Effects Of TiO₂ Nanoparticles On The Nitrogen Transform In Marsh Wetland In Napahai

In recent years,with the rapid development of nanotechnology,the increasing production and application of titanium dioxide nanoparticles(TiO₂NPs)will lead to their release and accumulation in the environment.Owing to that the wetland is located in a relatively lower water catchment environment,TiO₂NPs may enter the wetland ecosystem through multiple pathways,once it enters the wetland ecosystem,it will affect environment and the primary productivity of wetland ecosystem and change the process of soil nitrogen transformation inevitably.However,little is known about the effects and mechanism of TiO₂NPs input on the nitrogen transformation of marsh soil.In this study,the soil of marsh wetland in Napahai was taken as the research object.In order to explore the effects and its mechanism of TiO₂NPs input on soil nitrogen transformation the soil of marsh was collected from field and an indoor cultivated experiment with different addition of TiO₂NPs was conducted.The added concentration of TiO₂NPs was 0 mg·kg^-1(CK),10 mg·kg^-1(A10),100 mg·kg^-1(A100),250 mg·kg^-1(A250)and 1000 mg·kg^-1(A1000),respectively.The soil physiochemical properties,enzyme activities and nitrogen transformation of marsh soil were tested at each experimental treatment.The results showed that with the increase of cultivated period,all TiO₂NPs addition significantly reduced soil physiochemical properties.All TiO₂NPs addition significantly reduced soil p H(p<0.05),TiO₂NPs addition reduced soil total organic carbon(TOC)contents,nitrite nitrogen(NO₂^--N)contents,microbial biomass nitrogen(MBN).All TiO₂NPs addition significantly reduced the total nitrogen(TN)contents after seven and twenty-one days cultivation(p<0.05).With the increase of cultivated period,the effect of TiO₂NPs addition on soil enzyme activities was gradually weakened,TiO₂NPs addition promoted the activity of urease,the treatments of high concentrations significantly reduced the activity of dehydrogenase(p<0.05).the treatments of high concentrations reduced the activity of catalase before thirty-five days cultivation.TiO₂NPs addition promoted the activity of catalase after forty-nine days cultivation,which means that the negative effect of TiO₂NPs addition on the activity of catalase would fade with time.All TiO₂NPs addition promoted the activity of nitrite reductase in initial stage of inhibition,then the trend was opposite,all TiO₂NPs addition promoted the activity of nitric oxide and nitrous oxide.All TiO₂NPs addition did not significantly affect soil ammonization rate,while the treatments of high concentrations inhibited the nitrification rate and mineralization rate,in initial stage of inhibition,then the trend was opposite(p<0.05),which means that soil mineralization was adaptive to TiO₂NPs addition.TiO₂NPs addition reduced soil potential nitrification rate(PNR).Soil nitrogen mineralization rate positively correlated with soil total phosphorus(TP)and nitrate(NO₃^--N)contents,but negatively correlated with NO₂^--N contents,PNR,the activity of catalase and urease.TiO₂NPs addition changed the mineralization process of soil nitrogen by regulating the content of NO₃^--N in marshes.The addition of TiO₂NPs inhibited denitrification rate and promoted N₂O emissions to different degrees.denitrification rate positively correlated with TN contents,but negatively correlated with p H,NO₃^--N contents,MBN and the activity of nitric oxide.N₂O emissions positively correlated with the activity of nitric oxide and nitrous oxide,but negatively correlated with TN contents,TiO₂NPs interfered the denitrification process of marsh soil by affecting soil physiochemical properties,addition of TiO₂NPs improved the N₂O emissions of marsh soil by promoting the activity of the activity of nitric oxide.In conclusion,TiO₂NPs input can affect the global climate change and changing the source and sink functions by affecting environmental factors of wetland nitrogen.