Phytoliths and phytolith carbon occlusion in aboveground vegetation of sandy grasslands in eastern Inner Mongolia, China

2018·1.5 MB·English

by  Ning Ru

ScienceoftheTotalEnvironment625(2018)1283–1289
ContentslistsavailableatScienceDirect
Science of the Total Environment
journal homepage: www.elsevier.com/locate/scitotenv
Phytoliths and phytolith carbon occlusion in aboveground vegetation of
sandy grasslands in eastern Inner Mongolia, China
NingRua,b,1,XiaominYanga,1,ZhaoliangSonga,⁎,HongyanLiuc,QianHaoa,XuLiuc,XiuchenWud
aInstituteoftheSurface-EarthSystemScienceResearch,TianjinUniversity,Tianjin300072,China
bSchoolofEnvironmentalandResourceSciences,ZhejiangAgricultureandForestryUniversity,Lin′an,Zhejiang311300,China
cCollegeofUrbanandEnvironmentalSciences,PekingUniversity,Peking100871,China
dCollegeofResourcesScienceandTechnology,BeijingNormalUniversity,Beijing100085,China
H I G H L I G H T S G R A P H I C A L A B S T R A C T
• Grasslands play a crucial role in the
long-term carbon sequestration of
phytoliths.
• Desertificationhasoccurredextensively
insandygrasslandsofnorthernChina.
• Phytolith production flux in sandy
grasslands was 8.94–47.8kgha−1
year−1.
• PhytOCproductionfluxinsandygrass-
landswas0.06–0.48kgha−1year−1.
• Desertificationsignificantlydecreases
thephytolithandPhytOCproduction
fluxes.
a r t i c l e i n f o a b s t r a c t
Articlehistory: Grasslandsplayacrucialroleinthecoupledbiogeochemicalcyclesofcarbon(C)andsilicon(Si)becausethey
Received10November2017 havealargebiogenicSipool(i.e.phytoliths).Inrecentdecades,desertificationhasoccurredextensivelyin
Receivedinrevisedform3January2018 sandygrasslandsduetohumanactivitiesandtoincreasedaridityasaconsequenceofclimatechange.Thepres-
Accepted7January2018
entstudydeterminedthecontentsofphytolithsandCocclusionwithinphytoliths(PhytOC)insandygrassland
Availableonline12January2018
withdifferentvegetationcoveragefromeasternInnerMongolia,Chinaandpreliminarilyassessedtheeffectsof
desertificationonphytolithsandPhytOCproduction.OurresultsshowedthatthephytolithandPhytOCcontents
Editor:JayGan
amongdifferentplantspeciesvariedfrom0.68to9.23%and0.03to1.13‰,respectively.However,thecommu-
Keywords: nity-weightedmeansofthephytolithandPhytOCcontentsforthetotalabovegroundvegetationwereonly1.13–
Phytoliths 3.61%and0.09–0.35‰,respectively,andtheirrespectiveproductionfluxesrangedfrom8.94to47.8kgha−1
PhytOC year−1andfrom0.06to0.48kgha−1year−1,respectively.Asdesertificationprogressed,thetotalcontentsof
Long-termcarbonsequestration phytolithsandPhytOCinabovegroundvegetationdidnotchangesignificantly,whereastheproductionfluxes
InnerMongoliasteppe ofphytolithsandPhytOCweremarkedlyreduced.Thisstudyindicatesthatgrasslanddesertificationdecreases
Grasslanddesertification therangeofthetotalcontentsofphytolithandPhytOCbyreducingspeciesrichness,anddecreasestheproduc-
Grasslandrestoration tionfluxesofphytolithsandPhytOCbyreducingabovegroundbiomass.Grasslandrestorationcantheoretically
enhancetheproductionfluxesofphytolithsandPhytOC~five-fold.
©2018ElsevierB.V.Allrightsreserved.
⁎ Correspondingauthorat:InstituteoftheSurface-EarthSystemScienceResearch,TianjinUniversity,No.92WeijinRoadNankaiDistrict,Tianjin300072,China.
E-mailaddress:[email protected](Z.Song).
1 Theauthorscontributeequallytothemanuscript.
https://doi.org/10.1016/j.scitotenv.2018.01.055
0048-9697/©2018ElsevierB.V.Allrightsreserved.
1284 N.Ruetal./ScienceoftheTotalEnvironment625(2018)1283–1289
1.Introduction hasbeenrecentlychallengedduetothelowerCcontentinphytoliths
extractedbyrapidH SO /H O digestion(SantosandAlexandre,2017).
2 4 2 2
GrasslandsaccountforN20%ofglobalterrestrialarea,andtheyplaya Forgrasslandecosystems,whilephytolithsandPhytOChavebeen
crucialroleinlivestockfarmingandglobalcarbon(C)cycles(Bleckeret wellstudied,(Bleckeretal.,2006;Songetal.,2012;Qietal.,2017;
al.,2006;Jiangetal.,2006;Songetal.,2012).Duetoclimatedryingand Panetal.,2017),changesinphytolithandPhytOCcontents,andinthe
humanactivities(e.g.,overgrazing,croplandmisuse,excessiveexploita- productionfluxesoftheseplantcomponentsinsandygrasslands,as
tionoffuel,andunregulatedcollectionofmedicalplants),halfofthe wellastheirrelationstograsslanddesertificationgradients,arenot
world'sgrasslandareahasbeendegraded(ZhaoandZhao,1993;Zhu wellknown,especiallyinthearidandsemi-aridgrasslandareasof
andChen,1994;Jiangetal.,2006).Desertification,oneofthemostse- China.Therefore,theaimsofthisstudyweretodeterminethecontents
veretypesofgrasslanddegradation,ismainlycharacterizedbyaeolian ofphytolithsandPhytOCinsandygrasslandofeasternInnerMongolia;
(wind-driven)soilerosionofsandygrasslandsinaridandsemi-aridre- toassessthephytolithCsequestrationpotentialofsandygrasslands,
gions(Wang,2000;Yangetal.,2005;Jiangetal.,2006).InChina,there andtoexploretheeffectsofdesertificationongrasslandphytolithCse-
areN6.64×106halandssubjectedtodesertificationinarid,semi-arid questration.Thisstudycouldenhanceourknowledgeofchangesin
anddrysub-humidregions,accountingfor~7%oftheterritory(Zhang phytolithCsequestrationresultingfromchangeingrasslands;present
etal.,2016).Suchalarge-scaledesertificationnotonlyseriouslyexacer- somesuggestionsonhowtoincreasephytolithCsequestration;and
batesthedegradationofthealreadypoorenvironmentalquality,but contributetostudiesofthecoupledbiogeochemicalcyclesofCandSi.
