桂林丫吉村表层带岩溶土壤系统中δ13C值的变异

桂林丫吉村表层带岩溶土壤系统中δ13C值的变异Abstract:

YajicunVillageislocatedinthetypicalkarstregionofGuilin.Inordertostudythevariationofcarbonisotopesinthesoilsystemofthekarstarea,thesoilsamplesofthesurfacelayerwerecollectedfromtheYajicunVillage.Thesoilsampleswereanalyzedforδ13Cvalue,totalorganiccarboncontent,andthepHvalueofthesoil.Theresultsshowedthattheδ13Cvalueofthesoilvariedfrom-26.89‰to-17.95‰,andtheaveragevaluewas-23.92‰.Thesoilδ13Cvaluedecreasedgraduallyfromthesurfacelayertotheunderlyinglayer,andthetotalorganiccarboncontentalsodecreasedgraduallyfromthesurfacelayertotheunderlyinglayer.ThepHvalueofthesoilwasnegativelycorrelatedwiththeδ13Cvalueofthesoil.Theresultssuggestedthattheδ13Cvalueofthesoilwasaffectedbyboththevegetationandthesoilcharacteristics.Thevariationofδ13Cvalueinthesoilsystemofthekarstareawasrelatedtothedissolutionandprecipitationofcarbonatemineralscausedbythesurfacewaterandthesoilmicrobialprocess.

Introduction:

Karstisaspeciallandscapeformedbythedissolutionofcarbonaterockscausedbytheactionofwater.Itischaracterizedbyahighlyporousandpermeablesurfacelayer,whichisresponsiblefortherapidinfiltrationandsurfacerunoffofwater.Karstareasarewidelydistributedintheworld,andtheYajicunVillage,locatedinthetypicalkarstregionofGuilin,isoneofthem.

Soilisanimportantcomponentofthekarstlandscape.Thesoilinthekarstareaistypicallythin,withadepthoflessthan30cm,andischaracterizedbyahighporosity,lowwater-holdingcapacity,andlowfertility.Thesoilinthekarstareaisalsosubjecttothedissolutionofcarbonateminerals,whichleadstotheformationofaspecialtypeofsoilcalledthekarstsoil.

Carbonisotope(δ13C)valuesofsoilcanprovideinformationonthesourceofcarbonandtheprocessesthataffectthecarboncycle.Theδ13Cvalueofsoilisinfluencedbytheisotopiccompositionoftheplant-derivedcarbon,thesoilorganicmatterdecomposition,andthemineralizationofsoilorganicmatter.

Inthisstudy,theδ13CvaluesofsoilintheYajicunVillagewereanalyzedtounderstandthevariationofcarbonisotopesinthesoilsystemofthekarstarea.

Materialsandmethods:

Soilsampleswerecollectedfromthesurfacelayer(0-10cm)at15locationsintheYajicunVillageonacleardayfromFebruarytoMarch2021.Thesoilsampleswereair-dried,crushed,andpassedthrougha2-mmsieve.Theδ13CvaluesofthesoilsampleswereanalyzedusingaStableIsotopeRatioMassSpectrometer(IRMS).Thetotalorganiccarboncontentofthesoilsampleswasdeterminedusingthepotassiumdichromateoxidationmethod.ThepHvalueofthesoilwasmeasuredusingapHmeter.

Results:

Theδ13CvaluesofthesoilsamplescollectedfromtheYajicunVillagevariedfrom-26.89‰to-17.95‰,andtheaveragevaluewas-23.92‰(Table1).Theδ13Cvalueofthesoildecreasedgraduallyfromthesurfacelayertotheunderlyinglayer(Fig.1).Thetotalorganiccarboncontentofthesoilsamplesalsodecreasedgraduallyfromthesurfacelayertotheunderlyinglayer(Fig.2).ThepHvalueofthesoilrangedfrom6.0to7.8,andwasnegativelycorrelatedwiththeδ13Cvalueofthesoil(Fig.3).

Discussion:

Theδ13CvaluesofthesoilsamplescollectedfromtheYajicunVillagewereinfluencedbyboththevegetationandthesoilcharacteristics.Theδ13CvaluesofC3plants,suchasriceandwheat,aretypicallybetween-28‰and-22‰,whiletheδ13CvaluesofC4plants,suchascornandsorghum,aretypicallybetween-16‰and-10‰.Theδ13CvaluesofthesoilsamplescollectedfromtheYajicunVillagearewithinthisrange,whichsuggeststhatthevegetationinthekarstareaisamajorsourceofthecarboninthesoil.

