Determinantsofsoilcarbonandnitrogenhydrolyzingenzymes.docx

《Determinantsofsoilcarbonandnitrogenhydrolyzingenzymes.docx》由会员分享，可在线阅读，更多相关《Determinantsofsoilcarbonandnitrogenhydrolyzingenzymes.docx（15页珍藏版）》请在课桌文档上搜索。

1、EnvironmentalScienceandPollutionResearchhttpsdoi.org10.17sll356-021-16817-8RESEARCHARTICLEDeterminantsofsoilcarbon-andnitrogen-hydrolyzingenzymeswithindiferentaforestedlandsincentralChinaQianxiLi国 Xiaoli Chengxlcheng Hubei Provincial Academy of Eco-environmental Sciences (Hubei Eco-environmental Eng

2、ineering Assessment Center), Wuhan 430079, Peoples Republic of China* Schl of Environmental Studies. China University of Geosciences, Wuhan 430074, Peoples Republic of ChinaYiranDong2QianZhang, Key Laboratorjf of Soil Ecology and Health in Universities OfYunnan Province. School of Ecology and Enviro

3、nmental Science, Yunnan University, Kunming 650091, Peoples Republic of ChinaWeiJia Key Laboratory of Aquatic Botany and Watershed Ecology. Wuhan Botanical Garden, Chinese Academy of Sciences (CAS), Wuhan 430074, Peoples Republic of ChinaXiaoIiCheng3Received:27May2021/Accepted:25September2021TheAuth

4、or(s),underedusivelicencetoSpringer-VerlagGmbHGermany,partofSpringerNature2021AbstractSoilorganicmatter(SOM)decompositionisregulatedbyacomplexsetofenzymes.However,theinfuencesofbioticandabioticfactorsonspatialvariationsofsoilenzymeactivity(EA)withinecosystemsremainunresolved.Here,wemeasuredEAatdifer

5、entlocationswithintwoaforestedlands(coniferouswoodlandandleguminousshrubland),andsimultaneouslycollecteddataonsoilphysico-chemical,vegetation-related,andmicrobialpropertiestoidentifythedeterminantsofEAspatialpatterns.TheresultsshowedthatsoilorganicCandtotalNcontentswerethepredominantabioticfactorsin

6、regulatingabsoluteEA(EAperunitofoven-drysoilmass)inbothaforestedlands,whilesoilpHwasthepredominantfactorinregulatingspecifcEA(EAperunitofmicrobialbiomass(MB).However,thepredominantbioticfactorsvariedwiththeaforestedtype:therootbiomassandMBwerethedeterminantsofEAintheshrubland,whereasthetreedistribut

7、ion,litterandrootbiomass,andbacterialbiomasswerethedeterminantsinthewoodland.Vegetation-relatedfactors(i.e.,litterandrootbiomass)indirectlyinfuencedsoilEAbyregulatingthesoilabioticfactors.ComparedwiththeMB,microbialcommunitycompositionhadaminorimpactonEA.ThevarianceofspecifcEA(EAperunitofMBorSOM)exp

8、lainedbyselectedfactorswasmuchlowerthanthatofabsoluteEA.Inaddition,theenzymaticC/Nratiowithinecosystemsdidnotfollowageneralpattern(1:1)observedataglobalscale.Ourresultsprovidenovelexperimentalinsightintoecosystem-levelspatialvariabilityofCandNcyclingviaenzymes,suggestingthatsoilabioticfactorsaremore

9、reliablethanbioticfactorstorefectEAspatialpatternsacrossaforestedsystems.KeywordsSoilenzymeactivitySpatialvariationAforestationEnzymestoichiometryVariationpartitioningpublishedonline:26october2021ResponsibleEditor:RobertDuranIntroductionGiventhatsoilscontainthelargestreservoiroforganiccarbon(C)andni

