nutrients.Acremonium,Fusarium,unclassified＿o＿＿Pleosporales,Gibberella,Talaromyces,and Mortierella,these six fungus were not suitable for growth in soil with high soil moisture content and p H.(5)A total of 19 phosphate-solubilizing strains with different functions were isolated from the fluctuation area soil,of which Proteobacteria accounted for 80%.All the calcium phosphate-solubilizing strains belonged to Klebsiella.The strains that mineralized calcium phytate accounted for the largest proportion of Acinetobacter,and the strains that mineralized lecithin accounted for the largest proportion of Pseudomonas.The soluble phosphorus content of Ⅱ-1 and Ⅱ-5 fermentation broth reached about 30 mg/L on the tenth day,which was more than 21 times of that of the control.Class IV strains had the potential to release more soluble phosphorus in later stage.Strain Ⅲ-8 had the most functional genes and showed the most functions. |
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