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Study On The Direct N2 Method And Its Application In Nitrification And Denitrification From Rice Fields

Posted on:2020-11-10Degree:MasterType:Thesis
Country:ChinaCandidate:X Q ZhaoFull Text:PDF
GTID:2393330596493318Subject:Agriculture
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Nitrification and denitrification are important pathways of nitrogen loss and nitrous oxide emission from paddy field;Dry/wet cycle is a key process which affects nitrification and denitrification in paddy soil;During the wet/dry cycle,the redox potential of paddy field fluctuated dramatically,which leads to the enrichment of iron oxides in the rice roots?i.e.,Fe-plaque?.Amorphous iron in Fe-plaque can act as electron donor or acceptor to participate in the nitrification and denitrification processes in paddy soils.The aims of this work were to illustrate the effects of dry/wet cycle on gaseous nitrogen loss and products composition during nitrification and denitrification in a typical paddy soil,using the direct N2 method.The dynamics of key parameters,e.g.nitrate,ammonium and dissolved organic carbon,were monitored to investigate the involved environmental and microbial driving mechanisms during the dry/wet cycle.In addition,the regulatory mechanisms on nitrification and denitrification by Fe plaque are also investigated.The results show:?1?The dinitrogen flux from soils can be directly and accurately determined by the cylinder-in-cylinder setup,which prevented the N2leakage from atmosphere.In this study,the N2 concentration in the headspace of the outer cylinder increased as high as 1400 ppmv with the increasing incubation time.While the N2 concentration in the headspace of the inner cylinder containing autoclaved soil cores stayed consistent and did not exceed 400 ppmv.The cylinder-in-cylinder setup can minimize the leakage rate atmospheric N2 into the incubation vessels and increase the tightness of the whole system.The detection limit of the new method in this study was 5.7?g m-2 h-1,which was low enough to detect the N2 flux released from soil.Moreover,it took 2.5 hours to replace the gas in the soil via new cylinder-in-cylinder setup.It is practicable,time-saving,labor-saving and low cost.Therefore,its application is beneficial.?2?N2 was the dominant product of nitrification and denitrification in paddy soil.The N2 emission rates ranged 0.325.13?mol L-1 h-1 and0.1519.90?mol L-1 h-1 in paddy soil with rice present and absent,respectively.The N2O emission rates ranged 0.130.25?mol L-1 h-1 and0.021.68?mol L-11 h-1 in paddy soil with rice present and absent,respectively.The N2O/?N2O+N2?ratio ranged 0.12%13%and 0.03%37%in paddy soil with rice present and absent,respectively.These results indicated that N2 was the main product and the typical denitrifying bacteria,Pseudomonas,Sulfuritalea and Thiobacillus,was enriched in the flooding period during the dry/wet cycle.These results showed that dry/wet cycle was the hot-moment for nitrogen loss,and the N2O/?N2O+N2?emission ratio from paddy soil increased from wetting to drying,leading to more nitrogen loss by nitrous oxide emission in the soil.?3?Fe-plaque enhanced the nitrogen loss during the dry/wet cycle via Fe???oxidation-coupled denitrification.With Fe plaque present,the N2O production doubled and the abundances of Fe-redox bacteria and denitrifying functional genes were enriched on the root-soil interface,like Thermomonas?Pseudomonas and Thiobacillus.The promoting effect of Fe plaque on N2O emission reappeared under hydroponic conditions when NO3-was the sole N source,but not when NH4+was the sole N source.In addition,scavenging the Fe???on the Fe plaque eliminated the promoting effects of Fe plaque on N2O emission while Fe???addition with the Fe plaque-free roots recovered the N2O emission.These results demonstrate that Fe plaque promotes soil N2O emission and N loss predominately via Fe???oxidation-coupled denitrification.
Keywords/Search Tags:Cylinder-in-cylinder setup, Dry/wet cycle, Soil nitrogen forms and transformation, Fe-plaque, N2O
PDF Full Text Request
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