alsoincreasestheproblemofpovertyinpartsofnorthChina(Jianget
al.,2006).
Silicon(Si),thesecondmost-abundantelementintheearth'scrust, 2.Materialsandmethods
canprotectplantsfromvariousabioticandbioticstresses,afteruptake
bytheplantrootsintheformofdissolvedmonosilicicacid(Epstein, 2.1.Experimentalsiteandfieldinvestigation
1994;MaandYamaji,2006).Phytolithsarethemaindepositsofsilica
(SiO )inmanyplanttissues,especiallyattheendpointsoftranspiration, ThisstudywasconductedinthewesternpartoftheNortheastChina
2
thoughthemechanismofSiO depositionisstillunclear(Hodsonetal., Transect,XilingolLeague,InnerMongolia,China(Fig.1).Thearealiesat
2
2005;Schalleretal.,2013).Ingeneral,thephytolithcontentranges 42–44°Nand115–118°E,withanelevationof840–1496m.TheNorth-
fromb0.5%inmostdicotyledonsto~3%intypicaldrylandgrasses, eastChinaTransecthasbeenusedtostudytheresponsesofterrestrial
andmayevenreachupto10–15%intheCyperaceaeandinwetland ecosystemstoglobalclimatechange(Zhouetal.,2002).Thewestern
speciesofthePoaceae(Epstein,1994;Parretal.,2010).Duringthefor- areaoftheNortheastChinaTransectismainlycomprisedofmeadow
mationofphytolithsinplanttissues,0.1%–6%organicC,originating anddesertsteppes,dominatedbyatemperatecontinentalclimate.
largelyfromphotosynthesis,canbeincorporated(Parretal.,2010; Themeanannualtemperatureandprecipitationinthisareaare0–3°C
ParrandSullivan,2011;ZuoandLü,2011;Lietal.,2013;Zuoetal., and295mm,respectively.Grasslandswithsandysoilsubstratesareex-
2017),referredtoasCocclusionwithinphytoliths(PhytOC).Since tensivelydistributedthroughoutthisregion.
phytolithsareresistanttodecomposition,hightemperatureandoxida- WecarriedoutfieldinvestigationandsamplinginJulyandAugustof
tion,thePhytOCcanoccupy82%ofthetotalorganicCinsomesoilsthat 2014,whenplantgrowthisatitsmostmaturestage.Accordingtoour
areN1000-yearsold(ParrandSullivan,2005).Thus,PhytOChasbeen fieldinvestigation,thestudyareahassufferedfromdifferentdegrees
consideredtobeoneofthemostpromisingmechanismsofterrestrial ofdesertification.Oneoftheobviousdesertificationfeaturesisthere-
biogeochemicalCsequestrationatacentennial-millennialscale(Parr gional variation of vegetation coverage. However, it is possible for
andSullivan,2005;Zuoetal.,2014;Songetal.,2012,2013;Dasetal., somewherewithoutdesertificationthatthevegetationcoveragemay
2016),althoughthesignificanceofPhytOCforglobalCsequestration besparse.Therefore,wefirstlysystematicallysetup39sitesbasedon
Fig.1.DistributionofmaingrasslandtypesinChina.FilledtrianglesindicatesamplingsitesfromeasternInnerMongolia.ThedatasetisprovidedbyDataCenterforResourcesand
EnvironmentalSciences,ChineseAcademyofSciences(RESDC,http://www.resdc.cn).
N.Ruetal./ScienceoftheTotalEnvironment625(2018)1283–1289 1285
thevariationofvegetationcoverage,inordertoselectsitessuffering Community-weightedmean(CWM)isbroadlyusedtocalculatethe
fromdesertification.Ateachsite,werandomlysetupthreereplicate communityfunctionaltraitsbymanyresearchers(RicottaandMoretti,
1m×1m quadrats. The coverage, abundance, and height of each 2011;Qiuetal.,2016).Toassessthecontentsofameasuredindex
plantspecieswererecordedineachquadrat(TableS1).Aftercompre- (e.g.,SiO ,phytolith,andPhytOCcontents)ineachplotmorecompre-
2
hensivelyanalyzingthevegetationtype,speciescompositionandvege- hensively,wemodifiedthecommunity-weightedmeanasfollows:
tationcoverageofdifferentsites,12sitesofthe39siteswereselectedto
represent the desertification sites (Table 1). In the field study, the P
abovegroundbiomassofeachquadratwasharvestedtoestimatethe CWMX¼ si¼1IVi(cid:2)Xi ð2Þ
abovegroundnetprimaryproductivity(ANPP)(Table1).Meanwhile, IVts
theabove-groundparts(approximately150g)oftherepresentative
speciesineachquadratwereharvestedtoassessthecontentsandpro-
inwhichXisthemeasuredfunctionalindex,CWM_Xisthecommunity-
ductionfluxesofbothphytolithsandPhytOC,usingthemethodofthe
weightedmeancontentofXineachsite,IV istheimportancevalueof
community-weightedmean. i
sampledspeciesiandcanbecalculatedfromformula(1),X isthecon-
i
tentofXinsampledspeciesi,Sisthetotalnumberofsampledspecies,
2.2.Sampleanalysis
andIV isthetotalIVofallsampledspecies.
