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BhattaraiHemRaj*,WanekWolfgang,SiljanenHenriM.P.,RonkainenJussiG.,LiimatainenMaarit,HuYuntao,Nyk?nenHannu,BiasiChristina,MaljanenMarja.Denitrificationisthemajornitrousacidproductionpathwayinborealagriculturalsoils[J].CommunicationsEarthEnvironment,01,(1):54.DOI:10./s-01--7

CommunicationsEarthEnvironment是Nature新子刊，影响因子暂无。

摘要：气态亚硝酸（HONO）光解所产生的羟基自由基是一种关键的大气氧化剂。土壤是HONO的主要排放源，但土壤中HONO的产生路径及其它们的相对贡献却知之甚少。本研究对芬兰的两种农业土壤进行15N示踪实验和同位素库稀释试验，以确定HONO的排放通量和路径。结果表明，对于HONO产生来说，微生物过程比非生物过程更为重要。微生物硝酸盐还原（反硝化作用）远超氨氧化作用作为亚硝酸盐的来源，而亚硝酸盐是与HONO排放相关的主要氮库。在低有机质和高有机质土壤中，反硝化作用分别占总HONO通量的97％和6％。微生物氨氧化作用仅在高有机质土壤中占总HONO排放的10%。本研究结果表明，微生物硝酸盐还原是好氧土壤中一个重要的HONO产生路径，这表明陆地生态系统可能是HONO的排放热点，进而影响大气化学。

Fig.1.The15Natompercentexcess(APE)ofnitrousacid(HONO)andsoilnitrite(NO?)inlabeled15NO?(LNi)andcontroltreatments.The15NenrichedHONOandNO?producedovertime(xaxis)aftertheadditionoflabeled(treatmentLNi;pink)orunlabeledNO?(treatmentcontrol;lightgreen)isshownas15NAPEofHONOandNO?ontheyaxis.Atzeromin,labeled15NO?wasaddedtoincreaseAPEto50%inthelive(a,b)andsterile(c,d)highorganicmattersoils(a,c)andloworganicmattersoils(b,d).Thesquareandtrianglesymbolsindicate15NAPEofHONOandNO?,respectively.Thedatapointsshowthemeanvalues,anderrorbarsdenotestandarddeviation(n=3).Note:theerrorbars,insomecases,aresmallerthanthesizeofthesymbols.StatisticalresultsareshowninSupplementaryTables–3.

Fig..Grosstransformationratesofmineralnitrogenandproductionof15NO?andHO15NOinlivesoils.Grossconsumptionandproductionrates(μgNgdw?1d?1)ofNO?,NO3?,andNH4+inthelivesoilsamplesfromthehigh(HOM;skybluebar)andlow(LOM;turquoisebar)organicmattersoilsareshownonthexaxisofa.aalsoshowsthemaximumbioticHONOemissionratesexpressedinthesameunitsasgrossnitrogentransformationrates.Forclarity,itisshownasaninsetfigure.15NenrichedHONO(squares)andNO?(triangles)productionovertime(xaxis)aftertheadditionof15NH4+(treatmentLA;darkbrown),15NO3?(treatmentLNa;darkorange),andnatural15Nabundance(treatmentcontrol;lightgreen)inthelivesoilsamplesfromtheHOM(b)andLOM(c)soilsareshownas15Natompercentexcess(APE)ofHONOandNO?ontheyaxis.Barsanddatapointsina–cshowthemeanvalues,anderrorbarsdenotestandarddeviation(n=3).Nitrification(F=9.00,P=0.03)andNO3?consumption(F=8.98,P=0.04)ratesweresignificantlyhigherintheHOMsoilthanintheLOMsoil,whichisshownbyasterisks.Theabsenceofanasteriskrighttothebarsinaindicatesnostatisticaldifferenceincorrespondingratesbetweenthesoils.StatisticalresultsforbandcareshowninSupplementaryTables?3.an.d.denotesnotdetected.