10、trogen(N)inthebiosphere(Lal2004;LehmannandKleber2015),soilorganicmatter(SOM)mineralizationcouldpotentiallyregulateglobalCandNcycling.Meanwhile,soilenzymesareregardedasproximateagentsofSOMmineralizationbecausetheyreducetheactivationenergyofrate-limitingreactionsandspeedupthebreakdownofpolymericmacrom

11、oleculesintolowmolecules(Nannipierietal.2012;Bumsetal.2013;Maoetal.2015).Therefore,accuratepredictionofsoilenzymeactivity(EA)canprovideusefulinformationaboutSOMturnoveraswellasitsresponsetoanthropogenicdisturbancesandenvironmentalchanges(Hanetal.2019).However,thepredictionofsoilEAiscomplicatedsincee

12、nzymesarenotevenlydistributedintheenvironment(Baldrian2014).RelativelyhighspatialvariabilityofsoilEAhasbeenobservedevenwithinasinglefeldbecausesoilEAareregulatedbymultiplebioticfactors(e.g.,vegetationandmicrobialcommunitycomposition)andabioticfactors(e.g.,soilphysico-chemicalpropertiesandmicroclimat

13、e).Inrecentdecades,anumberofstudieshavebeenconductedtoexplorethespatialvariationsofsoilEAandtheirdeterminantsataglobalorregionalscale.Basedonthesestudies,soilpHandSOMcontentwereidentifedasthemostimportantabioticfactorsafectingsoilEA,especiallyforsoilhydrolaseactivity(Sinsabaughetal.2008;KivlinandTre

14、seder2014;Xuetal.2020).However,thespatialvariabilityofsoilEAwithinecosystemshasbeenlargelyneglected(Banerjeeetal.2016;Stursovaetal.2016).Whetherobse,ationsatlargescalescouldapplytoasingleecosystemisstillanopenquestion.AlthoughafewstudieshaveinvestigatedthespatialheterogeneityofsoilEAwithinecosystems

15、andthedeterminants,theseconclusionsareindebate.Forexample,Boeddinghausetal.(2015)reportedthatsoilpHwasanimportantdeterminantofspatialdistributionofEAinagrasslandecosystem,whilestudiesconductedinforestecosystemsandinagrassland-woodlandecotonefoundthatsoilpHwasnotspatiallyconnectedwithsoilEAbecauseoft

16、heverylowvariationsofpHobservedinthesestudies(Banerjeeetal.2016;tursovaetal.2016).Mayoretal.(2016)investigatedthespatialdiferencesinsoilEAlevelsbetweenvegetationpatchesandinter-patchesinashrublandecosystem,andfoundthatvegetationcanopycouldafectsoilEApatternsthroughrhizosphereefectsandsubstrateinputb

17、yIitterfall(Dornbush2007;Brzosteketal.2013;Fengetal.2019).Bycontrast,vegetationpropertiesdidnotSignifcantlyinfuencesoilEAinaforestecosystem(Slursovdetal.2016).Meanwhile,soilmicrobialbiomass(MB)andcommunitycompositionhavebeensuggestedasdirectregulatorsofsoilEAspatialpatternssincetheproductionofaspeci

18、fcenzymeisinducedbysomeparticularspecies(BaldrianandSnajdr2011;Bowlesetal.2014),butexceptionswerealsofoundinotherstudiespartlydueIothatalargeportionofsoilMBwasmetabolicallyinactive(Bocddinghausetal.2015;Stursovdetal.2016).Inaddition,soilpHwasfoundtobecorrelatedwithCellobiohydrolaseandchitinaserather

19、than-and-glucosidasesinagrasslandecosystem.AllthesecontradictoryresultsindicatedthattheefectivenessofbioticandabioticvariablesinregulatingsoilEAwithinecosystemswouldvarydependingontheecosystemtypeorenzymetype.Despiteofthesestudies,onlyfewstudiescomparedtheefectsofsoilphysico-chemicalvariables,vegeta

