BE_Chap+2_Basic+features+of+belowground+ecosystem.ppt

Chap2Basicfeaturesofthebelowgroundecosystem,BelowgroundEcology,Whatissoil?,Theunconsolidatedmineralororganicmaterialontheimmediatesurfaceoftheearththatservesasanaturalmediumforthegrowthoflandplants.,SoilIndividuals-PedonsandPolypedons,FromBradyandWeil2002.Fig.3.1,SoilasaNaturalBody,Howissoilformed?,Weathering(accumulationinsitu):Physicaldisintegration(nochangeinchemicalcomposition)Chemicaldecomposition,Soilsareformedbyweatheringofrocksandminerals,Howissoilformed?,Typesofweathering:Physicalweathering:Temperatureormoisturechangestocrackrocksapart(freeze/thaw,wet/dry);Abrasionbywater,ice,andwind(steams,glaciers,waves)Plantroots/animals/humansBiogeochemicalweathering:Water,oxygen,andacidsproducedbyplantrootsandmicrobes/humans,Courtesyof.nzc,Physicalweathering(mostpronouncedincoldanddryclimates),Biogeochemicalweathering(mostcommoninwarmormoistclimates),Factorsinsoilformation,ParentmaterialsClimate(precipitationandtemperature)Topography(slope,aspect,andlandscapeposition)Organisms(nativevegetation,microbes,soilanimals,andhumanbeings)Time,Typesofparentmaterialoutwash(冰水沉积的),lacustrine(湖积的)Physicalcharacteristicsandchemicalcompositionoftheparentmaterialinfluencetheresultingsoil(e.g.Sandstonecoarse-grainedsoil),Parentmaterials,Loess,Weatheringforcesrelatedtoclimate:heat,rain,ice,snow,wind,sunshine,andotherenvironmentalforces,breakdownparentmaterialandinfluencetheratesofsoilformationprocesses,Climate,Topography,Thelocationofasoilonalandscapecanaffecthowtheclimaticprocessesimpactthesoil.Soilsatthebottomofahillarewetterthansoilsontheslopes,andsouth-facingslopesarewarmerthannorth-facingslopes.Vegetationandplantactivitiesalsodifferwithtopography.,Imagecourtesyof,Organisms,Allplantsandanimalsliveinoronthesoil.Theamountofwaterandnutrientsplantstakeupaffectssoilformation.Thewayhumansusesoilsaffectssoilformation.Animalslivinginthesoilaffectdecompositionofwastematerialsandhowsoilmaterialswillbemovedaroundinthesoilprofile.Deadplantsandanimalseventuallybecomeorganicmatterthatenrichesthesoil.,Time,SoilFormation-Summary,Imagecourtesyof.nz,Soilprofilesandhorizons,AllsoilformationfactorsworktogethertocreatecontrastinglayerscalledhorizonsAverticaldisplayofsoilhorizonsiscalledasoilprofile,SoilProfileDescription,Themasterhorizonsandlayers,Imagecourtesyof.nz,Soilhorizonsdefined,OHorizons(Organic)(有机层或覆盖层).TheOgroupiscomprisedoforganichorizonsthatformabovethemineralsoil.Theyresultfromlitterderivedfromdeadplantsandanimals.Ohorizonsusuallyoccurinforestedareasandaregenerallyabsentingrasslandregions.Thespecifichorizonsare:,Oi(L):Organichorizonoftheoriginalplantandanimalresidues,onlyslightlydecomposed(未分解的枯枝落叶层).Also:Litterlayer,orforestfloorinaforestOe(F):Organichorizon,residuesintermediatelydecomposed(半分解的枯枝落叶层).Oa(H):Organichorizon,residueshighlydecomposed(腐殖层).,FromLindahletal2007NewPhytol.Fig.2,Soilhorizonsdefined,Ahorizons.Ahorizonsarethetopmostmineralhorizons.Theycontainastrongmixtureofpartiallydecomposed(humified)organicmatter,whichtendstoshowadarkercolorthanthatofthelowerhorizons.Ehorizons.Ehorizonsarethoseofmaximumleachingoreluviation(灰化过程)ofclay,iron,andaluminumoxides,whichleavesaconcentrationofresistantminerals,suchasquartz,inthesandandsiltsizes