homogeneitytokyohotn0717

ContentslistsavailableatScienceDirectJournalofEnvironmentalManagementjournalhomepage:www.
elsevier.
com/locate/jenvmanResearcharticleVegetationrestorationdrivesthedynamicsanddistributionofnitrogenandphosphorouspoolsinatemperatedesertsoil-plantsystemYanghaotian,Wangzengru,Lixiaojun,GaoyanhongShapotouDesertResearchandExperimentStation,NorthwestInstituteofEco-environmentandResources,ChineseAcademyofSciences,Lanzhou730000,ChinaARTICLEINFOKeywords:NitrogenpoolPhosphorouspoolDistributionpatternsVegetationrestorationRestorationseriesABSTRACTTherolevegetationrestorationandsuccessionplayinregulatingNitrogen(N)andPhosphorous(P)poolsre-mainsunexploredandpoorlyunderstood.
Toexaminetheeectsofvegetationrestorationandsuccessionfromashiftingsanddunetorestoredvegetationatdierentages(23,33,50,and58years)onthedynamicsanddistributionofNandPpoolsinasoil-plantsystem,acomprehensiveeldinvestigationwasconductedandN(P)concentrationsanddensitiesofsoil,shrubs(includingleaves,newbranches,agingbranches,androots),andgrass(includingaboveground,roots,andlitter)ateachsitewereanalyzedandquantied.
WefoundthattotalN(TN)andtotalP(TP)densityfortheplant-soilsystem,inliveshrubbiomassaswellassoilTN(STN)densityinsubsoil(10–100cm),decreasedbetween23and50years,andthenincreasedfrom50to58years.
STNandsoilTP(STP)densitiesintopsoil(0–10cm),andNandPdensitiesofherbageanddeadshrubs,continuedtoincreasewithrestoration.
NandPwereprimarilystoredinsoilsandaccountedfor89.
83%–92.
06%and99.
33%–99.
48%oftheTNandTPpools,respectively.
Intherst23years,liveshrubsmadeupthesecondlargestNandPpools,however,herbagemadeupthesecondlargestNandPpoolsafter23years.
TheratiosofNandPinherbagetoTNandTPdensityincreasedfrom3.
71%to6.
31%,and0.
33%–0.
43%,graduallyapproachingthenativesite(6.
39%and0.
46%).
TheratiosofNandPinliveshrubstoTNandTPdensityinthesoil-plantsystemdecreasedfrom4.
55%to1.
08%andfrom0.
33%to0.
13%.
OurresultsindicatedthattherestoredecosystemwasaN(P)sourcefrom0to50(0–23)years,andaN(P)sinkfrom50to58(23–58)years,withstrongpotentialforaccumulatingmoreN(147.
18gm2)andP(102.
67gm2)toreachthenaturalsitelevels.
TheseresultssuggestthatvegetationrestorationandsuccessionmayprofoundlyalterNandPgeochemicalcyclesthroughN(P)re-distributioninatemperatedesertplant-soilsystem.
ProperNandPadditionattheinitialstageofvegetationrestorationmaypromotetherecoveryofdesertiedland.
1.
IntroductionNitrogen(N)andphosphorus(P)aretwoofthemostimportantnutrientsforalllivingorganisms.
Theyarekeycomponentsofaminoandnucleicacidsandcannotbereplacedinmostbiologicalfunctions(MarschnerandRengel,2007).
Thealterationofthesetwoelementshasthepotentialtoprofoundlyaectecosystemstructure,function,andkeyecologicalprocesses,suchasplantgrowth,communitystructure,speciesdiversity,netprimaryproductivity,andglobalcarboncycles(VitousekandHowarth,1991;GruberandGalloway,2008;XiaandWan,2008;Yuetal.
,2010;Vitouseketal.
,2010).
NandParelimitingnutrientsinmanyterrestrialecosystems,especiallydeserts(CrawfordandGosz,1982;SchlesingerandRaikes,1996;Elseretal.
,2007;LebauerandTreseder,2008).
Hence,theirdynamicsareconsideredtobeimportantfactorsintheassessmentofthebiologicalandbiogeochemicalstatesofterrestrialecosystems.
Nutrientsarealwayscyclingamongvariouspoolsinanecosystem.
Desertecosystemscoverapproximately20%oftheearth'slandsurface(Whitford,2002),andthemostimportantnutrientpoolsincludesoil,liveshrubs,deadshrubs,livegrass,andlitter.
