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Effect Of Nitrapyrin On N2O Emissions And Its Microbial Mechanism In Calcareous Soil

Posted on:2019-02-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:T LiuFull Text:PDF
GTID:1363330566992200Subject:Crop Cultivation and Farming System
Abstract/Summary:PDF Full Text Request
?Object? Nitrification and denitrification losses account for the largest share of nitrogen(N)fertilizer losses in China.N2O,one of the major greenhouse gases(GHG),is generated during nitrification and denitrification and has recently received more and more attention.Thus,how to reduce N losses via soil nitrification and denitrification is a critical research challenge in agro-ecosytems.In calcareous soil,strong nitrification leads to rapid nitrification of nitrogen fertilizer applied,which provides the substrate for denitrification,inducing the denitrification process,finally accelerating the losses of N.The use of nitrification inhibitors(NIs)can inhibit the nitrification process by affecting the activities of ammonia-oxidizing microbes,and slow down the release of available N while reducing N2O emissions,finally increase the nitrogen use efficiency(NUE).Few studies have been undertaken on the influences of different NIs in calcareous soil,information is still scant regarding NIs impacts on N transformation,N2O emissions and even the mechanism of microbes in drip-fertigated calcareous soil in arid region.In this paper,we studied the effect of 2-chloro-6-trichloromethylpyridine(Nitrapyrin),an effective nitrification inhibitor,on soil available N transformation,N2O emissions,and associated soil microbes in drip-fertigated soils of arid region.The purpose is to reveal the microbial mechanism of nitrapyrin affecting N transformation and N2O emissions in calcareous soil,and provide theoretical base and technical approaches to decreasing N losses,thereby promoting efficient utilization of N fertilizer and environmental protection through using nitrapyrin as an additive of urea.?Methods? In this study,a combination of field and simulated experiments using static chamber-GC,Biolog-ECO plate incubation,quantitative real-time PCR and high-throughput sequencing was carried out to study the effect of nitrification inhibitor,nitrapyrin,on N transformation,N2O emissions and associated soil microbes in calcareous soil of the arid region.Three treatments were established:(i)no N fertilizer(CK),(ii)only urea applied(Urea)and(iii)urea plus nitrapyrin at a rate of 1% urea-N(Urea+nitrapyrin),each treatment was replicated three times.?Results? 1.Soil nitrification completed within 7 days after urea fertigation,urea plus nitrapyrin significantly inhibited soil nitrification.In the field trial,soil ammonium nitrogen(NH4+-N)concentration was increased by 25.98% and nitrate nitrogen(NO3--N)concentration was decreased by 11.70% on average after nitrapyrin added compared with urea alone under drip-fertigated condition.In the simulated experiment,nitrapyrin addition increased soil NH4+-N concentration and the ratio of NH4+-N to NO3--N by 233.34%and 316.78% on average,and decreased NO3--N concentration and the apparent nitrification rate by 39.23% and 37.03% on average,respectively.Nitrification was inhibited effectively in 35 days after urea plus nitrapyrin through drip fertigation,nitrification inhibition rates were 6.38-78.48%,with the highest value occurring on the 7th day after incubation.In addition,nitrapyrin addition reduced the amounts of soil mineral N but not significant.2.The application of urea solution greatly stimulated N2O emissions from calcareous soil,while the addition of nitrapyrin exhibited a significant reduction on N-induced N2O emissions compared with Urea.Urea plus nitrapyrin mitigated the cumulative emission(CE)of N2O by 14.28%,reduced emission factor(EF)of N2O by 32.38% in the fertilization season,and increased NUE by 10.70% in the field trial compared with urea only.In the simulated experiment,the addition of nitrapyrin inhibited emission fluxes and cumulative emission amount of N2O by 3.83-77.53% and 51.16%,respectively,and exhibited the strongest effect on inhibiting N2O emissions on the 7th day.The result of field trial showed that there were the significant positive correlations between soil N2O and soil NH4+-N,NO3--N and WFPS,the highest correlation was observed between N2O and NO3--N,followed