Nitrification And Denitrification And Diversity Of Functional Bacteria In Sediments Of Liaohe Estuary

Estuary is an important transition zone between terrestrial and marine ecosystems,and also a key channel for terrestrial nutrients to enter the sea.Microorganisms play a very important role in the development of river ecosystem,which is of great significance to the migration and transformation of nitrogen in sediments.It is of great scientific significance to explore the key biochemical processes of nitrification and denitrification in the sediment of Liaohe River Estuary,which are involved by microorganisms,in order to reduce inorganic nitrogen pollution and alleviate eutrophication.Based on this,this paper carried out the following research（1）The nitrification rate and denitrification rate of sediment in Liaohe estuary were determined by mud culture experiment and ¹⁵N isotope labeling technique.The results showed that the nitrification and denitrification rates in September were higher than those in June;There was a significant positive correlation between denitrification rate,heavy metal content and TOC content,but no significant correlation between denitrification rate,environmental factors and heavy metal content.（2）The abundance of functional genes involved in the key processes of nitrification and denitrification in Liaohe estuary sediments was determined by q PCR.The results showed that the abundance of nos Z gene,Napa gene and nor B gene was higher than that of nitrification gene;There was a positive correlation between the abundance of functional genes;The abundance of nxr A gene,nxr B gene,nap A gene and nor B gene had a significant positive correlation with the concentrations of heavy metals and ammonia nitrogen,and a significant negative correlation with the contents of nitrate and do;The abundance of amo A gene,nar G gene and nir K gene was significantly correlated with sediment grain size,and the higher the sand content was,the lower the abundance of functional genes was.（3）amo A gene,nar G gene and nos Z gene were sequenced by high-throughput sequencing technology.The results showed that the dominant strain based on amo A gene was Nitrosospira;The main bacteria with significant difference in different months were Providencia,Faecalibacterium and Nocardia.The main factors affecting the community structure of nitrifying bacteria were sediment particle size,p H and heavy metal ion content.The dominant denitrifying bacteria represented by nar G were Pseudomonas,Serratia and Escherichia;The main bacteria with significant difference in different months were Acidiphilium,Burkholderia,Halomonadaceae and Halomonas.Sediment particle size,NO₃^-content,NO₂^-content,Zn²⁺content and Cd²⁺content were the key factors affecting the community structure of nar G denitrifying bacteria.Thalassococcus,Azospirillum and Leisingera were the dominant bacteria in nos Z denitrifying bacteria community;The species with significant difference in different months are mainly Phreatobacter,Methylobacterium,Woeseia,Roseobacter,Rhodopseudomonas,and the main influencing factors are water depth,PO₄^3-content,NO₂^-content and dissolved oxygen content.（4）There was a significant positive correlation between nitrification rate and abundance of multiple genes,and a significant positive correlation between denitrification rate and abundance of nap A gene.This suggests that the bacteria involved in nitrification and denitrification may contain multiple functional genes of nitrification and denitrification.The diversity of amo A type ammonia oxidizing bacteria was consistent with the change trend of nitrification rate.Denitrification rate,functional gene abundance and community diversity were affected by heavy metal ions in the environment.In conclusion,this study took the Liaohe estuary as the research area to explore the nitrification and denitrification rates,and the bacterial abundance and community structure involved in the key processes of nitrification and denitrification,so as to provide scientific basis for better understanding the key processes of nitrification and denitrification driven by bacteria in the estuary and the pattern of Ocean nitrogen sources and sinks.