Identifyingandquanti-fyingthedynamicsofallpoolsinasoil-plantsystemcanprovidein-sightsintogeochemicalandbiologicalprocessesandplayanimportantroleindesertecosystemmanagement(Delgado-Baquerizoetal.
,2013).
Consideringthehighspatialheterogeneityofnutrientsinaridregionsandalackoflong-termexperimentalconditionswithoutexternalin-terference,theremaybegreateruncertaintyabouttheestimationofNandPindrylandecosystems(Hartleyetal.
,2007).
TherehavebeenextensivestudiesonNandPcontent,pools,inputs,mineralization,andsoilloss(Fengetal.
,2016),butfewonthedynamicsofNandPpoolsinsoil-plantsystems.
Toreducethisuncertainty,amoreaccuratehttps://doi.
org/10.
1016/j.
jenvman.
2019.
04.
108Received25October2018;Receivedinrevisedform14April2019;Accepted25April2019Correspondingauthor.
DonggangWestRoad320,Lanzhou730000,Gansu,China.
E-mailaddresses:yanghaotian6516@163.
com(Y.
haotian),surgeriver@gmail.
com(W.
zengru).
JournalofEnvironmentalManagement245(2019)200–2090301-4797/2019PublishedbyElsevierLtd.
TevaluationofindividualpoolsandNandPdynamicsinsoil-plantsys-temsunderdierentclimateconditionsisneeded.
NutrientpoolsinplantorgansplaycriticalrolesinNandPtransportandproteinsynthesis(Nordinetal.
,2001).
ThedynamicsofNandPpoolsaredirectlyrelatedtotheamountofplantbiomassandtheche-micalcompositionofplanttissue(Vitouseketal.
,1987).
ThesupplyofNandPisprimarilybasedontheamountandturnoverratesofplantbiomass,whichareverylowindesertareasduetolowprecipitationandhightemperatures(Noy-Meir,1985).
Desertplantshaveevolvedtohavemanynutrientconservationstrategies,suchaslowgrowthrates,increasedphysiologicaluptakecapacity,nutrientrecyclingandstorage,andalonggreentissuelifespan(Jacksonetal.
,1990;DrenovskyandRichards,2006).
ThedierentplantcomponentsmaybeessentialtoNandPcyclingduetotheirdramaticallydierentsurvivaltimesanddecompositionrates(Strojanetal.
,1979;YangandPost,2011).
Therefore,perennialdesertplantswithvariousorgansmayplayanimportantroleinregulatingNandPstorageandcyclingindeserts(CrossandSchlesinger,1999).
Theabilityofanecosystemtoaccumulatenutrientsisdependentonmanagement.
Humanactivitiesareimportantfactorsthatdirectlyorindirectlyalterthemovementanddistributionofnutrientswithinoramongpools,modifyingcommunitycompositionandecosystemfunc-tion(Schnabeletal.
,2000;Lüetal.
,2013).
Previousstudieshavein-dicatedthatgrasslanddegradationoftenresultsinthelossofsoilnu-trients(Hughesetal.
,2002).
Inaddition,vegetationsuccessionisanimportantfactorfornutrientpoolsanddynamics(WalkerandSyers,1976;Fisketal.
,2002;YangandPost,2011).
However,knowledgeisstilllimitedabouttheeectsofvegetationandsoilsuccessiononNandPdistributionanddynamicsinrestoreddesertecosystems.
ToprovideinsightsintoNandPcyclingindesertecosystems,itisthereforene-cessarytoimproveourunderstandingofNandPpoolsandhowtheyareaectedbylandmanagementpracticesandsuccession.
AnextensivevegetationrestorationprojectwasimplementedbytheChinesegovernmenttoprotectsoils,mitigatedesertication,preventandcombatsandstormsandsandduneburial,andimproveecosystemresilienceindesertlands(Lietal.
,2006).
XerophyticshrubssuchasArtemisiaordosicaKrasch,CaraganakorshinskiiKom.
,andHedysarumscopariumFischwerefoundtobethemostsuitablespeciestostabilizeshiftingsanddunesaftertheestablishmentofstrawbarriersalongtransportationroutes,pipelinecorridors,andpowertransmissionlinesinplaceswithlimitedprecipitation(2mm(Batjes,1996).
NandPdensitiesoftheabovegroundbiomassforeachshrubspeciesweredeterminedaccordingtoEq.
(2):∑=MSANDn(SAPDn)(kgm)N(P)i2iki(2)wherenrepresentstheshrubspecies,SANDn(SAPDn)isN(P)densityoftheabovegroundbiomassfordierentshrubspecies,krepresentsthedierentfractionsofabovegroundshrubbiomass,N(P)iistheTN(P)content(%)offractioni,andMiisthebiomass(kgm2)offractioni.
