Table Of ContentScienceoftheTotalEnvironment625(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
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