by WFPS and NH4+-N.WFPS also regulated N2O emissions indirectly through affecting NO3--N.The simulated experiment showed that a significant positive correlation occurred between N2O and soil NO3--N in the critical period of nitrification inhibition.3.The application of urea solution increased the capacity and intensity of carbon metabolism of soil microbes,the diversities and richness of microbial community,as well as the ability of microbial using various types of carbon source compared with CK.The addition of nitrapyrin further increased the capacity and strength of soil microbial carbon metabolism,and the diversities and richness of soil microbial community but not significant compared with urea only.It also improved the utilization of polymers,phenolic acids,carboxylic acids,amino acids and amines,reduced the use of carbohydrates by soil microbes to some extent but not significant.Therefore,nitrapyrin had no significant effects on the total microbial community.The application of urea increased the activities of soil urease,hydroxylamine reductase,nitrite reductase and nitrate reductase compared with CK.Nitrapyrin addition decreased the activities of soil urease and hydroxylamine reductase increased the activities of soil nitrite reductase and nitrate reductase but not significant compared with urea treatment.Significant positive correlations were noted of soil N2O emissions with the activities of urease and hydroxylamine reductase in the field and simulated experiments,with the activities of nitrite reductase in the field experiment,and with the activities of nitrate reductase in the simulated experiment.So,nitrapyrin did not significantly change the activities of key enzymes relate to nitrogen transformation.4.The application of urea increased the gene abundances of soil ammonia-oxidizing bacteria(AOB),ammonia-oxidizing archaea(AOA)and denitrifying bacteria,and changed the community structure of AOB compared with CK.The addition of nitrapyrin significantly decreased amo A gene abundance of AOB and changed the community structure of AOB,it also inhibited the abundance of AOA-amo A gene and changed its community structure but not significant.Nitrapyrin addition decreased nir S,nir K and nos Z gene abundances of denitrifying bacteria,and its inhibition to nir S and nir K was greater than to nos Z.In the field experiment,significant positive correlations were noted of soil N2O emissions with the amo A gene abundances of AOB and AOA.But in the simulated experiment,significant positive correlations were noted of soil N2O emissions not only with the amo A gene abundances of AOB and AOA but also with nir S,nir K and nos Z gene abundances of denitrifying bacteria.Ammonia-oxidizing and denitrifying microbes could be regulated by soil factors such as NH4+-N?NO3--N and WFPS,the result of RDA analysis indicated that soil NO3--N was the most important soil factor impacting on the functional gene abundances of ammonia-oxidizing and denitrifying microbes,and NH4+-N was the most important soil factor impacting on the community structures of AOA and AOB.?Conclusion? Urea plus nitrapyrin added at a rate of 1% urea-N can effectively inhibit soil nitrification and mitigated N2O emissions.Nitrapyrin did not significantly change the metabolic function and diversity of soil microbes,thereby having no significant effects on the total microbial community.It also did not significantly change the activities of key enzymes relate to nitrogen transformation.The addition of nitrapyrin could inhibit amo A abundance of AOB and change its community structure significantly,but had not a significant effect on AOA.Nitrapyrin addition also inhibited the abundance of nir S,nir K,and nos Z of denitrifying bacteria,and the inhibition to nir S and nir K was greater than to nos Z.It can be concluded that nitrapyrin mitigate N2O emissions from nitrification and denitrification processes mainly through changing the abundance and community structure of AOB,and its effect is indirect on the denitrifying microbial and N2O emission from denitrification process.In calcareous soil,NO3--N is the key soil factor regulating nitrifying and denitrifying microbial and N2O emission.
Keywords/Search Tags:Nitrous oxide, nitrifying and denitrifying microbial, ammonium and nitrate nitrogen, nitrapyrin, calcareous soil
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