Consequently,thetotaldensityforabovegroundNandP(SANDandSAPD)forallshrubspeciescombinedwascalculatedusingEq.
(3):∑=SAPDnSAND(SAPD)(kgm)SANDn()nm2(3)wheremrepresentsthenumberofshrubspecies.
NandPdensities(SRNDandSRPD)fortheshrubrootswerecal-culatedusingEq.
(4):∑=MSRND(SRPD)(kgm)N(P)n2nmn(4)wheremrepresentsthenumberofshrubspecies,N(P)nistheN(P)content(%)ofarootfromspeciesnandMnistherootbiomass(kgm2)ofspeciesn.
GAND(GAPD)representstheN(P)densityofabovegroundherbage:Y.
haotian,etal.
JournalofEnvironmentalManagement245(2019)200–209202=*GAND(GAPD)(kgm)N(P)M2(5)whereN(P)representstheN(P)content(%)ofherbageandMistheabovegroundbiomass(kgm2)ofherbageineach1m*1mplot.
NandPdensities(GRNDandGRPD)oftheherbagerootswerecalculatedbyEq.
(6):∑=NPMGRND(GRPD)(kgm)()nii2i(6)wherenisthenumberoflayers,N(P)iistheN(P)content(%)oftheherbagerootsinlayeri,andMiistherootbiomass(kgm2)oflayeri.
AllindividualcomponentsweresummedtoobtainTNandPden-sities(TNandTP)foreachsite.
2.
8.
StatisticalanalysesThedatafromeachsiteweretestedforhomogeneityofvariance(usingLevene'stest)andthenormaldistribution.
Analysisofvariance(ANOVA)wasusedtoquantifydierencesinSTN(STP)atdierentsoildepths,STN(STP)density,NandPdensitiesamongshrubcomponents,andNandPdensitiesinherbageacrossthesixsites.
Tukey'stestwasappliedposthoctodistinguishbetweenthemeansatdierentsites.
Thesignicancelevelwassetto0.
05foralltests.
AlldatawereanalyzedusingSPSSsoftwareversion15.
0(SPSS,Chicago,IL,USA).
3.
Results3.
1.
SoiltotalnitrogenandphosphorusconcentrationsSandrepresentstheshiftingdunesite;58-year,50-year,33-year,and23-yearlabelsrepresentsand-bindingvegetationsitesthatwereestablishedin1956,1964,1981,and1991,respectively.
Nativere-presentsthenativedesertsteppesitewithnativevegetation.
Valuesareexpressedasmean±SE.
STNconcentrationsvariedlittleatdierentdepthsinthesandsite(P>0.
05).
STNvaluesatrestoredvegetationsites(23-,33-,50-and58-year)graduallydeclinedfromthesurfacetothedeepestlayer.
The0–5cmand5–10cmsoillayerscontainedsignicantlyhigherSTNconcentrationsthanotherdeepersoillayers(P0.
05).
Onlythe10–30cmsoillayercontainedsignicantlyhigherSTNconcentrationsthanotherdeeperlayersatthe33-yearsite(P0.
05)(Fig.
2A).
TherewasasignicantincreaseinSTPconcentrationsfromthesurfacetothelowerlayersofthesandsite(P0.
05)at23-year,50-yearand58-yearsites,orbetweensoillayerslessthan30cm(P>0.
05)at33-yearsite.
Therewerenosig-nicantdierencesbetweenthelayersatthenativesite(P>0.
05)(Fig.
2B).
3.
2.
STNandSTPdensityFortopsoilwithrestoredvegetationsuccession,STNandSTPden-sitiesincreasedsignicantlycomparedtonativevegetationafter33years.
Comparedwiththesandsite,STNandSTPdensitiesatthe58-yearsiteincreasedby2.
137and1.
083times,respectively.
Thereweresignicantdierencesbetweendierentrestoredsites.
Inaddition,STNandSTPdensitiesatthe58-yearsiteweresignicantlygreaterthanthenativesite(Fig.
3).
Forsubsoil,STNdensityrstdecreasedsignicantly(P0.
05),buttheyweresignicantlyhigherthanthe23-yearand33-yearsites(P0.
05)(Fig.
4CandD,E,F).
NandPdensitiesattherestoredsitesweresignicantlylowerthanthatatthenativesite(P<0.
05).
3.
4.
NandPdensitiesinshrubbiomassNandPdensitiesofallliveshrubcomponentsreachedmaximumvalues23yearsaftertherestoredvegetationwasestablished(Figs.
