土壤学基本知识-土壤有机质性质及其分解教学教材.ppt
![资源得分’ title=](/images/score_1.gif)
![资源得分’ title=](/images/score_1.gif)
![资源得分’ title=](/images/score_1.gif)
![资源得分’ title=](/images/score_1.gif)
![资源得分’ title=](/images/score_05.gif)
《土壤学基本知识-土壤有机质性质及其分解教学教材.ppt》由会员分享,可在线阅读,更多相关《土壤学基本知识-土壤有机质性质及其分解教学教材.ppt(44页珍藏版)》请在得力文库 - 分享文档赚钱的网站上搜索。
1、土壤学基本知识土壤学基本知识-土壤有土壤有机质性质及其分解机质性质及其分解General pattern of element cycle in ecosystemsProperties of Soil OM-1:Chemical properties of litter and soil organic matter(OM):Litter(dead leaves,twigs falling on the ground)and soil organic matter contain nutrients&be a critical link in nutrient cycles.Decompos
2、ition is the process that converts the organic forms of nutrients to inorganic forms available to plants.The nutrient content and the chemical structure of litter/OM,determine the quality of litter/OM&affect the decomposition rates.Three general characteristics determine the litter/OM quality:1)The
3、type of chemical bonds&energy released as they decay;2)The size and spatial complexity of the molecules;3)Nutrient content.1 and 2 determine the Carbon Quality of litter/OM,while 3 determines Nutrient Quality of litter/OMProperties of Soil OM-2:Decomposition of OM to inorganic molecules go through a
4、 long chain of biochemical processes to gradually degrade complex OM,and many soil organisms and microbes involved(recall detritus food web).These soil organisms and microbes break(decay)the chemical bonds in OM through the enzymes they produced(cost energy).The soil organisms and microbes decay OM
5、to request energy and nutrients for themselves.Therefore,the higher the energy,nutrient content,the simpler the molecule structure the OM is,the easier(faster)it can be decomposed.Both OM quality&environment factors affect the biochemical work of the soil organisms/microbes:decomposition is a oxidat
6、ion process requiring participation of soil organisms/microbes factors affect soil organisms/microbes and general aeration condition of soil will influence rates of decomposition.Properties of Soil OM-3:Major Biochemical Constituents of Litter and Their Decay:1)Simple sugars:mono-and disaccharides:g
7、lucose,sucrose.2)Starch:polymer of n glucoses linked by 1-4 glucoside bond.3)Cellulose:polymer of n glucoses linked by 1-4 glucoside bond,but slightly different 3-D structure from starch.4)Hemicellulose:polymer of n different simple sugars to form chain and branched structures;(n in 2 thousands,n in
8、 3&4 thousands to tens of thousands)Properties of Soil OM-4:5)Hydrocarbons(fats and waxes):partially saturated,long-chain carbon compounds in which hydroxyl(OH)groups are displaced by hydrogen ions(H+)hydrophobic.Such as cutin that is present in the cuticle,the outer waxy layer in plant leaves.Due t
9、o their sizes,and water repellent feature,they are more decay resistant than carbohydratesProperties of Soil OM-5:Major Biochemical Constituents of Litter and Their Decay:6)Polyphenols:made from diff.phenolic acids(tannins);7)Lignin:large,amorphous,very complex compounds,and makes wood woody.From si
10、mple sugars to lignin,the structures of compounds are more complex more energy required to break them;the less energy can be extracted from decaying them,the slower the decay rates are.Properties of Soil OM-6:Due to complexity of lignin in chemistry,its determination is rather proximate:8)Suberin:mo
11、lecules composed hydrocarbons and phenolics low in energy and hydrophobic9)Proteins:macromolecular compound consists of various amino acids not only high carbon quality,but also high nutrient quality due to high N contents.Properties of Soil OM-6:Different plant tissues have different composition of
12、 these carbon compounds different decomposition rats.In litter decay,simple and soluble compounds decay fast,while complex,large compound accumulate(Fahey et al.1984).Properties of Soil OM-7:Litter decay cross certain threshold and become soil organic matter,also called humus,another complex and amo