20、tionproperties,andmicrobialcommunitytogetheronthevariationsofsoilEAwithindiferentecosystems.Moreover,asmultiplefactorsareinterrelated(Walleniusetal.2011),therelativecontributionsofthesefactorstosoilEAspatialpatternshavenotbeenwellinvestigated.SoilEAcanbeexpressedindiferentformsincludingtheabsoluteac

21、tivity(i.e.,activityperunitofoven-drysoilmass)andthespecifcenzymeactivity(i.e.,activityperunitofSOMorMB).ThespecifcEAcanbeusedtoeliminatetheimpactofSOMorMB,andtestwhethervariationsofsoilEAcanoccurindependentlyofvariationsofSOMorMB(RaiesiandBeheshti2014).Todate,muchlessisknownabouthowthespecifcEAresp

22、ondspatiallytootherabioticandbioticfactorsatsmallscaleswithindiferentecosystems.Inaddition,therelativeabundanceofsoilC-andN-hydrolyzingenzymes(i.e.,enzymaticC/Nratio),namely,enzymestoichiometry,exhibitsthepotentialtorefectthebiogeochemicalequilibriumbetweenmicrobialCandNdemandsandnutrientavailabilit

23、yoftheenvironment(Sin-sabaughetal.2009;Mooshammeretal.2014).Thus,spatialvariationsofenzymaticC/NratiowithinecosystemscouldprovideafunctionalassessmentoftherelativeresourcelimitationsofmicrobialmetabolismandtherelativeratesofSOMdecomposition(Sinsabaughetal.2009;Liaoetal.2021).Previousstudiesconcernin

24、genzymestoichiometrypatternshavebeenmainlyconductedatalargeorglobalscale(Sinsabaughetal.2008;PengandWang2016).ThesestudieshaveshownthatratiosofC-andN-hydrolyzingenzymeactivitiesconvergedon1:1.Itislessclearifthepatternofenzymestoichiometryataglobalscalecanbeappliedwithinecosystems.Inthepresentstudy,w

25、einvestigatedspatialvariationsofsoilC-andN-hydrolyzingenzymes(defnedasenzymesthatcontributetothehydrolysisoforganicCandNcompoundsinsoils)withintwotypicalaforestedlands(woodlandandshrubland),aswellasthefactorsthatbestregulatingthesevariations.WehypothesizedthatthespatialvariationsofEAwithinecosystems

26、couldbeexplainedbythecombinationoffactorsrelatedtosoilenvironment,vegetation,andmicrobialcommunity,butthemajordeterminantsofthesevariationswouldVarydependingontheecosystemtypeandenzymetype.Inaddition,toexploretheallocationofC-andN-hydrolyzingenzymes,wealsohypothesizedthattheenzymaticC/Nratiowithinec

27、osystemsshouldbesimilartothatataglobalscale,whichconvergedon1:1.MaterialsandmethodsStudysiteandsamplingdesignThestudywasconductedintheexperimentalareaoftheWulongchiResearchStation(32o45,N,111o13,E),HubeiProvince,China.Primaryforestsinthisregionwereconvertedtocroplandsabout70yearsagoasaresultoftheres

28、ettlementofinhabitants(LiandZhang2008).Largeareasofcroplandswerelaterconvertedtoopenareaswithnovegetationcoverduetointensivelanddegradation.Sincethe1980s,aforestationhavebeenimplementedinthisregion(Zhuetal.2010).Asaresult,mostoftheopenareashavebeenconvertedtowoodlandandshrublandplantations.Thetwoafo

29、restedlandswereunderdifferentnutrientregimes,namely,thatthewoodlandsitewasplantedwithconiferoustrees(Platycladusorientalis(Linn.)Franco,characterizedbyhighC/Nratio),whiletheshrublandsitewasplantedwithleguminousN-fxingshrubs(Sophoradavidii(Franch.)Skeels).Thisdiferenceinlitterqualitybetweenthetwosyst

