Spatio-Temporal Distribution Characteristics And Influen Cing Factors Of Nitrogen Transformation Functional Genes At The Lake Inlet

Excessive nitrogen influx is a major cause of lake eutrophication.Nitrogen can be converted and removed through processes such as nitrification-denitrification,ANAMMOX,and other processes facilitated by microorganisms.Therefore,functional microorganisms involved in the nitrogen conversion process are key to solving nitrogen pollution in lakes.The regulation of the nitrogen transformation process that microorganisms participate in is essentially accomplished by functional genes.The study of nitrogen transformation functional genes using molecular biology techniques can directly explain the characteristics of changes in microbial communities and their potential to participate in nitrogen transformation processes at the nucleic acid level.Nitrogen conversion functional genes play a vital role in the process of nitrogen conversion,and the heterogeneity of environmental factors in different times and spaces leads to changes in the distribution and abundance of these genes.Therefore,it is of great significance to study the correlation between nitrogen transformation functional genes and environmental factors in lake sediments to strengthen the biological denitrification of lakes and to reveal the mechanism of environmental factors affecting the nitrogen transformation process.The study examined the inlets of the Nanfei River,Pai River,and Hangbu River in the Chaohu Lake Basin.Samples of overlying water and sediments were taken during the dry,level,and wet seasons to determine chemical factors such as COD,nitrogen,phosphorus,nutrients,and particle size measures and dissolved organic matter,and analyzed the spatiotemporal variations of environmental factors in the lake estuary.Molecular biology qPCR technology was used to analyze functional genes involved in nitrification,denitrification,ANAMMOX,and nitrogen fixation in the sediments of the lake estuary.The aim was to explore the temporal and spatial distribution characteristics of nitrogen conversion functional genes and to use statistical methods such as principal component analysis and Mantel Test to study the temporal and spatial variation characteristics of the correlation between the abundance of nitrogen transformation functional genes and environmental factors in the lake estuary environment,revealing the main influencing factors of nitrogen transformation functional genes in the lake estuary environment under different time and space conditions.The research results are as follows:（1）Study the spatiotemporal variation of environmental factors in the overlying water and sediments of the lake estuary by means of chemical analysis.The results show that the TN of the overlying water in the three lake inlets has exceeded the standard of Class V water in the dry season,the pollution situation in the level season has been reduced,and the water quality in the wet season is the best.The TN and TP of the sediment showed a rising trend from the dry season to the wet season at times,and the TN of the sediments at the Hangbu River was relatively high in space.The percentage distribution of sediment particle size shows that the sediment particles with a particle size larger than 79.433μm in the Hangbu River during the dry season account for more;The particle size percentage distribution of the Nanfei River and Hangbu River is relatively close in the wet season.The main component of sediment DOM is mainly protein,and the temporal and spatial differences in the proportion of different components are small;while the seasonal variation of the total fluorescence intensity of DOM is obvious,there was a sharp drop in the wet season.The PCA results of environmental factors show that the temporal and spatial differences of the overlying water quality are more obvious.The four indicators of TN,NH₄⁺,COD,and T are the key factors for the division of the temporal and spatial differences of the overlying water in the lake estuary.TP and DOM are the decisive factors of temporal and spatial differences in the sediment environment of the lake estuary.（2）Absolute quantitative analysis of nitrogen conversion functional genes was carried out by molecular biology qPCR.The results showed that the seasonal variation of nitrogen transformation functional genes in the sediment environment of the estuary was relatively obvious,while the spatial variation in the same period was weak.Among the nitrification functional genes,nxr A has the highest abundance,which can reach the order of 10⁹ in the level and wet seasons;the spatio-temporal difference in the abundance of AOB＿amo A is not obvious;the abundance of AOA＿amo A was the highest in the sample points at the Hangbu River during the wet season.Among the denitrification functional genes,the abundance of nar G,nap A,and nir K all showed an increasing trend from the dry season to the wet season;but the abundance of nir S was the highest in the dry season,reaching 10⁸;the abundances of nos Z and nor B both increased significantly during the wet season,reaching6.14×10⁷～1.07×10⁹ and 1.80×10⁵～1.69×10⁶ copies/g,respectively.Among the anammox functional genes,the abundance of hzs A and hzs B showed a similar temporal and spatial variation trend,with the highest values appearing in the Hangbu River during the wet season,reaching 10⁷;the abundance of hzo was always at a low level,at only 10⁴～10⁵.The abundance of the nitrogen fixation gene nif H was about 10⁴ in the dry season,and increased to 10⁶ in the dry and wet seasons.（3）The impact of environmental factors on the abundance of nitrogen transformation functional genes in different time and space was explored by statistical correlation analysis method.The results showed that the main factors affecting the abundance of nitrogen transformation functional genes in the lake estuary environment were different in different time and space.Pearson correlation analysis in the dry season showed that the slightly alkaline p H environment in the three lake inlets restricted the expression of nitrification-denitrification and nitrogen fixation functional genes,and p H was negatively correlated with AOA＿amo A,nir K,nos Z,and nif H.the Pearson correlation analysis in the level season showed that the anammox functional gene was inhibited by environmental factors,hzo and DO showed a significant negative correlation,hzs B and p H showed a negative correlation.The Mantel Test analysis in the wet season showed that the denitrification function gene at the Pai River had a positive correlation with the sediment TP,while the denitrification function gene at the Hangbu River had a positive correlation with the sediment particle size indicators d_0.5 and d_0.9.Figure[27]Table[9]Refer[128]...