5and6).
Therewerealsosharpdecreasesbetween23and50years,reachingaminimum,butNandPdensityvaluesincreasedagainfrom50to58years.
Atthatpoint,NandPdensitieswereindistinguishablefromthenativevegetationsite(Figs.
5and6).
Dierencesbetweenthe23-and50-yearsitesweresignicantbuttherewerenosignicantdierencesbetweentheothersites.
3.
5.
NandPdensitiesofdeadshrubbiomassNdensityofabovegroundandrootbiomassofdeadshrubsin-creasedwithvegetationsuccessionandreachedamaximumatthe58-yearsite.
Thiswassignicantlyhigherthantheotherrestoredsites(P<0.
05).
Pdensityofdeadshrubbiomassincreasedsignicantlyafterrestoredvegetationestablishment,reachingamaximumatthe58-yearsite.
Thiswassignicantlyhigherthan23and33-yearsitesandthenativesite.
Pdensityofrootbiomassincreasedgraduallywiththeve-getationsuccessionandthedierencebetweenrestoredsiteswasnotsignicant,buttheseweresignicantlylowerthanthenativesite(Fig.
7).
3.
6.
TNandTPdensitiesTNdensityoftheplant-soilsystemrstdecreasedsignicantly(P<0.
05)andreacheditslowestvalueafter50years,beforesignicantlyincreasingagain(P<0.
05).
TPdensitysignicantlydecreasedandreachedthelowestvaluesatthe23-yearsite(P<0.
05).
However,TPdensityincreasedsignicantlywiththesuccessionofrestoredvegeta-tionfromthe23–58-yearsites(P<0.
05).
Ingeneral,TNandTPden-sitiesofrestoredsitesweresignicantlylessthanthoseofthenativesite(P<0.
05)(Fig.
8AandB).
TheaverageannualratesofchangeinTNandTPdensityweredierentacrossthefoursuccessionalstages(Fig.
8CandD).
3.
7.
NandPdensitydistributioncharacteristicsTheestablishmentofrestoredvegetationsignicantlyalteredtheNandPdensitydistributionscomparedwiththeshiftingsanddunesite.
Withvegetationsuccession,theNandPdensitydistributionsbecamesimilartothenativesite.
BothNandPweremainlystoredinthesoil.
STNdensityaccountedforabout90%ofTNdensity(Appendix,TableS1)andSTPdensityaccountedfor99.
40%ofTPdensity(Appendix,TableS2).
Forherbage,theNandPdensityratiosinrestoredvegetationY.
haotian,etal.
JournalofEnvironmentalManagement245(2019)200–209203graduallyincreasedandreachedmaximumvaluesof7.
16%and0.
42%atthe50-yearsite.
Afterthat,thePratiodidnotchangebuttheNratiodecreasedto6.
14%,whichwassimilartothenativesite.
Forliveshrubs,theNandPdensityratioswererelativelyhighatthe23-yearsite,reaching4.
55%and0.
32%.
Withvegetationsuccession,theratiograduallydecreasedandreachedminimumvaluesof1.
07%and0.
06%atthe50-yearsite,andthenincreasedto1.
97%and0.
13%toexceedthevaluesatthenativesite.
Fordeadshrubs,theNandPdensityratiosgraduallyincreasedwiththesuccessionofrestoredvegetation.
TheNdensityratioduringearlysuccession(23-yearsite)wassimilartothenativesite,whileratioslaterintosuccessionwasgreaterthanthenativesite.
Forlitter,theNandPdensityratiosgraduallyincreasedwiththesuccessionofrestoredvegetation(Appendix,TablesS1andS2).
4.
Discussion4.
1.
SoiltotalNandPOurresultsshowedsignicantchangesinthespatialandtemporaldistributionsofNandPconcentrationsinthesoilprole.
TheseNandPdynamicscouldbeexplainedbythefollowingreasons.
Fortopsoil,theNandPinputsmayhavebeengreaterthanthelosses.
First,thecov-erageandproductivityofshrubsandherbageincreasedsignicantlyaftertheestablishmentofrestoredvegetation(Lietal.
,2004;Yangetal.
,2014),becauselitterfromshrubs,herbage,anddeadshrubsisanimportantnutrientsourcefortopsoil.
Second,biologicalsoilcrusts(BSCs)colonizedandbecamewelldevelopedoncethemobilesandduneswerestabilized(Lietal.
,2003).
NumerousN2-xingcyano-bacteriaspecieslivingwithinBSCs,includingNostoc,Scytonema,andSchizothrix,increasedthenitrogenxationcapacityoftopsoil(Li,2012).