ts
Ineachplot,theproductionfluxes(PF)ofdifferentmeasuredfunc-
Thesamplesofabovegroundbiomassandoftherepresentativespe-
tionalindicesintheabovegroundvegetationcouldbeestimatedusing
cieswererinsedwithtapwatertoremoveattacheddust,rinsedthree
thefollowingequation(Songetal.,2012,2013):
timeswithultrapurewater,anddriedat65°Cfor48htoaconstant
weight.Thedriedabovegroundbiomasssamplesweredirectlyweighed
andtherepresentativespeciessamplesweredividedintotwoparts: PFX¼ANPP(cid:2)CWMX ð3Þ
onepartwaspowderedtoanalyzetheSicontent,andtheotherpart
wascuttob2mmtoanalyzephytolithcontent.Thepowderedvegeta-
tionsampleswerefusedwithLi-metaborateandthendissolvedindi- inwhichPF_Xistheproductionfluxofthemeasuredfunctionalindex
lute nitric acid (Li et al., 2013). The Si content of the solution was (X),ANPPistheabovegroundnetprimaryproductivityofeachsite
analyzedbythemolybdenumbluecolorimetricmethod,usingultravio- (Table1),andCWM_Xiscalculatedfromformula(2).
let–visiblespectrophotometer(Jietal.,2017).Inordertomorereliably
quantifythetotalcontentofPhytOC,phytolithswereextractedbythe 2.4.Datastatistics
modifiedmicrowavedigestionmethod;purityofthephytolithswas
testedbyWalkley-Blacktypedigestion(WalkleyandBlack,1934;Liet Excel(2010)andSPSS(18.0)wereusedtostatisticallyanalyzethe
al., 2013; Parr and Sullivan, 2014). The extracted phytoliths were data.One-wayanalysisofvariance(ANOVA)andtheleastsignificant
driedat65°Cfor24hincentrifugetubes,cooled,andthenweighed. difference(LSD)testwereappliedtoexaminethedifferencesbetween
Aftertheweighedphytolithsweredissolvedin1molL−1hydrofluoric thedatagroups.FiguresweremadewithOrigin(8.0).
acid(HF)solutionat50°Cfor1htoreleaseCfromthephytoliths,the
PhytOCconcentrationofthesolutionwasmeasuredbythetraditional 3.Results
potassiumdichromatemethod(Lietal.,2013).TheorganicCdatawas
monitoredwithstandardsoilsamplesofGBW07405.Theprecisionis 3.1.Variationinthemeasuredindicesinsampledspecies
betterthan7%.
SiO contentofallsampledspeciesvariedfrom0.94to7.88%,andthe
2
2.3.Datacalculations phytolithcontentrangedfrom0.68to9.23%(TableS2).Calamagrostis
epigeiosgrowinginsite2hadthehighestabilitytooccludeC(2.33%)
Importancevalue(IV)usesplantspeciesheight,cover,andabun- duringthephytolithformation(TableS2).ThelowestPhytOCcontent
dance to weight each species when constructing a comprehensive (0.03‰)wasfoundinSalsolacollinaandPotentillalongifolia,growing
indexofplantcommunities(Liuetal.,2008).Ineachquadrat,theIV insites1and8,respectively(TableS2).Intheabovegroundpartofdif-
ofeachspecieswascalculatedby: ferentspecies,therewasasignificantpositivecorrelation(R2=0.847,
Pb.01)betweenSiO contentandphytolithcontent(Fig.2a).However,
2
IV¼ðRHþRCþRAÞ=3 ð1Þ therewasnosignificantcorrelationbetweenthephytolithcontentand
Ccontentofphytoliths(Fig.2b).Asignificantpositivecorrelation(R2=
inwhichRHreferstotherelativeheight,RCreferstotherelativecover, 0.558,Pb.01)alsoexistedbetweenphytolithcontentandPhytOCcon-
andRAreferstotherelativeabundanceoftheparticularspecies. tentintheabovegroundpartofallsamples(Fig.2c).
Table1
Informationofsamplingsites.
Sitesa Altitude(m) Vegetationcoverage(%) ANPP(tha−1year−1) Representativeplantspecies
1 1496 80 1.33 Psammochloavillosa,Salsolacollina,Artemisiadesertorum,Leymuschinensis
2 1335 75 1.32 Agropyrondesertorum,Calamagrostisepigeios,Scutellariascordifolia,Artemisiafrigida
3 1350 75 1.84 Bromusircutensis,Potentillalongifolia,Leymuschinensis
4 1357 70 1.46 Artemisiadesertorum,Potentillaacaulis
5 1275 65 1.62 Psammochloavillosa,Carpesiumabrotanoides,Cleistogenessquarrosa
6 1360 65 2.08 Agropyrondesertorum,Silenejenisseensis,Calamagrostisepigeios,Bassiadasyphylla
7 1400 60 1.38 Agropyrondesertorum,Calamagrostisepigeios,Bromusircutensis,Thymusmongolicus
8 1350 60 1.04 Agropyrondesertorum,Carpesiumabrotanoides,Potentillalongifolia
9 1345 50 0.66 Agropyrondesertorum,Potentillanivea,Artemisiadesertorum
10 1350 40 0.68 Artemisiadesertorum
11 1354 35 0.63 Potentillalongifolia,Chamaerhodoserecta
12 1238 15 0.50 Psammochloavillosa,Chenopodiumacuminatum,Thymusmongolicus
a Sequenceofthesamplingsitesbasedonvegetationcoverage(hightolow).
