A Preliminary Study On The Changes Of Rhizosphere Soil Microorganisms Of Dominant Plants And Potassium-solubilizing Bacteria In The Three Gorges Drawdown Are

The water-fluctuation zone in the Three Gorges reservoir area has been flooded periodically,resulting in a series of problems such as the reduction of vegetation diversity,soil erosion and so on.It has the characteristics of ecological fragility in the plant-soil-microbial ecosystem.This study starts from the field of plant rhizosphere micro-environment,and explores the dynamic changes of rhizosphere soil micro-environment of vegetation in the Three Gorges water-fluctuation zone after flooding,which is of great significance for understanding the changes of soil environment before and after flooding in the water-fluctuation-zone zone and guiding the restoration of ecology.In this study,the rhizosphere soils of Cynodon dactylon,Xanthium sibiricum,Bidens pilosa of three dominant plants in the water-fluctuation zone of the Three Gorges Reservoir were used as the research object,and the rhizosphere soils of the dominant plants in the none water-fluctuation zone were used as none flooding controls,in order to explore the effects of flooding on the nutrient composition of the rhizosphere soils in the water-fluctuation zone,from which we can understand how to improve soil nutrition and thus better supply plant growth.At the same time,this study explored the diversity of microbial communities in the rhizosphere soil of dominant plants in the water-fluctuation zone through high-throughput sequencing,and screened and identified the potassium solubilizing bacteria that can enhance the potassium nutrition in the reservoir area,so as to further provide a reference basis for improving the soil nutrition in the water-fluctuation zone and repairing the vegetation ecology.The results were as follows:(1)Nutrients were improved after submergence in the rhizosphere soils of dominant plants in the Three Gorges water-fluctuation zone,plants were unable to make full use of nutrients when submerged,nutrients were stacked in the rhizosphere soils of plants,and after submergence,they were conducive to their own adaptation to the environment.The rhizosphere soils of the plants in the Three Gorges water-fluctuation zone experienced flooding of water content,total organic carbon and available nutrients(nitrogen,phosphorus,and potassium)increased;The p H and total carbon content decrease.Flooding had minimal effects on plant of C.dactylon in the water-fluctuation zone,C.dactylon can better achieve nutrient distribution and supply.In addition,the available potassium content is low in the water-fluctuation zone and can be further exploited.After flooding,the activities of invertase,urease,and acid phosphatase in the rhizosphere soil of dominant plants in the water-fluctuation zone increased,and flooding can stimulate the rhizosphere soil microorganisms of dominant plants in the flood zone to stimulate soil enzyme activities.(2)The microbial community structure of the rhizosphere soil of dominant plants in the water-fluctuation zone changed before and after flooding,and the microbial community structure of the rhizosphere soil of dominant plants in the none water-fluctuation zone was relatively stable.After flooding,the relative abundance of Ascomycota in the rhizosphere soil of the three dominant plants in the water-fluctuation zone decreased,while the relative abundance of Basidiomycota and Mortierellomycota increased.Mortierellomycota and Glomeromycota have a strong correlation with soil nutrients and enzyme activities;After flooding,the relative abundance of Proteobacteria and Chloroflexi in the rhizosphere soil of the three dominant plants in the water-fluctuation zone and none water-fluctuation zone increased,while the relative abundance of Actinobacteriota,Acidobacteriota and Firmicutes decreased.The decrease in Firmicutes was caused by Bacillus,which can improve the stress resistance of plants.Therefore,we believe that the introduction of functional Bacillus bacteria after flooding can promote the growth and develo PBent of plants.(3)We screened and identified 22 different strains from the rhizosphere soils in the water-fluctuation zone.A total of 14 strains of potassium solubilizing bacteria have potassium solubilizing ability.The potassium solubilizing rate of each strain is from 0.35%to 12.37%,and the increment of soluble potassium in fermentation broth is from 0.09μg/m L to 2.97 μg/m L.The potassium dissolution rate of PB1 and PB2 belonging to Actinomycetia Arthrobacter were 8.31% and 9.86% respectively,and the increase of soluble potassium were 1.99 μg/m L and 2.37 μg/m L;The potassium dissolution rates of Firmicutes Bacillus PB6,PB7 and PB8 were 7.41%,8.95% and 12.37% respectively,the increase of soluble potassium were 1.78 μg/m L,2.15 μg/m L,2.97 μg/m L respectively;The potassium dissolution rate of PB16 and PB17 of Proteobacteria Acinetobacter were 7.55%and 6.55% respectively,and the increase of soluble potassium were 1.81 μg/m L and 1.57μg/m L respectively.The p H of the fermentation broth of potassium-dissolving bacteria has decreased,but it is not related to the content of soluble potassium.The acid-producing may be the auxiliary solubilization,but it is not the main potassium-dissolving mechanism of these potassium-dissolving bacteria.PB8 has the strongest potassium dissolving ability and belongs to Firmicutes Bacillus,which can be used for ecological vegetation restoration in the the Three Gorges water-fluctuation zone.