Third,wetordrydepositionwasanothermajornutrientinputsource(MarschnerandRengel,2007)andthecolonizationofBSCsal-teredthetexture,roughness,andporosityofthesoilsurfacetoenhanceitsabilitytocaptureatmosphericdust(Warren,2001).
Fourth,mostherbagenerootswereinthe0–10cmsoillayer;therefore,rootturnover,rootexudation,andne-rootmortalityalsoincreasedsoilnutrients(Kalbitzetal.
,2003).
Fifth,rootsandBSCssignicantlyin-creasedsoilmicrobialbiomass,communitydiversity,andactivityinthe0–20cmsoillayer,whichmediatedthedecompositionoforganicmatter.
Atthesametimethesemicrobialattributesdecreasedsig-nicantlywithsoildepthandincreasedwithcrustage(Liuetal.
,2013,2017).
Inaddition,protectingrestoredvegetationfromgrazingandotherhumanactivitieswasanimportantfactorpromotingtopsoil(0–10cm)restoration.
Basedontheabovefactors,topsoilwaswellrestoredwiththesuccessionofvegetation.
Moreleguminousshrubswerefoundintherestoredvegetationthatfurtherenhancedbiologicalxation,sotheSTNandSTPvaluesoftopsoilexceededthoseinthenativevegetationsite.
ThechangeinSTNandSTPinsubsoilwasop-positetothatoftopsoil.
ThiswasmainlybecauseNandPindeepsoillayerswereabsorbedandutilizedbyalargenumberofdeeprootedshrubsduringtheearlystages.
SomenutrientsweretransferredtoandFig.
2.
TheverticaldistributionsofSTNandSTPwithsoildepth.
Fig.
3.
STNandSTPdensityoftopsoilandsubsoilatdierentstudysites.
Valuesaremean±SE.
Lettersindicatesignicantdierencesbetweensites(P<0.
05).
Y.
haotian,etal.
JournalofEnvironmentalManagement245(2019)200–209204storedindierentcomponentsofshrubbiomass(mainlynewbranches,agingbranches,shrubroots,anddeadshrubs),andothersweretrans-ferredtothetopsoilthroughlitter.
Nutrientswerepresentinlowquantitiesinsandysoilsandthemainsourceofphosphorouswastheweatheringofprimaryminerals(LajthaandSchlesinger,1988;Newman,1995).
Inaddition,nutrientsstoredindeepsoilwerenoteectivelysupplementedinotherways.
Ingeneral,woodyplantspeciesdeterminethequalityandquantityoforganicmatterinputsandmicrobialcommunities(Landietal.
,2006).
Withthesuccessionofvegetation,shrubcoverage,composition,andsoilmoisturedecreasedsignicantlytostablelevels(Lietal.
,2004;Yangetal.
,2014),sothatbythelatestageofsuccessiontherewaslittlevariabilityinsubsoilSTNandSTP.
MoststudiesonNandPhavebeenlimitedtotopsoil,basedontheFig.
4.
NandPdensitiesof(A,B)roots,(C,D)livingbiomass,and(E,F)litterbiomassforherbageatrestoredsitesandthenativevegetationsite.
Valuesareexpressedasmean±SE.
Lettersindicatesignicantdierencesbetweensites(P<0.
05).
Fig.
5.
Ndensityof(A)liveshrubleaves,(B)newbranches,(C)agingbranches,and(D)shrubrootbiomassatthesand-bindingvegetationsitesandthenativevegetationsite.
Valuesareexpressedasmean±SE.
Lettersindicatesignicantdierencesbetweensites(P<0.
05).
Y.
haotian,etal.
JournalofEnvironmentalManagement245(2019)200–209205assumptionthatland-usechangeonlyaectsthislayer(Zhangetal.
,2006).
Asaresult,verylittleisknownaboutthedistributionofNandPcontentandpoolsthroughoutthesoilproleof0–100cm(Burtonetal.
,2007).
Inthepresentstudy,ourresultsindicatedthattheconversionofshiftingsanddunestorestoredvegetationgenerallyalteredSTNandSTPdensities,notonlyinthetopsoil,butalsointhedeepersoilprole(10–100cm).
TheresultsshowedthatSTNandSTPdensitiesintopsoilrangedfrom16.
13gm2(atthesandsite)to50.
61gm2(atthe58-yearsite)andfrom20.
87gm2to43.
47gm2acrossfourstagesofsuccessionwithdierentaverageannualsequestrationrates.
