Research On The Effect Of Functional Microbes For Nitrogen Transformation Under Different C/N Ratios In Sediment

Nitrogen cycle and transformation is an important energy process within microorganism.Carbon source,as a common electron donor,and nitrogen,as the substrate of nitrogen transformation,both are essential factors in microbial energy process.With the development of industrialization,water environment has been accepting exogenous carbon and nitrogen from sewage,agricultural and industrial waste,changing the original carbon and nitrogen pattern.Researches have shown that changes of carbon and nitrogen conditions would affect microbial community structure and denitrification rates.Therefore,further studies on how C/N ratios effect the nitrogen transformation functional genes would enrich our knowledge of the mechanism of nitrogen biogeochemical cycle.This study,using the sediments sampled in March,2015,from Meiliang Bay,Taihu Lake,with the help of indoor continued-flow incubation experiment,investigated the effect that different C/N ratios have on nitrogen transformation microorganism.The indoor experiment had 2 nitrogen concentrations(2.0 mg·L-1,5.0 mg·L-1),a series of C/N ratios(0.5,2,4,6,10,14),examined the abundance variations of ammonium oxidation and denitrification functional genes in sediments under different C/N ratios,and analyzed the correlation relationship between abundances of nitrogen functional genes and nitrate transformation rates,aimed to investigate how C/N ratios stress on the microbial nitrogen transformation.The main conclusions are as follows:(1)From the experiment results,the background abundances of ammonium oxidation functional genes,AOA-amoA and AOB-amoA in sediment samples are 2.03× 105 copies·g-1 and 1.89 × 103 copies·g-1,respectively.The abundances of ammonium oxidation functional genes are effected by C/N ratios.Ammonium oxidation functional genes decreased along with the increasing C/N ratios,in which,AOA-amoA responded to different C/N ratios more evidently.(2)From the experiment results,the background abundance of denitrification functional genes,nirK and nirS in sediment samples are 1.54×106 copies·g-1 and 2.21× 106 copies·g-1.The results showed that,denitrification functional genes had no significant response to different C/N ratios,in which,along with the increasing C/N ratios,the abundance of nirK has decreased,while the abundance of nirS tend to increase.(3)The experiment results showed that,nitrate concentration in this system is driven by ammonium oxidation and denitrification together.To be specific,nitrate transformation rates significantly negatively correlated to the difference between abundances of denitrification and ammonium oxidation functional genes(r2=-0.612,P<0.01).