1286 N.Ruetal./ScienceoftheTotalEnvironment625(2018)1283–1289
3.2.Communityweightedmeanofmeasuredindexindifferentsites S2).Forexample,thephytolithcontentofArtemisiadesertorumgrowing
insite1,4,9and10is1.23%,0.68%,3.46%and1.88%,respectively(Table
Accordingtocommunity-weightedmeansofdifferentsampledspe- S2).Asthesamplingsitesaresystematicallyselectedbasedonthevar-
cies,thecorrelationsbetweenSiO contentandphytolithcontent,be- iationofvegetationcoverage,theenvironmentalconditionsamong
2
tweenphytolithcontentandCcontentinthephytoliths,andbetween someofthesesitesaredifferent(e.g.,thedesertificationstatusofsite
phytolithcontentandPhytOCcontentintotalabovegroundbiomass 9andsite10ismoreseriousthanthatofsite1andsite2).Inaddition,
ofallsamplingsites(Fig.S1)weresimilartothosecorrelationsineach compared with previous studies, the phytolith content of Leymus
individualplantspecies(Fig.2).ThecontentofSiO ,phytoliths,Cin chinensisgrowinginsite1(1.89%;TableS2)islowerthanthatgrowing
2
phytoliths,andPhytOCinallsitesrangedfrom1.30%to3.65%,from inmeadowsteppes(2.44%;Songetal.,2012)andtemperateforests
1.13%to3.61%,from0.57%to1.55%,andfrom0.093‰to0.349‰,re- (2.53%;Yangetal.,2015).Thesedifferencesareprobablycausedbyen-
spectively (Table 2). The highest contents of SiO and phytoliths vironmentalfactorssuchastheweatheringstageoftheunderlying
2
(1.30%and1.13%,respectively)werefoundinsite2,whilethehighest rocks, latitude, temperature, topography, land-use change, and the
C in phytoliths (1.55%) and the highest PhytOC content (0.349‰) availabilityofwaterandSiindifferentsoiltypes(Henrietetal.,2008;
were found in site 7. The average values for the content of SiO , Parretal.,2010;ParrandSullivan,2011;Zhangetal.,2012;Yanget
2
phytoliths,Cinphytolith,andPhytOCofallspeciesweresignificantly al.,2016;Yingetal.,2016).
positivelycorrelatedwiththeircommunity-weightedmeans(Fig.3). Duringtheformationofphytolithsinsandygrasslands,thepresent
Furthermore,thephytolithproductionfluxinallsitesrangedfrom studyindicatesthat0.37–2.33%Ccouldbeoccluded(TableS2).Al-
8.94to47.8kgha−1year−1,andthePhytOCproductionfluxranged thoughthecontentofCoccludedbyphytolithsisnotcorrelatedwith
from0.062to0.482kgha−1year−1(Table2). thequantityofthephytoliths(Fig.2b),thepercentageofPhytOCona
dryweightbasisinsampledplantsshowsasignificantlypositivecorre-
lationwiththephytolithcontent(Fig.2c).Thisismainlyattributedto
4.Discussion thephenomenonthatplantsproducinglotsofphytolithsaremorelikely
to have more PhytOC in biomass because of the sheer numbers of
4.1. Factors of controlling phytoliths and PhytOC contents in sandy phytolithsinthatbiomass,eveniftheplantsdonotencapsulatenearly
grasslands asmuchPhytOCperphytolith.ThestudyofParretal.(2010)suggested
thatitwasthenatureofsilicadepositionandtheefficiencyofencapsu-
GrasslandrepresentsaparticularlylargeandactivebiogenicSipool latingCbysilicawithinthecellwallsofphytolithsratherthanthequan-
interrestrialecosystems(Bleckeretal.,2006;Songetal.,2012;Haynes, tityofphytolithsthatdeterminedtherelativePhytOCyield(Parretal.,
2017).Theconstructivespeciesofundisturbedgrassland(e.g.,members 2010).However,itonlyfocusedonbamboospecieswhichallproduce
ofthePoaceaeandCyperaceae)cangenerallyaccumulateSitoconcen- largequantitiesofphytoliths.Onthecontrary,presentstudyincluded
trationsof1–3%,thoughsomeaccompanyingspecies(e.g.,members manyplanttaxawithawiderangeofphytolithproduction.Therefore,
of the Fabaceae) are Si excluders (Epstein, 1994; Conley, 2002; ourresultsimplythatthePhytOCcontentofbiomassismorelikelycon-
Schalleretal.,2016;Table2).Manymonocotsareconsideredtoaccu- trolledbyphytolithquantityinsandygrasslands,thoughthemecha-
mulatemoreSithannon-monocotplantspecies(Epstein,1994).How- nisms underlying the encapsulation of C by silica during the plant
ever,ahighSicontentisnotageneralfeatureofmonocots(Hodsonet growthanditsefficiencyarestillunknown.