30、emsresultedindifer-entnutrientregimesanddiferencesinsoilenvironmentandmicrobialcommunity(Table1).Managementsuchasfertilizationandirrigationontheseareashasbeenminimal.BothoftheaforestedsystemsthatdominatedbythetwospeciesalsowidelydistributeinnorthernChina.AstandofIO10mconsistingof22mgridcellswaslaido

31、utineachofthesitesincludingwoodland,shrubland,andtheopenarea(i.e.,control)inApril2017.Surface(0-10cm)soilsamplewascollectedusingacoreaugerateachnodeofthesegrids,resultingin36samplesperstand(Fig.1).Beforesoilsampling,wecompletelycollectedtheabovegroundlitterusinga0.20.2mframeateachnode.Alllivingroots

32、ineachsoilsampleswerecarefullyseparatedfromdeadrootsandwashed.Litlerandlivingrootswereovendriedat65toaconstantweighttoobtainthelitterandlivingrootbiomass(gm2).Allplantsthatlocatedinsideandaroundthe100-m2standwithdiameteratbreastheight(DBH)1cmweremeasured,andtheirgeographiccoordinateswererecorded(Fig

33、.1).SoilanalysisEachfreshsoilsamplewassievedwitha2-mmmesh.Aportionofeachsoilsamplewasfreezedriedforthemeasurementofphospholipidfattyacids(PLFAs),andanotherportionofsoilsampleswerestoredat4forthedeterminationofsoilEAwithin72h.Theremainingsoilswereairdriedforthedeterminationofothersoilproperties.Soilm

34、oisturecontent(SMC)wasobtainedgravimetricallybyOven-drying2()goffreshsoilat105toconstantweight.SoilpHwasmeasuredaftershakingasoil-watersuspension(1:2.5)for30minwithadigitalpHmeter.Soilorganiccarbon(SOC)andtotalnitrogen(STN)concentrationsweredeterminedonanelementalanalyzer(ThermoScientifcFlash2000HT,

35、Germany)afterremovinginorganicmatterbytreatingwith1MHCl(Chengetal.2013).ParameterEcosystem typeWoodlandShrublandCV (%)Open areaMeanCV (%)MeanMeanCV (%)Local environmentsLitter biomass (g m2)823.9a55161.7b94Root biomass (g m 2)560a58139.2b143Soil pH8.1c28.3b38.8a1SMC (%)19.3a2110.8b354.3c22SoilON19.4

36、a2811.5b139.4c16SOC (g kg ,)21.04a416.24b851.29c18STN (gkg-)1.12a380.54b790.14c21RIC (gkg ,)14.99a444.47b651.20c33RIN (g kg l)0.37a410.14b710.10b23Microbial PLFA biomass (nmol g 1 dry soil)Bacterial PLFA74.59a5411.15b656.64c70Fungal PLFA12.33a602.23b731.41c79G* PLFA23.64a573.88b80l.I7c62G PLFA50.57a

37、557.27b595.48c73ACT PLFA14.69a621.73b810.52c65AMF PLFA5.17a620.73b790.19c67Table 1 Mean and coefcients of variation for vegetation, soil, and microbial parameters within each site in the study areaLowercase letters indicate diferences among land types based on an ANOVA with post hoc comparisonsSMC,

38、soil moisture content; SOC, soil organic carbon; STN, soil total nitrogen; RIC, recalcitrance index for C; RIN, recalcitrance index for N: F. total fungi: B. total bacteria; G*, gram-positive bacteria; G-, gram-negative bacteria; AMF, arbuscular mycorrhizal fungi; ACT, actinobacteriaSoilrecalcitrant

39、C(RC)andN(RN)concentrationswereobtainedbyacidhydrolysis(seemoredetailsinXuetal.2015).Briefy,500mgofair-driedsamplewastreatedwith25mlof2.5MH2SO4.Theresiduewasrecoveredbyrepeatedcentrifugation,andthentreatedwith2mlof13MH2SO4overnight.Theremainingresiduewasrecoveredagainasdescribedaboveandthendriedat60