Thiswasconsistentwithotherstudiesthatfoundthatland-usechangesignicantlyalteredNandPpoolsintopsoil(Burtonetal.
,2007).
However,thereweresignicantdeclinesinSTNandSTPdensitiesinthesubsoilduringtheearlystagesofsuccession,butnutrientsweresequesteredduringthelatestageswithvaryingannualaveragelossesorsequestrationrates.
Consideringthattheprocessesofsoilformationorrestorationareveryslow(Lietal.
,2007),STNandSTPdensitiesinthesubsoilofrestoredvegetationsiteswerefarlowerthanthenativesite.
ThismeansthatthesubsoilinrestoredvegetationhadalargerpotentialforNandPstorage.
Inconclusion,ourresearchshowedthatsubsoil,inadditiontotopsoil,hadimportantimpactsonSTNandSTPpoolsandinterannualvaria-bility.
4.
2.
NandPdensitiesinplantbiomassNandParetwobiologicallyessentialelementsthatconstrainplantgrowthandarethemostabundantelementsfoundinplantdrybiomass(Elseretal.
,2007).
OurndingsdemonstratedthatNandPdensitiesinplantbiomasswerehighlyresponsivetothechangefromshiftingsanddunestorestoredvegetation.
Intherst23years,thecover,pro-ductivity,andbiomassofliveshrubsattherestoredsitesreachedmaximumvegetationcarryingcapacityandshrubdeathoccurredatalowerrate(Lietal.
,2004;Yangetal.
,2014).
Asaresult,NandPdensitiesinliveshrubsreachedamaximumandwerelowerindeadshrubbiomass.
Twenty-threeto50yearsafterestablishment,themoisturecontentofthedeepersoillayerscontinuedtodecrease,causingvegetationcoverandproductivitytodecrease.
Themortalityofliveshrubswithdeeprootsystemsincreasedduetotherestrictedwaterconditions(Lietal.
,2004).
Duringthisstage,NandPdecreasedtoaminimuminliveshrubbiomassandincreasedindeadshrubbiomass.
Fiftyto58yearsafterestablishment,thevegetationcover,productivity,andmortalityofliveshrubsallstabilizedduetotherelativelystablesoilmoistureinthedeepsoillayer(Lietal.
,2004).
ThiscausedNandPdensitiesinbothliveanddeadshrubstoincrease,butvaluesremainedlowerthanthoseatthenativesite.
Oneimportantreasonwasthefactthatvegetationstructurewasdierentatthe58-yearrestoredsite(wherethemainshrubspecieswereA.
ordosica,C.
korshinskii,andH.
scoparium)andthenativesite(dominatedbyA.
ordosica,C.
korshinskii,andC.
lateens).
Fig.
6.
Pdensityof(A)shrubleaves,(B)newbranches,(C)agingbranches,and(D)shrubrootbiomassofliveshrubsinthesand-bindingvegetationsitesandthenativevegetationsite.
Valuesareexpressedasmean±SE.
Lettersindicatesignicantdierencesbetweensites(P<0.
05).
Fig.
7.
Ndensityofabovegroundandroots(A)andPdensityofaboveground,androotbiomass(B)ofdeadshrubs.
Valuesareexpressedasmean±SE.
Lettersindicatesignicantdierencesbetweensites(P<0.
05).
Y.
haotian,etal.
JournalofEnvironmentalManagement245(2019)200–209206Withrestoredvegetationsuccession,moreherbagespeciesinvadedandtherichnessandcoverageofherbaceousspeciesincreased,untilshrub-dominatedvegetationtransitionedtobecomedominatedbyherbs.
Asaresult,NandPdensitiesforherbagelivingbiomass,litter,androotsweresignicantlyhigherattherestoredsitesthanatthesandsite.
Becauseherbagecoveragewashighlycorrelatedwithannualprecipitation(Li,2005),theseplantscompletetheirlifecyclesbeforesummerusingthesoilmoisturefromearlyspringrainfallandwintersnowfall.
Inaddition,someannualgrassesbegintogrowafterrainfallbutdieduringdrought.
Therefore,NandPdensitiesfromrootbiomassatthestudysiteswerefarhigherthanintheabovegroundbiomass.
However,NandPdensitiesforherbagebiomassattherestoredsitesweremuchlowerthanatthenativevegetationsite.
Thiswasprimarilybecausethereweremoreperennialherbagespeciesatthenativesitethanattherestoredsites,suchasStipaglareosaP.
SmirnandArtemisiafrigidaWilld.
Thisresultedinmoreherbagerichness,coverage,andbiomassatthenativesite.