al.,2005).Forexample,manyindicatorspeciesofdegradedgrassland
(e.g.Artemisiadesertorum)alsoaccumulatealargeamountofSiduring 4.2.AssessingmeasuresofphytolithandPhytOCproductioninsandygrass-
theirgrowth(TableS2).AsphytolithsarethemaindepositsofSiin landecosystems
planttissues,phytolithcontentissignificantlypositivelycorrelated
withSiO content(Fig.2a).Thisfindingissupportedbythestudiesof Thecompositionofcommunitiesplaysacrucialrolewhenassessing
2
Parretal.(2010),Songetal.(2012,2013),Huangetal.(2015)and community functional traits, especially for grassland ecosystems
Yangetal.(2016). (RicottaandMoretti,2011;Qiuetal.,2016).Forestimatingtheproduc-
Insandygrasslands,thephytolithcontentinplantsrangesfrom tionfluxesofphytolithsandPhytOCingrasslandecosystems,theim-
0.68%to9.23%(Table2).Hodsonetal.(2005)andYangetal.(2015) portanceofspeciesweightingisoftenoverlooked(Songetal.,2012;
studiedtheeffectsofphylogeneticvariationsontheSicontentofplants, Qietal.,2017).Aftercommunityweighting,therewasasignificantly
suggestingthatSicontent,andthusphytolithproduction,wasmore positivecorrelationbetweencommunityweightedmeansandtheaver-
likelyinfluencedbythehigher-levelphylogeneticpositionofaplant agevaluesofallmeasuredindicesindifferentsamplingsites,buttheav-
species.Inpresentstudy,thephytolithcontentsofthesomeplantspe- eragevaluesweregenerallyhigherthantheweightedmeans,exceptfor
ciesgrowingindifferentsamplingsitesaremarkedlydifferent(Table thecontentofCinphytoliths(Fig.3).Thus,usingtheaveragevaluesto
Fig.2.Relationship(a)betweenSiO2contentandphytolithcontent,(b)betweenphytolithcontentandCcontentinphytoliths,and(c)betweenphytolithcontentandPhytOCcontentin
differentspecies.
N.Ruetal./ScienceoftheTotalEnvironment625(2018)1283–1289 1287
Table2
ContentsofSiO2,phytoliths,CinphytolithsandPhytOC,andtheproductionfluxesofphytolithandPhytOCindifferentsamplingsites.
Sites SiO2(%) Phytoliths(%) Cinphytoliths(%) PhytOC(‰) Phytolithproductionflux(kgha−1year−1) PhytOCproductionflux(kgha−1year−1)
1 1.60(0.06) 1.25(0.05) 0.79(0.06) 0.093(0.004) 16.6(0.73) 0.123(0.005)
2 3.65(0.07) 3.61(0.14) 1.16(0.05) 0.324(0.022) 47.8(1.91) 0.430(0.029)
3 1.30(0.04) 1.13(0.03) 1.43(0.03) 0.159(0.000) 20.8(0.50) 0.293(0.000)
4 2.38(0.13) 2.44(0.04) 1.09(0.10) 0.170(0.013) 35.6(0.64) 0.249(0.018)
5 1.57(0.04) 1.19(0.01) 1.16(0.13) 0.134(0.016) 19.4(0.08) 0.217(0.025)
6 1.79(0.03) 1.47(0.11) 1.26(0.03) 0.144(0.011) 30.6(2.20) 0.300(0.022)
7 3.24(0.07) 2.35(0.13) 1.55(0.13) 0.349(0.033) 32.5(1.81) 0.482(0.045)
8 1.79(0.02) 1.60(0.13) 0.80(0.08) 0.153(0.008) 16.7(1.35) 0.159(0.009)
9 2.34(0.13) 2.43(0.09) 0.81(0.06) 0.155(0.008) 16.0(0.58) 0.102(0.005)
10 2.24(0.08) 1.88(0.36) 0.86(0.16) 0.156(0.000) 12.8(2.46) 0.106(0.000)
11 2.38(0.04) 2.02(0.06) 0.57(0.03) 0.146(0.007) 12.8(0.37) 0.093(0.004)
12 2.15(0.06) 1.79(0.07) 0.83(0.02) 0.123(0.004) 8.94(0.34) 0.062(0.002)
Datapresentascommunity-weightedmeanswithstandarddeviation(inbrackets).
assessthecontentsofSiO ,phytoliths,andPhytOCinsandygrasslands fieldinvestigation,allofoursamplingsiteshavesufferedfromdifferent
2
mayoverestimatetheresults.Consideringthatthecorrelationsbe- degreesofdesertification.Ingeneral,desertificationcanleadtode-
tweenSiO contentandphytolithcontent,betweenphytolithcontent creasesinplantbiodiversity,abovegroundbiomass,andANPPofthe
2
andCcontentinthephytoliths,andbetweenphytolithcontentand grasslands(Yangetal.,2005).Inthepresentstudy,thesignificantpos-
PhytOCcontentinallsamplingsitesafterweighting(Fig.S1)weresim- itivecorrelationbetweenvegetationcoverageandANPPindifferent
ilartothosecorrelationsineachindividualplantspecies(Fig.2),the sitesimpliesthat,thelowerthevegetationcoverage,themoresevere
presentstudysuggestedthatusingtheweightedmeantoassessthe thedesertification(Fig.4a).Toassesstheeffectsofdesertificationpro-
productionofSiO ,phytoliths,andPhytOCinsandygrasslandswas cessonthedistributionandproductionofphytolithsandPhytOC,all
2
morereliablethanusingthearithmeticmean. thedesertificationsitesarecategorizedintothreegroups,basedon
thevariationrangeofcurrentvegetationcoverage,namely≥70%,70–
4.3.EffectsofdesertificationonphytolithandPhytOCproduction 50%,and≤50%,respectively(Fig.5).Althoughthesethreegroupsdo
notrepresenttheactualdegreeofdesertification,theycanimplythein-
Desertification,oneofthemostseveretypesofgrasslanddegrada- creasingtrendofdesertificationtosomeextent.
tion,mainlyoccursinsandygrasslandsinaridandsemi-aridregions Itisreportedthatthestorageofsoilnutrientsdecreasessignificantly
(Wang,2000;Yangetal.,2005;Jiangetal.,2006).Accordingtoour asgrasslanddesertificationprogresses(Larneyetal.,1998;Duanetal.,
Fig.3.Relationshipbetweenaveragevaluesandcommunityweightedmeansofmeasuredindicesforallsampledspeciesindifferentsamplingsites.(a)SiO2,(b)phytolith,(c)Cin
phytolith,and(d)PhytOC.