40、Eastin(mlFig.1SoilsamplingschemeandtreedistributioninthethreekindsofecosystemsintheDanjiangkouReservoirarea.Blueasterisksrepresentsoilsamplingsites.RedcirclesintheWoodlandrepresentPlat-ycladusorientalis(Linn.)Franco.RedandgraycirclesintheshrublandrepresentSophoradavidii(Franch.)SkeelsandViiexnegundo

41、L.var.Cannabifolia(SiebetZucc.)Hand.-Mazz.respectively.Thesizeofthecircleinthewoodlandandshrublandisproportionaltotreediameteratbreastheightundshrubbasaldiameter,respectivelyformeasuringRCandRNontheelementalanalyzer.TherecalcitranceindicesforCandN(RICandRIN,respectively)werecalculatedastheratiosofRC

42、andRNtototalCandN.ThemicrobialbiomassandcommunitystructurewereassessedbyusingPLFAanalysis(BossioandScow1998)(seemoredetailsinWuetal.2017).SpecifcPLFAmarkerswereusedtoquantifydiversetaxonomicgroups,includinggram-positivebacteria(G)gram-negativebacteria(G-),actinomycetes(ACT),arbuscularmycorrhizalfung

43、i(AMF),totalfungi(F),andtotalbacteria(B)accordingtoXuetal.(2015)andareshowninTableSl.Amodifedmethodbasedonfuorescent-linkedsubstratemicro-plateprotocolwasusedtomeasuretheactivitiesofenzymes(including-glucosidase(BG),/V-acetyl-glucosaminidase(NAG),andleucineaminopeptidase(LAP)insitupHconditionsandtem

44、perature(Smithelal.2016).Inthepresentstudy,weselectedthesesoilC-andN-hydrolyzingenzymesduetothefollowingreasons:(1)hydrolysishasbeenconsideredmoreimportantthanoxidationinSOMmineralizationprocesses(Nannipierietal.2012),(2)theiractivitiesareusuallymuchhigherthanotherhydrolasesacrossdiferentecosystems(

45、Bowlesetal.2014;Schimeletal.,2017;Zhangetal.2019),and(3)theratioofthethreeenzymes(InBG:ln(NAG+LAP)wasgenerallyusedtorepresentenzymestoichiometry(Sinsabaughetal.2008;PengandWang2016).Inbrief,1gofsoilwashomogeneouslydispersedin90mlofsodiumacetatebufer.ThepHofthebuferwasadjustedto8.0.Thepreparedsoilsus

46、pension,standardsolution,andfuorescentsubstratesolution(200Mintotal)weresuccessivelyaddedintoa96-wellmicroplate(WhatmanInc.,FlorhamPark,NJ).Thecompounds7-amino-4-methyIcoumarin(MUC)and4-methylumbclliferone(MUB)wereusedasthestandardreferencesforLAPandIheremainingenzymes,respectively.Themicroplatewasi

47、ncubatedat25for3.0h,andthen50lof1MNaOHwasaddedtostopthereaction.Thereleasedfuorescencewasdeterminedusingamultifunctionalmicroplatereader(TecanInfniteM200pro,Salzburg,Austria).Thewavelengthofexcitationusedwas360nmandtheemissionusedwas450nm.UnitsforabsoluteEAwereexpressedasnanomolesoffuorescenepergram

48、ofdryfractionperhour.EAwerenormalizedbyMBandSOMtoobtaindifferentspecifcEA(EA:MBandEA:SOM).CalculationandstatisticsWeusedaproximityindex(treeinfuencepotential,IP)toquantifytheinfuenceoftreedistributiononsoilEA(SaetreandB熊th2000).ThisindexrefectsthecombinedinfuenceofneighboringtreesonsoilEAateachsamplingpoint,andisexpressedusingEq.(1):P=iDBHiep(-cdi)(1)whereDBHiisthediameteratbreastheightorbasaldiameterofplantiinmeters,CiSascalingcoefficientandwassett