Abundance And Diversity Of Ammonia-oxidizing Prokaryotes In Sediments Of East Lake

As the first step in nitrification,ammonia oxidation has always been considered as the key link earth's nitrogen cycle.Ammonia oxidation is carried out by ammonia-oxidizing archaea?AOA?and bacteria?AOB?.Their relative abundance and community structure in the research area determine their relative contributions to the nitrogen cycle.As the second largest urban lake in China,the East Lake has attracted people's attention for its water quality.Although measures for controlling exogenous pollution in the East Lake have been issued in recent years,endogenous pollution is still an important factor in the eutrophication of East Lake.Nitrogen is one of the major nutrients causing eutrophication and endogenous pollutants,and microbes are the engines that drive the nitrogen cycle of lakes.In this study,real-time quantitative PCR technology were used to investigate the abundence of AOA and AOB in sediments from East Lake,and environmental factors affecting their distribution were also analyzed.High-throughput sequencing technology was used to determine the diversity of ammoxidizing microorganisms using 16S rRNA V4 gene as a molecular marker.The aim was to reveal the dynamic changes of ammonia-oxidizing microorganisms between sediments of the sub-lake that represents different nutrient levels in the same lake.We would have a more comprehensive understanding of the eutrophication of freshwater lakes and the production of endogenous pollution.It would provide a theoretical basis for a comprehensive understanding of the effects of nitrogen cycling microorganisms on the lake's endogenous pollution load,it also provided a basis and reference to formulate a lake ecological environment restoration plan.The results were as follows:1.The concentrations of various nutrients in pore water were significantly higher than those in the overlying water and surface water,and the concentrations of TN and NH₄⁺-N in the overlying water were significantly higher than those in the surface water.This indicates that the sediment nutrients of East Lake are releasable in relative to surface water and nitrogen is one of the endogenous pollution.2.The AOA abundance in each sample was significantly higher than that of AOB,and this means that AOA may play a more important role than AOB in the sedimental ammonia oxidation.From the distribution of the season,higher AOA abundance were observed in summer than other seasons in surface and middle sediments?P<0.05?.From the vertical distribution of space,AOA and AOB abundance decreases with depth in different sediments.In most of the sampling sites,the AOA and AOB amoA abundance decreased rapidly along the first 3cm sediment column,and then became stable with the depth increase.This vertical distribution may resulted from dissolved oxygen decrease.From the distribution of different sub-lakes,higher AOA abundance were observed in surface sediment from Guanqiao Lake than others?P<0.05?.Higher AOA abundance were observed in middle sediment from Guozheng Lake than Niuchao Lake?P<0.05?.Correlation analysis showed that AOA abundance were closely related to the concentration of NH₄⁺-N and NO₂^--N in the pore water,while AOB abundance were closely related to the concentration of NO₂^--N.AOA may contribute more to the ammoxidation process of the East Lake sediments.3.The diversity of AOA in surface sediment was higher than that in the deeper layers,while the diversity of AOA was lower than AOB in the East Lake sediments.High-throughput sequencing results showed that 26 AOA OTUs belonging to Nitrososphaera and Nitrosopumilus were detected in all 36 samples and the Nitrososphaera was the dominant population of AOA in East Lake sediments.23 AOB OTUs were identified from the sequencing results,and which belonged to Nitrosospira and Nitrosomonas.The Nitrosomonas lineage was detected in all 36 samples and the Nitrosospira lineage only existed in 26 samples,and the Nitrosomonas was the dominant AOB population in the sediments of the East Lake.Nitrososphaera and Nitrosomonas could be the dominant driver in the ammonia oxidation in the East Lake.