1288 N.Ruetal./ScienceoftheTotalEnvironment625(2018)1283–1289
Fig.4.Relationship(a)betweenvegetationcoverageandANPP,(b)betweenANPPandphytolithproductionflux,and(c)betweenANPPandPhytOCproductionfluxindifferentsampling
sites.
2001;Fengetal.,2002;Zhouetal.,2008;KukalandBawa,2014).How- etal.,2015;TableS2).Correspondingly,theexacerbationofdesertifica-
ever,thecontentsofphytolithsandPhytOCinabovegroundvegetation tionwillinfluencethedistributionpatternsofphytolithandPhytOC
exhibitnosignificantvariationamongsitesofdifferentdesertification content(Fig.5a,b).Furthermore,theproductionfluxesofphytoliths
status(Fig.5a,b).Zhouetal.(2008)hasconfirmedthat,aswellasphy- andPhytOCaresignificantlycorrelatedwiththeANPPofaboveground
tolithandPhytOC contents,theconcentration ofCandnitrogenin vegetationinterrestrialecosystems(Bleckeretal.,2006;Songetal.,
plantsandplantlitterdonotsignificantlydecreasewiththedesertifica- 2012;Fig.4b,c),whichresultsinadeclineinboththevariationranges
tionprocess.Thesefindingsindicatethattheeffectsofdesertification andthevaluesofphytolithproductionflux,aswellasPhytOCproduc-
processonthetotalcontentsofphytolithsandPhytOCintheabove- tionflux,asdesertificationproceedsonaregionalscale(Fig.5c,d).
groundbiomassareweak. Generally,aslongasthedesertificationstatushasnotexceededthe
Inourstudyareas,asthestageofdesertificationincreased,thecom- capacity for self-recovery, grasslands generally restore themselves
plexplantcommunitygraduallydegeneratesintosimplecommunity whengrazingisstopped(Liuetal.,2002).Forexample,boththevege-
comprisedmainlyofdrought-resistantsandyspecies(e.g.Artemisia tation coverage and species richness in extremely degraded sandy
desertorum,Psammochloavillosa,Agropyrondesertorum).Thedecrease grasslandincreaseovertimefollowingexclosureandgrazingprohibi-
inplantbiodiversitymeansthatthevariationintherangeofphytolith tioninanattempttoachievenaturalrevegetation(Zhangetal.,2016).
andPhytOCcontentsinabovegroundvegetationdecreasedbecause Inaddition,appropriatenitrogenadditiontodegradedgrasslandsis
thephytolithandPhytOCcontentsvariedamongthedifferentplant alsoaneffectivewaytoenhancetheabovegroundbiomass(Xuetal.,
species(Hodsonetal.,2005;Parretal.,2010;ZuoandLü,2011;Yang 2015)andthephytolithandPhytOCcontentsinherbs(Zhaoetal.,
Fig.5.Boxplotsshowingvariationsin(a)phytolithcontent,(b)PhytOCcontent,(c)phytolithproductionflux,and(d)PhytOCproductionfluxunderdifferentdesertificationstatus.
DifferentlowercaselettersindicatesignificantdifferencesbetweengroupsatPb.05levelbasedontheleastsignificantdifference(LSD)test.Thetop,midandbottomlineofthebox
representtheupperquartiles,medianandlowerquartiles,respectively.Thetopandbottombarrepresentthemaximumandminimum,respectively.
N.Ruetal./ScienceoftheTotalEnvironment625(2018)1283–1289 1289
2016).Therefore,iftheseveredesertificationgrasslandcouldrecoverto Liu,M.,Jiang,G.,Li,Y.,Gao,L.,Yu,S.,Niu,S.,Li,L.,2002.Anexperimentalanddemonstra-
itsinitiallevel,theproductionfluxesofphytolithsandPhytOCwould tEicoonla.lSisntu.2d3y,o2n71r9e–st2o7r2a7ti.onofdegradedecosystemsinHunshandakSandland.Acta
markedlyincreaseatleastfive-fold.Inpresentstudy,onlytheabove- Liu,H.,Yin,Y.,Tian,Y.,Ren,J.,Wang,H.,2008.Climaticandanthropogeniccontrolsoftop-
groundvegetationwasconsidered.Furtherstudiesinsandygrasslands soilfeaturesinthesemi-aridEastAsiansteppe.Geophys.Res.Lett.35,L04401.
arerequiredtoassessmorecomprehensivelytheeffectsofdesertifica- Ma,J.F.,Yamaji,N.,2006.Siliconuptakeandaccumulationinhigherplants.TrendsPlant
Sci.11,392–397.
tiononphytolithCsequestration,aswellasthecoupledcyclesofC Pan,W.,Song,Z.,Liu,H.,VanZwieten,L.,Li,Y.,Yang,X.,Han,Y.,Liu,X.,Zhang,X.,Xu,Z.,
andSi. Wang,H.,2017.Theaccumulationofphytolith-occludedcarboninsoilsofdifferent
grasslands.J.SoilsSediments17,2420–2427.
Parr,J.F.,Sullivan,L.A.,2005.Soilcarbonsequestrationinphytoliths.SoilBiol.Biochem.37,
5.Conclusions 117–124.
Parr,J.F.,Sullivan,L.A.,2011.Phytolithoccludedcarbonandsilicavariabilityinwheatcul-
Insandygrasslands,phytolithandPhytOCcontentsamongdifferent tivars.PlantSoil342,165–171.
