Environmental Factors Influencing The Distribution Of Plant Rhizosphere Bacteria In Huixian Wetland Simulation System

Huixian Wetland plays a vital role in purifying water quality,regulating climate and protecting biodiversity as a typical natural karst wetland.However,ecological pollution and degradation have become increasingly serious in recent decades.Plants and rhizosphere microorganisms work together to achieve pollution remediation which also play an important role in maintaining the diversity and purification capacity of wetlands.Highlighting biodiversity was a key measure to improve the purification effect of constructed wetlands.To investigate the relationship between rhizosphere bacterial distribution of different plants and environmental factors and purification effect in simulation wetland system.The Illumina HiSeq 2500 high-throughput sequencing technology was used to sequence and analyze the V4+V5 areas of 16S rDNA gene of rhizosphere bacteria of dominant plants.TP,NH₄⁺-N,TN,COD_Mn have similar degradation rules along the simulated wetland system what thses pollutants were effectively removed in the front 1/3 step,while the latter2/3 step was less effective.The fastest degradation effect was observed along the route in summer,but it was found that syestem also has a function in the latter 2/3 step in winter.Temperature has a great influence on the removal effect of TP,NH₄⁺-N and TN that range from 69.3%～89.1%,62.1%～88.8%,58.3%～81.0%,respectively,however,the removal effect of COD_Mn was smaller（48.3%～59.5%）.The highest purification efficiency of pollutants in sunmmer,followed by autumn and spring,and the winter was the worst.1030524 high-quality effective sequences were obtained in high-throughput sequencing progress and the bacteria were divided into 68 phylums,160 classes,219 orders,391 families,739 genuses and 476 species.The dominant bacterial groups in the rhizosphere soil of different plants were similar,mainly including Proteobacteria（13.7%～59.9%）,Chloroflexi（3.3%～21.6%）,Acidobacteria（1.8%～12.5%）,Bacteroidetes（3.0%～6.6%）,unidentified_Gammaproteobacteria（0.4%～6.8%）,unidentified_Deltaproteobacteria（0.2%～4.9%）,unidentified_Acidobacteria（0.4%～2.8%）,Anaeromyxobacter（0.78%～2.22%）.The bacterial diversity and richness analysis showed that Phragmites australis and Cladium chinense were higher than that of Vallisneria natans and Canna indica.Soil bacterial richness and diversity were the highest in summer,while the diversity and richness was the lowest in autumn and spring,respectively.In comparison,the seasonal variation of bacterial communities in rhizosphere soils of Cannan indica was the greatest,followed by Vallisneria natans and Phragmites australis,the lowest for Cladium chinense.The results showed that the community structure of soil bacteria was more similar in the presence of plants than no plants.Environmental factors have significant impacts on the distribution of rhizosphere bacteria,especially TOC,TN,EP,Pb in soils and water temperature.These were the main cardinal factors for distribution of bacteria and bacterial diversity.TOC and Pb in soils were the core factors influencing the distribution of bacteria in autumn and winter,while water temperature,EP and TN in soils have significant impact in spring and summer.The abundance of denitrifying and dephosphorizing bacteria in the sediment was lower than rhizosphere environment.The denitrifying and dephosphorizing bacteria have the highest abundance of Cannan indica and the lowest of Vallisneria natans,which were higher in summer and autumn than winter and spring.On the whole,the higher OTU number,richness,diversity and the better the purification efficiency.Plants have little function on the main bacterial communities in wetland,but have obvious influence on the species and quantity of bacteria with low abundance.According to the diversity,richness and dominant species of plant rhizosphere bacteria,increasing the cultivation of Phragmites australis and Cladium chinense in Huixian wetland is great significance for maintaining microbial diversity and wetland protection in wetland systems.