Effects Of Simulated Nitrogen Deposition On Bacteria And Ammonia-oxidizing Bacteria In Shuang Tai Estuarine Marsh Sediments

Currently nitrogen deposition causes the estuary ecosystem damage, ecological functiondecreases and other serious problems. In this study, we estimated the effects simulated nitrogendeposition (varied concentrations of urea and nitrogen forms-urea, ammonium sulfate,ammonium nitrate addition, four times) on microbial biomass, bacterial16S rRNA gene content,bacterial community structure, ammonia monooxygenase (amoA) gene content, potentialnitrification rates and ammonia-oxidizing bacteria (AOB) community structure in Shuang taiestuarine marsh sediments in growth area of Suaeda heteroptera for a period of six months,aimed at exploring their response to simulated nitrogen deposition, revealing the effects ofnitrogen deposition on estuarine marsh microbial ecosystems.Microbial biomass carbon (MBC) and biomass nitrogen (MBN) in sediments were measuredby chloroform fumigation after each nitrogen treatment. Results showed that, during nitrogenapplication period, compared to non-treated control group, MBC and MBN in sediments withurea addition of0.1and0.2gN/kg dry soil significantly improved (p <0.01), those with additionof0.4and0.8gN/kg dry soil significantly increased (p <0.05). MBC and MBN in sedimentswith addition of urea, ammonium sulfate and ammonium nitrate (0.2gN/kg dry soil) weredifferent among three nitrogen forms, which significantly higher than those of control group (p <0.05).Content of bacterial16S rRNA gene in sediments was measured using real-time quantitativePCR (real-time PCR) technique after each nitrogen treatment. Results showed that duringnitrogen application period, contents of bacterial16S rRNA gene in sediments with urea additionof0.1,0.2and0.4gN/kg dry soil were significantly improved (p <0.01), those with addition of0.8gN/kg dry soil significantly increased (p <0.05), compared to control group. Contents ofbacterial16S rRNA gene in sediments with addition of urea, ammonium sulfate and ammoniumnitrate three nitrogen forms (0.2gN/kg dry soil) significantly higher than those of control group(p <0.01). Content of bacterial16S rRNA gene in sediments decreased with the increase ofnitrogen application times.Bacterial community structure in sediments was analyzed using denaturing gradient gelelectrophoresis (DGGE) technique after each nitrogen treatment. Results showed that, duringnitrogen application period, addition of varied concentrations of urea had a certain influence onbacterial community structure compared to non-treated control group. No significant differencesin bacterial community structure were observed among urea, ammonium sulfate and ammoniumnitrate three nitrogen forms (0.2gN/kg dry soil) treatments. Proteobacteria is always dominantbacteria of bacteria community during nitrogen application period Diversity of bacteriacommunities in sediments with nitrogen addition were improved, Diversity of bacteria communities in sediments decreased with the increase of nitrogen application times. Thediversity were slightly different among three nitrogen forms.Ammonia monooxygenase (amoA) gene content in sediments was measured using real-timePCR technique after each nitrogen treatment. Results showed that, during nitrogen applicationperiod, contents of amoA gene in sediments with urea addition of0.2gN/kg dry soil weresignificantly improved (p <0.01), those with addition of0.4gN/kg dry soil significantlyincreased (p <0.05), compared to control group. Significant differences were observed amongthe effects of urea, ammonium sulfate and ammonium nitrate three nitrogen forms (0.2gN/kgdry soil) on contents of amoA gene in sediments (p <0.05). Content of amoA gene in sedimentsdecreased with the increase of nitrogen application times.Potential nitrification rate in sediments was estimated by calculating the increase in NO2-and NO3-concentrations from liquid culture with addition NH4+after each nitrogen treatment.Results showed that potential nitrification rates with urea addition of0.1,0.2and0.4gN/kg drysoil were significantly improved (p <0.01) during the period of six months, those with additionof0.8gN/kg dry soil2-4times significantly increased (p <0.05), compared with the controlgroup. potential nitrification rates in sediments with addition of urea, ammonium sulfate andammonium nitrate three nitrogen forms (0.2gN/kg dry soil)2-4times significantly higher thanthose of control group (p <0.01).AOB community structure in sediments was analyzed using DGGE technique after eachnitrogen treatment. Results showed that, during nitrogen application period, compared tonon-treated control group, addition of varied concentrations of urea and urea, ammonium sulfateand ammonium nitrate three nitrogen forms had a certain influence on AOB community structure.There were some differences in AOB community structure among varied concentrations of ureaand urea, ammonium sulfate and ammonium nitrate three nitrogen forms (0.2gN/kg dry soil)treatments. Diversity of AOB communities in sediments with nitrogen addition were improved.Dominant bacteria of AOB transformed from Nitrosospira to Nitrosomonas during nitrogenapplication period.Diversity of AOB communities in sediments decreased with the increase ofnitrogen application times. The diversity of AOB communities were slightly different amongthree nitrogen forms.