.AnEhorizonisgenerallylighterincolorthanA.,AEE/BBtBCC,SoilHorizonsDefined,BHorizons.ThesubsurfaceBhorizonsincludelayersinwhichilluviationofmaterialshastakenplacefromaboveandevenfrombelow.Inhumidregions,theBhorizonsarethelayersofmaximumaccumulationofmaterialssuchasironandaluminumoxidesandsilicateclays.Inaridandsemiaridregions,calciumcarbonate,calciumsulfate,andothersaltsmayaccumulateintheBhorizons.,Bt,Eluviationandilluviation,FigEluviationandilluviationunderhumid,semiaridandaridconditions.(afterMarsh,1987),Soilhorizonsdefined,CHorizons(母质层).TheChorizonistheunconsolidatedmaterialunderlyingthesolum(土体层，A,E,andB,themostweatheredpartofthesoilprofile).Itmayormaynotbethesameastheparentmaterialfromwhichthesolumformed.TheChorizonisoutsidethezonesofmajorbiologicalactivitiesandisgenerallylittleaffectedbytheprocessesthatformedthehorizonsaboveit.Itsupperlayersmayintimebecomeapartofthesolumasweatheringanderosioncontinue.,Soilhorizonsdefined,RLayers(母岩层).Underlyingconsolidatedrock,withlittleevidenceofweathering.TransitionalHorizons.Thesehorizonsaretransitionalbetweenthemasterhorizons(O,A,E,B,C).Theymaybedominatedbypropertiesofonehorizonbuthaveprominentcharacteristicsofanother.Bothcapitallettersareusedtodesignatethetransitionhorizons(e.g.,AE,EB,BE,andBC),thedominanthorizonbeinglistedbeforethesubordinateone.Also:A/E,E/B,etc.,Soilhorizonsdefined,SubordinateDistinctions.Masterhorizonsartefurthercharacterizedbyspecificpropertiessuchasdistinctivecolorortheaccumulationofmaterialssuchasclaysandsalts.Thesesubordinatedistinctionsareidentifiedbyusinglowercaselettersthatdesignatespecificcharacteristics.Examplesare:a:organicmatter,highlydecomposedi:organicmatter,slightlydecomposedk:accumulationofcarbonatesp:plowingorotherdisturbancet:accumulationofsilicateclaysw:distinctivecolororstructure,RequiredReadings:BradyandWeil2002.Chap4:Pages121,123-139,147-151,Soilphysicalproperties,Whatarethecomponentsofasoil?,MineralsintheformofparticlesSoilorganicmatterSoilwaterorsoilsolutionSoilair,Soil:Majorcomponents,Soilphysicalproperties,SoilTexture:affectssoilmoisture,aeration,nutritionSoilStructure:affectssoilmoisture,aggregation,porosity,etc.SoilBulkDensity:dryweightofagivenvolumeofsoilSoilPorosity:airorwaterfilledportionofthesoilmatrixSoilStrength,SoilAeration,SoilTemperature,SoilWater,Soiltexture:Sand+Silt+ClayA.Sand(砂粒),silt(粉砂粒),andclay(黏粒)Sizes(大小分级)andSpecificSurfaceArea(特定表面积)Sand:0.05-2mmSilt:0.002-0.05mmClay:2mm)vs.FineEarth(0.05mm,micropores=0.05mmHeightofcapillaryrise=0.15/radiusArea=r2,sodoublingtheporesizewillquadruplewaterflowatthesamevelocity,SoilPorosity(cont.),FactorsinfluencingPorositySoiltextureSoilorganicmatterSoilfloraandfaunaTraffic,tillageMeasurementSoilcoresofknownvolumeTensiontable(usetensiontodrainthemacropores),SoilPorosity(cont.),A.SoilstrengthaffectsRootgrowthTrafficabilitySoilstrengthisaffectedby:SoilmoistureSoiltextureSoildisturbances(compactionvspuddling)SoilorganicmatterSoilfaunaandfloraC.MeasurementPenetrationresistancewithaconepenetrometer(硬度测定计)Shearresistancewithashearvane(剪度板)Bulkdensity,Soilstrength,Soilsystemisfilledwithlifeandhighlydynamic,Fig1.Activesites,mineralparticlesandwaterfilms,Diversityoforganismsinthesoil,Mycorrhizae(共生真菌),Microbes,Roots,RootsabsorbthewaterandnutrientsthatareneededbytheplantsforphotosynthesisandrespirationRootsinthesoilplayanimportantroleintheactivityoforganisms.Rootsareoftenalittleleaky,andthematerialthattheyleakisreferredtoasrootexudates.,Rhizosphere(根际),Theareaimmediatelyaroundtherootisknownastherhizosphere.TherhizosphereenvironmenthasalowerpH,lowerO2andhigherCO2concentrations.Therhizosphereishigherinsoilorganismactivityduetoincreasedfoodsupplyleakedbytheroot:aminoacids,organicacids,carbohydrates,nucleicacids,growthfactors,enzymes,andsoughed-offtissue.BenefitsfortheplantofhavingarhizosphereincludeenhancedNmineralization,enhancedN2fixation,andnutrientsolubilization.Therhizosphereisdefinedasanintensezoneofstimulatedmicrobialactivityaroundtheroot.Withintherhizospheremicrobialnumbersaremuchgreaterthaninthebulksoil.,Nematodes,NematodesaremicroscopicwormsthatfeedonorganicmatterandothersoilanimalsorinfectplantrootsUndera10 xhandlens,nematodesappearastransparent,thread-likewormsParasiticnematodesarethemostimportantfromanagriculturalstandpoint.Manyplantsareaffected,suchastomatoes,carrots,potatoes,peas,alfalfa,turfgrass,andfruittrees.Nematodescanparasitizevirtuallyallcropsandornamentalplantsandcancausesignificanteconomicdamagebyreducingbothyieldandquality,Fungisaprophyticormycorrhizal,Themaindecomposersoforganicmaterialsinaforestedsoil.Thisismainlybecausetheyaretolerantofacidsoilconditionsandproducesenzymesthatbreakdownlignin.Theirsizevariesfromsingle-cellyeaststomoldsandmushrooms.Mycorrhizaearefungiassociatedwiththefinerootsofmostplants.Thetermitselfmeans“fungusroot”.Therearehundredsspeciesoffungiwhichfunctionasmycorrhiza,Mycorrhizae,Mycorrhizaeareespeciallyimportantinfacilitatinguptakeofphosphorous.Thisenhancementofnutrientuptakeisaresultoftheextensivesystemofhyphaeandmycelia(thread-likefilamentsofthemycorrhizalfungus)thatpervadesoils.Theyfunctionlikeroothairsbutaremuchmorefarreaching,Soilorganicmatter,Allorganicsubstances,bydefinition,containcarbonTheelementcarbonisthefoundationofalllifeSOMistheenergysourceofbelowgroundfoodweb,Whenalltheorganismsaredead,theybecomesoilorganicmatter,Howmuchdorootsdieeveryyearrootturnover?Howmuchdomycorrhizalfungidieeveryyearmycorrhizalturnover?Whatarethequantityandqualityofcarbonandnutrientflowfromplantstosoilanimals?,Soilorganicmatter,SOMconsistsoflivingordeadplantmaterial,livingorganisms,microbialandfaunalproducts,andstabilizedcomplexorganicmattercalledhumusOrganicmatterhasaprofoundimpactonsoilphysical,chemicalandbiologicalproperties,Soilorganicmatter,Organicmatterencompassesallorganiccomponentsofasoil:LivingorganismsFreshresiduesDecomposingorganicmatterStableorganicmatter,Figure.Pathways,pools,andfluxesintheglobalcarboncycle.Notethattheactualnumbersvaryslightlywithdifferentestimates,andareusedhereonlyasguidestothelevelsoffluxesandpools.,Freshresidues,Upto15%oforganicmatterisfreshresidueComprisedmainlyoflitterfall+deadrootsMuchcanberecognizedasplantresidue,Decomposingorganicmatter,PlantmaterialistransformedfromoneorganiccompoundtoanothermainlybyorganismsinthesoilOrganismscreateby-products,wastes,andcelltissueCompoundsreleasedaswastebyoneorganismscanoftenbeusedasfoodbyanother,Credit:UofAExtension&P,Soilorganismsasdecomposers,Acubicmeterofhealthysoilcontainsbillionsofbacteriaandfungi,millionsofnematodes,tensofthousandsofspringtailsandmitesandseveralhundredearthwormsThesecrittersarenaturesrecyclers,convertingplantresidueandanimalmanuresintousablenutrientsandsoilorganicmatter.,Soilorganismsasdecomposers,Thesoilmicroflora(bacteria,fungiandalgae)areresponsiblefor90%ofthedecompositionoforganicmaterial.Plantresidueisthemainfuelforsustainingthebroadspectrumoforganismsresidinginthesoil.,Thedynamicsofsoilmicrobes,Themicrobialpopulationcanincreaserapidlytotakeadvantageofafavorablechangeinthesoilenvironment,doublinginafewhours.Thesizeofthemicrobialpopulationisusuallycontrolledbysoilmoisture,aeration,temperatureandtheirdistributioninthesoil.,Unfortunately,welackabasicunderstandingofmicrobesasdecomposersWhatweknowmostishowlitteractuallydecomposes,Microbialbiomass,AroundrootsInlitterOnhumusOnthesurfaceofsoilaggregatesInspacesbetweensoilaggregates,Highest:,Figure1.Thebiogeochemicalcyclingofcarboninterrestrialecosystems.Thebiogeochemicalcyclingofcarbonistypicallyconceivedofasabox(ecosystempools)andarrow(processescontrollingflowamongpools)diagram.Usingthisapproach,decomposermicroorganisms(highlightedinyellow)havebeenconceptualizedasahomogenouscommunitycatalyzingplant-litterdecay,soilorganicmatterformationandthereturnofCO2totheatmosphereviamicrobialrespiration.Hiddenwithinthisbox-and-arrowconceptualizationarediversebacteriaandfungiwhosephysiologicalattributesgiverisetopopulationandcommunitydynamics,ultimatelyyieldingagloballyimportantbiogeochemicalprocess.,Zaketal2006,Activefraction,Activefraction(10to30%ofthesoilorganicmatter)isresponsibleformaintainingsoilmicroorganisms.Theactivefractionoforganicmatterismostsusceptibletosoilmanagementpractices.(Inactive=humus),Wheatresiduecomposition(g/kg),Solublecomponents288Cellulose361Hemicellulose184Lignin141N-compounds(proteins)9Ash84,Credit:BroderandWagner,1988,Decompositionrates,SolubleComponentsRapidCrudeProteinsHemicelluloseCelluloseFats,WaxesLignin,phenoliccompoundsSlow,Zaketal.2006,Controlsondecompositionrates,BiochemicalcompositionChemicalstructureAmountpresentMicrobialandfaunalactivity,Processes,EnzymaticsolubilizationofsubstratesthroughmicrobialactivityTransformationoforganiccompoundsBiophysicalstabilization(reactionoforganiccompoundswithmineralmaterials)Formationoforgano-claycomplexes,DecompositionSequence,Credit:UofAExtension&P,Stableorganicmatter,SoilorganiccompoundsbecomestabilizedandresistanttofurtherchangesbymicroorganismsBoundinsidesoilaggregatesStabilizedorganicmatteractslikeaspongeandcanabsorbsixtimesitsweightinwater,Humus,Newly-formedhumus-a)combinationofresistantmaterialsfromtheoriginalplanttissue,b)compoundssynthesizedaspartofthemicroorganismstissuewhichremainastheorganismsdie.(FluvicandHumicAcid)HumusisresistanttofurthermicrobialattackNandPareprotectedfromreadysolubility(Scientistsareincreasinglychallengingthis!DetailsinlaterlecturesonsoilCcycling).,Fig.6.12.Structureofamodelhumicacid(Schulten&Schnitzer,1997),Soilfoodweb,Figure1.Thebiogeochemicalcyclingofcarboninterrestrialecosystems.Thebiogeochemicalcyclingofcarbonistypicallyconceivedofasabox(ecosystempools)andarrow(processescontrollingflowamongpools)diagram.Usingthisapproach,decomposermicroorganisms(highlightedinyellow)havebeenconceptualizedasahomogenouscommunityc