4.
3.
NandPdensitydistributionsindierentcomponentsThereisconstantnutrientcyclingbetweenseveralmajorpools(soil,plantbiomass,andlitter)inthebiosphere.
ThestorageofNandPinanecosystemismediatedbytheinteractionsbetweensoil,plants,andmicrobialprocesses(Fisketal.
,2002).
Hence,quantifyingthesizeanddistributioncharacteristicsofnutrientpoolsforvariouscomponentsisofgreatsignicancetothegeochemicalnutrientcycle.
Ourresultsshowedthattheestablishmentofsand-bidingvegetationsignicantlyaltereddistributionpatternsofNandPpoolsintheplant-litter-soilcontinuumindesertecosystems.
Meanwhile,therelativecontributionsofdierentcomponentstoTNandPdensitieschangedwithvegetationsuccession.
Finally,thedistributionofNandPpoolsatthe58-yearsitewassimilartothenativesite.
Themainreasonforthismaybethatthecompositionanddiversityofherbage,shrub,BSCsandsoilmicro-organisms,shrubbiomass,soiltexture,andsoilmoistureallchangedsignicantlyafterthevegetationestablishedandcontinuedtobeal-teredbyvegetationsuccession(Li,2005).
Becausethechemicalcompositionsofplanttissues,suchaslignin,ber,cellulose,hemi-cellulose,protein,andphenols,aredierentacrossspeciesororgans(Liuetal.
,2016),theymaystronglyinuencethequalityofnutrientinputsandoutputs(Vitouseketal.
,1987).
OurresultsshowedthatNandPinecosystemswereprimarilystoredinsoilsfromnativeandrestoredsites.
STNandSTPdensitiesaccountedfor89.
83%–92.
06%and99.
33%–99.
48%oftheTNandTPdensities,respectively.
Theseresultswerefarhigherthanthosefoundinforestecosystems(ShugaleiandVedrova,2004).
AlthoughSTNandSTPdensitiesvariedwidelyatdierentsites,theirrelativecontributionstoTNandTPdensitiesvariedlittle.
OurresultsindicatedthatherbagebiomassbecameanimportantcomponentofTNandTPaftertheestablishmentofrestoredvegetation,especiallyNandPdensities,whichaccumulatedprimarilyinrootbiomass.
Overtime,NandPdensitiesinherbaceousbiomassincreasedrespectivelyfrom3.
71%to6.
31%,and0.
33%–0.
43%andgraduallyapproachedthevaluesatthenativesite(6.
39%and0.
46%).
Mostgrasseswereannualorbiennial,whichlosetheirabovegroundbiomassandbecomeimportantnutrientinputsafterthegrowingseason.
Inaddition,rootsystemturnoverisanimportantpartofnutrientcycling.
Hence,ourresultsdemonstratedthatherbaceousplantsplayedanin-creasinglyimportantroleintheNandPgeochemicalcyclewiththesuccessionofrestoredvegetation.
OurresultsshowedthatshrubswereanotherimportantNandPpool,inresponsetoappropriatemanagementstrategies.
Meanwhile,thesuccessionofrestoredvegetationsignicantlyaectedtherelativecontributionsofliveanddeadshrubstoTNandTPdensity.
Unlikeherbaceousplants,NandPdensitiesforliveshrubsdecreasedrespec-tivelyfrom4.
55%to1.
07%andfrom0.
33%to0.
13%.
TheNandPdensitiesindeadshrubshadtheoppositetrend.
Ratiosduringthelaterstagesofsuccessionforrestoredvegetationbecamegraduallysimilartothenativesite.
TheresultsimpliedthatshrubsplayedamoreimportantroleintheNandPgeochemicalcycleduringtheearlystagesofrestoredvegetation,whichgraduallydecreasedwithsuccessionuntilitwassi-milartothatofnativevegetation.
Thelignicationofwoodyplantsismuchhigherthanherbaceousplants,andlignininwoodyplantshasFig.
8.
TNandTPdensities,aswellastheaverageannualratesofchangeacrossfoursuccessionalstages.
Valuesareexpressedasmean±SE.
Lettersindicatesignicantdierencesbetweensites(P<0.
05).
Y.
haotian,etal.
JournalofEnvironmentalManagement245(2019)200–209207greaterlongevitythanherbaceousplants(Amthor,2003;Liuetal.
,2016).
Itshouldbenotedthatinthisstudy,NandPdensityinabovegroundbiomasswasmainlystoredinthemechanicalsupportsystems,suchasagingbranches.