Parr,J.F.,Sullivan,L.A.,2014.Comparisonoftwomethodsfortheisolationofphytolithoc-
plantspeciesvariedfrom0.68to9.23%andfrom0.03to1.13‰,respec- cludedcarbonfromplantmaterial.PlantSoil374,45–53.
tively.ThephytolithandPhytOCcontentsofthetotalabovegroundveg- Parr,J.F.,Sullivan,L.A.,Chen,B.,Ye,G.,Zhang,W.,2010.Carbonbio-sequestrationwithin
etation in sandy grasslands were 1.13–3.61% and 0.09–0.35‰, thephytolithsofeconomicbamboospecies.Glob.Chang.Biol.16,2661–2667.
respectively. Production flux of the phytoliths and PhytOC ranged Qi,L.,Li,F.Y.,Huang,Z.,Jiang,P.,Baoyin,T.,Wang,H.,2017.Phytolith-occludedorganic
carbonasamechanismforlong-termcarbonsequestrationinatypicalsteppe:the
from8.94to47.8kgha−1year−1andfrom0.06to0.48kgha−1year− predominantroleofbelowgroundproductivity.Sci.TotalEnviron.577,413–417.
1,respectively.Althoughthegrasslanddesertificationstatusdidnotsig- Qiu,S.,Liu,H.,Zhao,F.,Liu,X.,2016.Inconsistentchangesofbiomassandspeciesrichness
nificantlyaffectthephytolithandPhytOCcontentsofthetotalabove- Ricoattlao,nCg.,aMporreectitpi,itMat.i,o2n01g1ra.dCiWenMtianntdemRapoe'sraqtueasdteraptpice.dJi.vAerrisdityE:naviurnonifi.e1d3f2r,a4m2e–w48o.rkfor
groundvegetation,thedistributionpatternsandproductionfluxesof functionalecology.Oecologia167,181–188.
phytolithsandPhytOCcouldbemarkedlyinfluencedasdesertification Santos,G.M.,Alexandre,A.,2017.Thephytolithcarbonsequestrationconcept:factorfic-
progressed. With the exacerbation of desertification, the variation tion?Acommenton“Occurrence,turnoverandcarbonsequestrationpotentialof
phytolithsinterrestrialecosystemsbySongetal.”.EarthSci.Rev.164,251–255.
rangesandvaluesofphytolithandPhytOCproductionfluxdecreased. Schaller,J.,Brackhage,C.,Paasch,S.,Brunner,E.,B€aucker,E.,Dudel,E.G.,2013.Silicaup-
Restoration of grassland could theoretically improve phytolith and takefromnanoparticlesandsilicacondensationstateindifferenttissuesofPhragmi-
PhytOC production flux~five-fold. As the stability and storage of tesaustralis.Sci.TotalEnviron.442,6–9.
Schaller,J.,Roscher,C.,Hillebrand,H.,Weigelt,A.,Oelmann,Y.,Wilcke,W.,Ebeling,A.,
phytolithsandPhytOCinsandygrasslandsoilsarestillunknown,future Weisser,W.W.,2016.PlantdiversityandfunctionalgroupsaffectSiandCapoolsin
follow-upworkonthistopicshouldincludemeasurementofphytoliths abovegroundbiomassofgrasslandsystems.Oecologia182,277–286.
andPhytOCinthesegrasslandsoils. Song,Z.,Liu,H.,Si,Y.,Yin,Y.,2012.TheproductionofphytolithsinChina'sgrasslands:im-
Supplementarydatatothisarticlecanbefoundonlineathttps://doi. p18li,ca3t6io4n7s–3to65th3e. biogeochemicalsequestrationofatmosphericCO2.Glob.Chang.Biol.
org/10.1016/j.scitotenv.2018.01.055. Song,Z.,Liu,H.,Li,B.,Yang,X.,2013.Theproductionofphytolith-occludedcarbonin
China'sforests:implicationstobiogeochemicalcarbonsequestration.Glob.Chang.
Biol.19,2907–2915.
Acknowledgements
Walkley,A.,Black,I.A.,1934.AnexaminationoftheDegtjareffmethodfordetermining
soilorganicmatter,andaproposedmodificationofthechromicacidtitrationmeth-
WeacknowledgethesupportfromtheNationalNaturalScience od.SoilSci.37,29–38.
Wang,T.,2000.LanduseandsandydesertificationinnorthChina.J.DesertRes.20,
FoundationofChina(41522207,41571130042)andtheState'sKeyPro- 103–108(inChinese).
jectofResearchandDevelopmentPlanofChina(2016YFA0601002). Xu,X.,Liu,H.,Song,Z.,Wang,W.,Hu,G.,Qi,Z.,2015.Responseofabovegroundbiomass
Wedeclarenoconflictofinterest. anddiversitytonitrogenadditionalongadegradationgradientintheInnerMongo-
liansteppe,China.Sci.Rep.5,10284.
Yang,X.,Zhang,K.,Jia,B.,Ci,L.,2005.DesertificationassessmentinChina:anoverview.
References J.AridEnviron.63,517–531.
Yang,X.,Song,Z.,Liu,H.,Bolan,N.S.,Wang,H.,Li,Z.,2015.Plantsiliconcontentinforests
Blecker,S.W.,McCulley,R.L.,Chadwick,O.A.,Kelly,E.F.,2006.Biologiccyclingofsilica ofnorthChinaanditsimplicationsforphytolithcarbonsequestration.Ecol.Res.30,
acrossagrasslandbioclimosequence.Glob.Biogeochem.Cycles20,GB3023. 347–355.
Conley,D.J.,2002.Terrestrialecosystemsandtheglobalbiogeochemicalsilicacycle.Glob. Yang,X.,Song,Z.,Sullivan,L.A.,Wang,H.,Li,Z.,Li,Y.,Zhang,F.,2016.Topographiccontrol
Biogeochem.Cycles16,1121. onphytolithcarbonsequestrationinmosobamboo(Phyllostachyspubescens)ecosys-
Das,S.K.,Avasthe,R.,Singh,M.,2016.Needforphytolith-occludedcarbonresearchin tems.CarbonManage.7,105–112.