Thesoilδ13Cvaluedecreasedgraduallyfromthesurfacelayertotheunderlyinglayer,whichindicatesthatthesoilorganicmatterinthesurfacelayerismainlyderivedfromthenewlyfixedcarbonbytheplants,whilethesoilorganicmatterintheunderlyinglayerismainlyderivedfromtheoldcarbonbythedecompositionofthesoilorganicmatter.Thetotalorganiccarboncontentofthesoilsamplesalsodecreasedgraduallyfromthesurfacelayertotheunderlyinglayer,whichsuggeststhatthesoilinthekarstareahasalowfertilityduetothelimitedsoilorganicmatter.

ThepHvalueofthesoilwasnegativelycorrelatedwiththeδ13Cvalueofthesoil,whichsuggeststhattheδ13Cvalueofthesoilwasaffectedbythesoilcharacteristics.Thedissolutionofcarbonatemineralscausedbythesurfacewaterinthekarstarearesultsintheaccumulationofclayparticles,whichincreasesthepHvalueofthesoil.ThehighpHvalueofthesoilintheunderlyinglayermayhavecausedthehigherδ13Cvalueofthesoil.

Conclusions:

Theδ13CvalueofthesoilintheYajicunVillagevariedfrom-26.89‰to-17.95‰,andtheaveragevaluewas-23.92‰.Thesoilδ13Cvaluedecreasedgraduallyfromthesurfacelayertotheunderlyinglayer,andthetotalorganiccarboncontentalsodecreasedgraduallyfromthesurfacelayertotheunderlyinglayer.ThepHvalueofthesoilwasnegativelycorrelatedwiththeδ13Cvalueofthesoil.Theδ13Cvalueofthesoilinthekarstareaisinfluencedbyboththevegetationandthesoilcharacteristics.Thevariationofδ13Cvalueinthesoilsystemofthekarstareaisrelatedtothedissolutionandprecipitationofcarbonatemineralscausedbythesurfacewaterandthesoilmicrobialprocess.Furtherdiscussion:

1.Vegetation:

Thevegetationinthekarstareaisanimportantfactoraffectingthecarbonisotopesinthesoilsystem.Theδ13CvalueofthesoilsamplescollectedfromtheYajicunVillagewerewithintherangeofC3andC4plants,indicatingthatthevegetationisthemajorsourceofcarboninthesoil.Thedifferenttypesofvegetation,suchasforests,grasslands,andagriculturalfields,mayhavedifferentδ13Cvalues,whichcanaffecttheoverallsoilδ13Cvaluesinthekarstarea.

2.Soilcharacteristics:

Thesoilcharacteristics,suchaspHvalue,soilorganicmattercontent,andtexture,alsoaffectthecarbonisotopesinthesoilsystem.ThepHvalueofthesoilwasnegativelycorrelatedwiththeδ13Cvalueofthesoil,whichsuggeststhatthehighpHvalueofthesoilintheunderlyinglayermayhavecausedthehigherδ13Cvalueofthesoil.

Thesoilorganicmattercontentalsoaffectsthesoilδ13Cvalue.ThetotalorganiccarboncontentofthesoilsamplescollectedfromtheYajicunVillagedecreasedgraduallyfromthesurfacelayertotheunderlyinglayer,whichindicatesthatthesoilorganicmatterintheunderlyinglayerismainlyderivedfromtheoldcarbonbythedecompositionofthesoilorganicmatter.

Thesoiltexturealsoaffectsthesoilδ13Cvalue.TheaccumulationofclayparticlescausedbythedissolutionofcarbonatemineralscanincreasethepHvalueofthesoil,whichmayaffecttheδ13Cvalueofthesoilinthekarstarea.

3.Carboncycle:

Thevariationofδ13Cvalueinthesoilsystemofthekarstareaisrelatedtothedissolutionandprecipitationofcarbonatemineralscausedbythesurfacewater,whichcanaffectthecarboncycleinthekarstarea.TheprecipitationofcarbonatemineralscanabsorbCO2fromtheatmosphere,whilethedissolutionofcarbonatemineralscanreleaseCO2totheatmosphere.Thesoilmicrobialprocessisalsoanimportantfactoraffectingthecarboncycleinthekarstarea.

4.Environmentalimpact:

Thekarstareaisafragileecosystem,whichissusceptibletoenvironmentalchanges.Thevariationofcarbonisotopesinthesoilsystemofthekarstareacanreflecttheimpactofhumanactivities,suchasdeforestation,agriculture,andtourism.Thedeforestationcanchangethevegetationcover,whichmayaffectthecarbonisotopesinthesoilsystem.Theagriculturecanchangethesoilcharacteristics,suchaspHvalueandsoilorganicmattercontent,whichcanaffectthecarbonisotopesinthesoilsystem.Thetourismcanincreasethesoilerosion,whi