Thosecomponentswithhigherligninandbercanbeconservedforalongtimeanddonotdecomposeeasily,especiallyunderdryclimateconditions.
TheseresultsindicatedthatrelativecontributionofshrubstoTNandTPdensitiesatdierentstagesmayprofoundlyaltertheNandPgeochemicalcycleoftheecosystem.
4.
4.
ManagementimplicationsManagementpracticesexertanenormousinuenceonnutrientstatusandperformance,thesizeofvariousnutrientpoolsanduxesbetweenthesepools,andthedistributionofnutrientsinvariouspoolsinmanyterrestrialecosystems(Jcbjretal.
,2006;Liuetal.
,2011).
Ourresultsshowedthatnutrientstatus,pools,andrelativeamountsofTNandTPinsoil,greenherbage,herbageroots,liveshrubs,shrubroots,litter,anddeadshrubsweresignicantlyalteredafterestablishingnewvegetationinashiftingsanddune.
Duetotheconversionoftheshiftingsanddunetorestoredvegetation,therewasasignicantimpactonabioticandbioticfactors,suchassoiltexture,soilwaterdistribution,soiltemperature,microbialcommunities,plantspecies,soilrespiration,andthequantityandqualityoforganicmatterinputsandoutputs(Li,2005;Liuetal.
,2013;Zhangetal.
,2015).
Somestudieshavepredictedthatsuccessionalstatuswithdierentpatternsofbiomassaccumulationandallocationcanregulatethelossandinputoflimitingnutrientsinforestecosystem(Fisketal.
,2002).
OurexperimentsdemonstratedthatallNandPpoolsinrestoredvegetationwerealteredwithsuccessionalstatus.
TheratesofNandPlossoraccumulationvariedbasedontheageoftherestoredecosystem.
Co-limitationofNandPsuggeststhatNandPsimultaneouslylimitproductivityandgrowthinterrestrialandaquaticecosystems(Harpoleetal.
,2011).
Atthesametime,carbon,nitrogen,andphosphoruscyclesareintertwined.
Forthesereasons,NandParetwokeyfactorsrelatedtothegreenhouseeectandglobalclimatechange,soNandPcyclingindierentpoolshascometotheforefrontofecologicalresearch.
Forexample,anincreaseinNinputscanresultinanincreaseincarbondioxide(CO2)uptakeinsometerrestrialecosystems(Thomasetal.
,2010).
Inthisstudy,althoughsoilNandPstoragedecreasedsig-nicantlyintheearlystages(0–50years),soilNandPpoolsincreasedatthelaterstagesforrestoredvegetationandgraduallyapproachedthevaluesfornativevegetation.
WeconcludethatanincreaseinNandPpoolsatthelatestage(50-year)ofsuccessionmayincreasecarbondi-oxideuptakeandstorageinecosystems,whichhasbeenshownbyYangetal.
(2014).
Afterrestoredvegetationwasestablishedfor50years,althoughNandPpoolsintopsoilexceededthatofnativevegetation,thesubsoilhadgreatpotentialforNandPuptakeandstoragecom-paredwiththenativevegetation.
Thereareenormousareasofrestoredvegetationinaridandsemi-aridregions,andnumerousmanagementinterventionshavebeenimplementedbythegovernmentandotherentitiesinrecentyears.
Theestablishmentofrestoredvegetationthroughtheintroductionofxerophyticshrubspeciesinawind-sanddamagedareamayplayavitalroleintheregulationofNandPcyclesandmitigateglobalclimatechange.
5.
ConclusionThedynamicsanddistributionspatternsofNandPpoolsinsoil-plantsystemsweresignicantlyalteredbyvegetationrestorationandsuccession.
NandPwereprimarilystoredinsoils,followedbyherbage,liveshrubs,anddeadshrubs.
TherestoredecosystemwasaNsourceintheearlystageofsuccessionfrom0to50yearsandaNsinkinthelatersuccessionstagefrom50to58years,withstrongpotentialforNandPxation.
VegetationrestorationandsuccessionindesertsmayplayavitalroleintheregulationofNandPcycles.
AcknowledgementsThisresearchwassupportedbytheNationalNaturalScienceFoundationofChinaofChina(GrantNo.
41621001,41530746,41501110,41671111),theStrategicPriorityResearchProgramofChineseAcademyofSciences(GrantNo.
XDA2003010301),andtheWestLightProgramforTalentCultivationofChineseAcademyofSciences.
AppendixA.
SupplementarydataSupplementarydatatothisarticlecanbefoundonlineathttps://doi.
org/10.
1016/j.
jenvman.
2019.
04.
108.
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