Fig.3.Sourcecontributionandnitrousacid(HONO)emissionratesfrombioticandabioticsources.a,cShowthefractionofsourcecontributionsinliveandsterilesoilsamples,respectively,fromthehighorganicmatter(HOM;skyblue)andloworganicmatter(LOM;turquoise)soils.b,dShowthebioticandabioticHONOemissionrates(ngNm?s?1),respectively,inbothsoils.ThesymbolsinaandcindicatetheHONOsources,nitrite(NO?;triangles),sourcesotherthanNO?(emptydiamonds),andunknown(filleddiamonds).Datapointswitherrorbarsina,candfilledareasinbanddshowthemeanvaluesandstandarddeviation(n=3).SourcecontributionstosoilHONOemissionsatand40mininaarethemaximumvaluesfromasinglereplicateinHOMsoil.a–dwerecreatedusingthedatafromtheLNitreatmentoftherespectivesoilsandconditions(seetheMethodssectionfordetails).

Fig.4.Totalsoilnitrousacid(HONO)emissionratesviaabioticandbioticprocesses,withtherelativecontributionofbioticpathwaystoHONOproductionasinset.TotalHONOemissionsrepresenttherateofsoilHONOproductionaveragedover40minutesofHONOfluxmeasurements.TotalHONOproductionrates(ngNm?s?1)forthesoilswithhighorganicmattercontent(HOM,skybluebar)andloworganicmatter(LOM,turquoisebar)areshownontheyaxis.Barsshowthemeanvalues,andtheerrorbarsdenotethestandarddeviation(n=3).Insetshowsthefractionalcontributionofmicrobialammonium(NH4+)oxidation(darkred),nitrate(NO3?)reduction(lightbrickred),andorganicnitrogen(org.N)oxidationtonitrite(purple)pathwaysineachsoil.

Fig.5.Globalsynthesisofsoilnitrousacid(HONO)emissionsrates,grossnitrite(NO?)production,andthecontributionofbioticpathwaystothesoilNO?pool.aShowslog-transformedHONOemissionrates(ngNm?s?1)fromthesoilsofanumberofecosystemsunderdifferentmanagementpractices.Eachyellowboxdenotesinterquartilerange(IQR;5thpercentileatlowerendtothe75thpercentileatupperend)withacentralblacklineasmedian,lowerwhiskerasaminimum(5thpercentile—1.5×IQR),upperwisherasamaximum(75thpercentile+1.5×IQR),andfilledblackcircleasanoutlierofsamplenumberspresentedabovetheboxesofrespectivesoilmanagementpractices.SeeSupplementaryData1formoredetails.Differentlettersinaindicatesignificantdifferencesbetweenmeans(F=.64,P0.05)inHONOemissionsindifferentecosystems.Thecorrelationinbshowstherelationshipbetweengrossnitriteproductionrates(μgNgdw?1d?1)andsoilpHinthisstudy(pinktriangle)andfromsynthesizeddata(lightbrown),i.e.,SupplementaryData.Theslopeinbismarginallysignificant(P0.1),whereastheinterceptissignificantatP0.05.cShowsthepercentage(%)contributionofdifferentbioticpathways,organicnitrogenoxidation(whitebar),nitrification(lightgraybar),denitrification(darkgraybar),andratioofdenitrificationtosumofnitrificationanddenitrification(blackbar)tothesoilNO?pool.SeeSupplementaryDataformoredetails.

Fig.6.Conceptualmodelshowingnitrousacid(HONO)productionpathwaysassociatedwiththenitrogencycleinagriculturalsoils.PathwaysassociatedwithHONOproductionareindicatedwithsolidcoloredarrowsandaredefinedatthebottomleftofthefigure.Pathwaysthatareyettobeconfirmed(e.g.,NHOH+HOandDNRA)orhavingpotentialbutwerenotstudiedyet,i.e.,chemo-denitrificationconcerningHONOproductioninsoils,areindicatedbydottedcoloredarrowsandwithquestionmarks(?).Chemo-denitrificationisaprocessassociatedwiththeabioticreactionofnitriteornitrateinthepresenceofamines,reducedmetals(e.g.,Fe+),andhighsoilorganiccarbontogaseousnitrogenforms.Arrowsdenotingdenitrificationarethickest,indicatingdenitrificationtobethemostsignificantpathwayofHONOproductionviathesoilnitrite(NO?)poolinsoilswithpH7.Thisconceptualmodelisbasedonfindingshere,andliteraturespublishedearlier.

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