Capsellabursa‐pastorisL.Medik.(shepherd’spurse)myxospermousseedmucilagemechanicallystabilisesclaysoil
Methods:Seedswerewashedind.H20(1:10[w/v])withshaking,8h.A>ercentrifugaBon(5000rpm,20min),themucilage‐containingsupernatantwasfreeze‐dried.Mucilagewasaddedtosoil(aCa‐montmorillonite(clay)at0,0.5and1%[w/w],atsoilwatercontentsrangingfrom140‐200%[w/w]ofclayweight.Shearstress(τ)wasapplied(0.1‐10000Pa@Temp.=20°C;frequency=0.5Hz;gap=2mm).
Results
WenniDeng1,2,3,*,Dong‐ShengJeng1,PeterToorop4,PaulD.Halle\3,GeoffreyR.Squire3,PietroP.M.Ianne\a3
1DivisionofCivilEngineering,UniversityofDundee,DundeeDD14HN,ScotlandUK2CentreforEnvironmentalChangeandHumanResilience(CECHR),UniversityofDundee3TheJamesHuFonInsHtute,Invergowrie,DundeeDD25DA,ScotlandUK4RoyalBotanicGardens,Kew,WakehurstPlace,Ardingly,WestSussexRH176TN,UK
Email:wenni.deng@[email protected]
Figure3.(a)typicalflowcurveofan‘oscillatorystresssweeptest’.(b)–(f)Plotsofrheologyparameters:lossfactor,shearmodulus,viscosity,yieldstressandflowpointstressversussoilwatercontent(%)(respecKvely),forclaysoilscontainingnomucilage(blackdiamond/solidline),0.5%(bluecross/dashedline)and1%(pinktriangle/do@edline)mucilageat20°C.Allexperimentaldatawerefi@edusinganexponenKalcurve,anderrorsbarsdenotetheSEofthemean.
Acknowledgements:ThisPhDstudentshipisfundedbythe
CECHR.PH,GRSandPPMIaresupportedbytheSco\shGovernment.SpecialthanksareextendedtoPaulDHalle@.
IntroducKon• Capsellabursa‐pastorisL.Medik(shepherd’spurse)seedsare
myxospermous.Thatis,theyexudemucilageuponhydraBon.
• Myxospermyappearstobeofgreatecologicalimportancein
waterlimitedenvironments.
• TheuBlityofthemucilagetoimprovesoilmechanicalproperBes
wasinvesBgated.
• RheologymeasuresassessedthephysicalproperBesofamodel
(clay)soil,beforeanda>ertheaddiBonofextractedseedmucilage.
Conclusions• Soilrheologyparameters(G*,η,τy,τf)decreaseaswatercontentincreases.
• Therateofthisdecreaseisreducedwhenisseedmucilagepresent.
• Thereislessaffectofseedmucilageofsoilshearmodulusandviscosity.
• Thegreatestaffectoftheseedmucilageisseenforyield‐andflow‐stress(soilsBffness).
• Thisinfluenceisgreatestathighsoilwatercontent,evenforonly0.5[w/w]mucilage.
• Atlowwatercontents1%mucilagehasgreaterinfluencethan0.5%mucilage.
• Soilwatercontentandrheology‐measurerelaBonshipsareexplainedbyexponenBalcurvefits.
• Seedmucilageincreasessoilresistancetomechanicalstress,evenatlowconcentraBons
• ThisinsightwillbeexploitedusingmathemaKcalmodelling,tofacilitateanassessmentofthe
ecosystemservicesprovisionsthatmightbemadebymyxospermousseeds.
Figure1.Lightmicrographsofshepherd’spurseseedsvisualizeda^er:(a)rutheniumredstainingandilluminaKonwithwhitelight,showingthelocalisaKonofpecKn;(b)calcofluorandilluminaKonwithUVlight,showingcellulose.Where‘m’denotesthemucilage,and‘s’theseed.NotethatthemucilageisabilayerstructurecomprisingpecKnhadcellulose‐thecelluloseconcentratedattheinnerlayer.Scalebar=500μm.
Thetheoryofrheology• RheologyisthescienceofmaterialdeformaBonandflow.
• Materialsmayrangefromideal‐elasBctoideal‐viscous.
• Theparametersassessedforthisstudyaredefinedbelow.
Parameter Rheologyτ RotaBonalshearstress(Pa),appliedforceγ Shearstrain(1)η Viscosity(Pa∙s),G* Complexshearmodulus(Pa),ameasureofsBffness,G' Storagemodulus(Pa),representelasBcbehaviour,G" Lossmodulus(Pa),representviscousbehaviour,
tanδ Lossfactor(1),whereisthephaseshi>angle,
τyYieldstress(Pa),representacriBcalstressthatcauses
irrecoverabledeformaBon
τf Stressatflowpoint(Pa),wherematerialstarttoflow
Figure2.(a)freezedriedmucilage;(b)Ca‐montmorillonit;(c)RotaKonalrheometer
(c)(a) (b)
1000
10000
100000
140 150 160 170 180 190 200
Shearmod
ulusG*(Pa)
Soilwatercontent(%)
100
1000
10000
140 150 160 170 180 190 200Viscosity
η(P
a∙s)
Soilwatercontent(%)
10
100
1000
140 150 160 170 180 190 200
Yieldstressτy(Pa)
Soilwatercontent(%)
0
0.5
1
1.5
2
1
10
100
1000
10000
100000
0.1 1 10 100 1000
tanδ,‐
G',G'',(P
a)
Shearstress,(Pa)τy τf
G’
G’’
tanδ
Flowpoint
LinearViscoelasBcRange YieldStress
0
0.05
0.1
0.15
0.2
0.25
0.3
140 150 160 170 180 190 200
Lossfactorta
nδ
Watercontent(%)
(b)(a)
(c) (d)
(e) (f)
10
100
1000
140 150 160 170 180 190 200
Flow
Pointstressτf(P
a)
Soilwatercontent(%)
m m
(a) (b)
s s
[email protected]‐3‐642‐14870‐5Penfieldetal.2001.PlantCell13:2777‐2791.Puocietal.2008.Amer.J.Agri.Biol.Sci.3:299‐314,200VanOudtshoorn,VanRooyen1999.Dispersalbiologyofdesertplants.Springer.ISBN978‐3‐642‐08439‐3