13、rphous form of OM in ecosystems.What is humus?It is a series of high molecular weight polymers with a high content of phenolic rings and quite variable side chains.It is high in N and large polyphenolic molecules,low in cellulose and hemicellulose.A large%of N is in neither protein no amino acid for
14、m,but presented as chitin(common in the exoskeleton of bugs and fungal hyphae),&heterocyclic compounds(i.e.,phenolic combined with amino groups).Properties of Soil OM-8:Two larger groups of compounds can be separated from humus:fulvic acids and humic acids-organic colloids.Properties of Soil OM-9:Fo
15、rmation of Humus:still not completely comprehended yet.Three hypotheses:Hypothesis I:formed through a slow,but continue modification of existing plant residues,particularly lignin,by microbes condensation into larger&larger molecules with proteins.Hypothesis II:microbes break all large molecules int
16、o smaller ones that then repolymerize chemically&form high molecular humic and fulvic acids.Hypothesis III:intermediate between I and II.Phenolic substances from either lignin or synthesis are converted to quinones and then polymerized.Properties of Soil OM-10:Decomposition and Stabilization of Humu
17、s:Humus decay very slowly because:1)low biochemical quality carbon compounds(lignin and lignin-like compounds);2)humus molecules and clay particles can be bound together by metal cations(chelation),water,sugars and others disrupting spatialalignment of enzymes&humus molecules,deactivate enzymes.Prop
18、erties of Soil OM-11:Minerals,water and OM have very different gravities(minerals 2.2,water 1.0 and OM 1.0.Soils combines mineral and OM with various composition.Therefore,by the gravity,soils are grouped into Heavy and Light fractions.Heavy soil fractions have more minerals and higher bulk densityL
19、ight soil fractions have more OM and low bulk densityIn general,heavy fractions have OM of more decomposed organic fragments,while light fractions,more still-recognizable litter,therefore,they have very different C/N ratios and N release rates.Decomposition of Litter and Soil OM-1:Decomposition of l
20、itter and soil OM are determined by various internal and external variables:litter quality,soil conditions,andenvironmental conditions.Decomposition rates are often measured as a percentage weight loss per unit time,and this yields:%original remaining=e-ktwhere t=time,k=litter-specific decay rate co
21、nstant assume litter decay rate is constant through time,but it is not true,because1.Water soluble compounds can be lost purely by leaching.2.Water insoluble compounds do not decompose much at same time:substances easier to decay decay first.3.Complex high molecular compounds:lignin,suberin can shie
22、ld cellulose from microbial attack.4.Byproducts of decomposition(humus-mineral complex)are very resistant to decay.Decomposition of Litter and Soil OM-2:5.Therefore,litter composition and chemical,physical properties are changing all the time.The equation is just an approximate:%original remaining=e
23、-ktDecomposition of Litter and Soil OM-3:Rate of weight loss from decomposing litter indicates amount of energy and carbon available for microbes.As the energy and C availability for microbes increase,nutrients may become limiting and microbes may uptake nutrients from soil solution.If nutrient pres
24、ented in litter in excess of microbial requirements,nutrients are released as decomposition proceeds.Decomposition of Litter and Soil OM-4:When nutrient is limiting,and microbes uptake nutrients from soil solution,total nutrient contents in litter will increase immobilizationNet increase of absolute
25、 amount of nutrients in decomposing litter is called net immobilizationAs the energy and C yields from decomposition decline,so does the microbial demand for nutrient.Nutrients released from decay increases,plus those from dead microbes excess nutrients released in mineral forms mineralizationSource
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 土壤学 基本知识 土壤有机质 性质 及其 分解 教学 教材
![提示](https://www.deliwenku.com/images/bang_tan.gif)
限制150内