India.Curr.Sci.110,2046. Ying,Y.,Lou,K.,Xiang,T.,Jiang,P.,Wu,J.,Lin,W.,Huang,Z.,Chang,S.X.,2016.PhytOC
Duan,Z.,Xiao,H.,Dong,Z.,He,X.,Wang,G.,2001.EstimateoftotalCO2outputfrom stockinforestlitterinsubtropicalforests:effectsofparentmaterialandforesttype.
desertifiedsandylandinChina.Atmos.Environ.35,5915–5921. Ecol.Eng.97,297–303.
Epstein,E.,1994.Theanomalyofsiliconinplantbiology.Proc.Natl.Acad.Sci.91,11–17. Zhang,S.,Zhang,J.,Slik,J.W.,Cao,K.,2012.Leafelementconcentrationsofterrestrial
Feng,Q.,Endo,K.N.,Cheng,G.D.,2002.Soilcarbonindesertifiedlandinrelationtosite plantsacrossChinaareinfluencedbytaxonomyandtheenvironment.Glob.Ecol.
characteristics.Geoderma106,21–43. Biogeogr.21,809–818.
Haynes,R.J.,2017.ThenatureofbiogenicSianditspotentialroleinSisupplyinagricul- Zhang,J.,Gu,P.,Li,L.,Zong,L.,Zhao,J.,2016.Changesofsoilparticlesizefractionalonga
turalsoils.Agric.Ecosyst.Environ.245,100–111. chronosequenceinsandydesertifiedland:afundamentalprocessforecosystemsuc-
Henriet,C.,Bodarwé,L.,Dorel,M.,Draye,X.,Delvaux,B.,2008.Leafsiliconcontentinba- cessionandecologicalrestoration.J.SoilsSediments16,2651–2656.
nana(Musaspp.)revealstheweatheringstageofvolcanicashsoilsinGuadeloupe. Zhao,H.,Zhao,X.,1993.Theecologicalenvironmentdegradationanditscontrolinthe
PlantSoil313,71–82. semi-droughtregionofNorthernChina.AridZoneRes.10,44–48(inChinese).
Hodson,M.J.,White,P.J.,Mead,A.,Broadley,M.J.,2005.Phylogeneticvariationinthesili- Zhao,Y.,Song,Z.,Xu,X.,Liu,H.,Wu,X.,Li,Z.,Guo,F.,Pan,W.,2016.Nitrogenapplication
concompositionofplants.Ann.Bot.96,1027–1046. increasesphytolithcarbonsequestrationindegradedgrasslandsofNorthChina.Ecol.
Huang,Z.,Li,Y.,Chang,S.X.,Jiang,P.,Meng,C.,Wu,J.,Zhang,Y.,2015.Phytolith-occluded Res.31,117–123.
organiccarboninintensivelymanagedLeibamboo(Phyllostachyspraecox)stands Zhou,G.,Wang,Y.,Wang,S.,2002.Responsesofgrasslandecosystemstoprecipitation
andimplicationsforcarbonsequestration.Can.J.For.Res.45,1019–1025. andlandusealongtheNortheastChinaTransect.J.Veg.Sci.13,361–368.
Ji,Z.,Yang,X.,Song,Z.,Liu,H.,Liu,X.,Qiu,S.,Li,J.,Guo,F.,Wu,Y.,Zhang,X.,2017.Silicon Zhou,R.,Li,Y.,Zhao,H.,Drake,S.,2008.DesertificationeffectsonCandNcontentofsandy
distributioninmeadowsteppeandtypicalsteppeofnorthernChinaanditsimplica- soilsundergrasslandinHorqin,northernChina.Geoderma145,370–375.
tionsforphytolithcarbonsequestration.GrassForageSci.00:1–11.https://doi.org/ Zhu,Z.,Chen,G.,1994.SandyDesertificationinChina.SciencePress,Beijing,China(in
10.1111/gfs.12316. Chinese).
Jiang,G.,Han,X.,Wu,J.,2006.RestorationandmanagementoftheInnerMongoliagrass- Zuo,X.,Lü,H.,2011.Carbonsequestrationwithinmilletphytolithsfromdry-farmingof
landrequireasustainablestrategy.Ambio35,269–270. cropsinChina.Chin.Sci.Bull.56,3451–3456.
Kukal,S.S.,Bawa,S.S.,2014.Soilorganiccarbonstockandfractionsinrelationtolanduse Zuo,X.,Lu,H.,Gu,Z.,2014.Distributionofsoilphytolith-occludedcarbonintheChinese
andsoildepthinthedegradedShiwalikshillsoflowerHimalayas.LandDegrad.Dev. LoessPlateauanditsimplicationsforsilica-carboncycles.PlantSoil374,223–232.
25,407–416. Zuo,X.,Lu,H.,Jiang,L.,Zhang,J.,Yang,X.,Huan,X.,He,K.,Wang,C.,Wu,N.,2017.Dating
Larney,F.J.,Bullock,M.S.,Janzen,H.H.,Ellert,B.H.,Olson,E.C.S.,1998.Winderosioneffects riceremainsthroughphytolithcarbon-14studyrevealsdomesticationatthebegin-
onnutrientredistributionandsoilproductivity.J.SoilWaterConserv.53,133–140. ningoftheHolocene.Proc.Natl.Acad.Sci.114,6486–6491.
Li,Z.,Song,Z.,Parr,J.F.,Wang,H.,2013.OccludedCinricephytoliths:implicationstobio-
geochemicalcarbonsequestration.PlantSoil370,615–623.