土壤学基本知识-土壤有机质性质及其分解

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1、PropertiesofSoilOrganicmatterandItsDecayGeneralpatternofelementcycleinecosystemsPropertiesofSoilOM-1:Chemicalpropertiesoflitterandsoilorganicmatter(OM):Litter(deadleaves,twigsfallingontheground)andsoilorganicmattercontainnutrients&beacriticallinkinnutrientcycles.Decompositionistheprocesst

2、hatconvertstheorganicformsofnutrientstoinorganicformsavailabletoplants.Thenutrientcontentandthechemicalstructureoflitter/OM,determinethequalityoflitter/OM&affectthedecompositionrates.Threegeneralcharacteristicsdeterminethelitter/OMquality:Thetypeofchemicalbonds&energyreleasedastheydecay;T

3、hesizeandspatialcomplexityofthemolecules;Nutrientcontent.1and2determinetheCarbonQualityoflitter/OM,while3determinesNutrientQualityoflitter/OMPropertiesofSoilOM-2:DecompositionofOMtoinorganicmoleculesgothroughalongchainofbiochemicalprocessestograduallydegradecomplexOM,andmanysoilorganismsa

4、ndmicrobesinvolved(recalldetritusfoodweb).Thesesoilorganismsandmicrobesbreak(decay)thechemicalbondsinOMthroughtheenzymestheyproduced(costenergy).ThesoilorganismsandmicrobesdecayOMtorequestenergyandnutrientsforthemselves.Therefore,thehighertheenergy,nutrientcontent,thesimplerthemoleculestr

5、ucturetheOMis,theeasier(faster)itcanbedecomposed.BothOMquality&environmentfactorsaffectthebiochemicalworkofthesoilorganisms/microbes:decompositionisaoxidationprocessrequiringparticipationofsoilorganisms/microbesfactorsaffectsoilorganisms/microbesandgeneralaerationconditionofsoilwillinflu

6、enceratesofdecomposition.PropertiesofSoilOM-3:MajorBiochemicalConstituentsofLitterandTheirDecay:Simplesugars:mono-anddisaccharides:glucose,sucrose..Starch:polymerofnglucoseslinkedby1-4glucosidebond.Cellulose:polymerofnglucoseslinkedby1-4glucosidebond,butslightlydifferent3-Dstructurefromst

7、arch.Hemicellulose:polymerofndifferentsimplesugarstoformchainandbranchedstructures;(nin2≈thousands,nin3&4≈thousandstotensofthousands)PropertiesofSoilOM-4:Hydrocarbons(fatsandwaxes):partiallysaturated,long-chaincarboncompoundsinwhichhydroxyl(OH)groupsaredisplacedbyhy