1
Q
OM connection to C Cycle
A
- few % of OM but very important: nutrients, water capacity, organisms
- Stabilisation of OM: stabilise = long term storage in soil
- Equilibrium of OM: equal input (dead matter) and output (degradation, CO2)
- Sorbent OM: binding of Water, nutrients, pesticides as a filter
- Soil Stabilisation, aggregates: OM as a glue
- OM source of C & energy: serve organisms, plants to degrade
2
Q
Carbon occurrence in soil
A
- reserve carbon: 80% in soil rest in vegetation, soil more efficient for storage
- plants absorbing CO2 from athmosphere, sun as energy source, transform into sugar as energy source and release at root microbiome
- plants capture nutrients from Athmosphere, transport into soil, serves C as an energy source
3
Q
amount of OM in soil
A
Arable soils: humus poor, upper part harvestes so C depleted, 2%
Grassland soils: moderat humus
Forest soils top layer: organic layer, 100% OM
Forest soils mineral soil: humus rich
Wetland soils/Peatland: boggy (sumpfig)
4
Q
concentration vs. stocks of organic C
A
=> Tabelle Folie
- OC = Organic Carbon content
- 2 diff. types of cambsisol, 1 forest 1 cropland
- concentration = content multiplied by area
- low carbon concentration but deep layer so horizon is still bigger
5
Q
global contens & stocks of Organic C
A
- Above & below-ground biomass
- 2/3 of C in OM
- more C below ground except Tropical soils (moisture for microorganisms)
- less C in below ground at Bolear moist
=> Abb. Folie
6
Q
global fluxes and stocks
A
- Athmospheric CO2: 800 in stocks
- Vegetation CO2: 500 in stocks
- Soils CO2: 4000 in stocks
- Fluxes between these + Rivers, highest flux from Athmosphere to Vegetation
- if balance is disrupted: more CO2 in Athmosphere
7
Q
OM Definition
A
- all dead plant/animal substances in/on mineral soil and their organic transformation prodcuts
- Humus
- excl. Edaphon: soil biota with living organisms & roots
8
Q
Mineralization Definition
A
- complete microbial degradation to inorganic substances
- process of degrading fresh OM
9
Q
Humification Definition
A
- formation of humus
- serves as protection of OM from further decomposition
10
Q
Decomposition Definition
A
- breakdown of OM
- transformation of organic residue by hetereotrophic organims leads to differentiation of OM
- plant remains, microbial remains, mineral bound organic substance, charcoal, etc.
- diff. Degradation grades
11
Q
C/N ratio (Carbon/Nitrogen)
A
- indicator for the ease of Decomposition of OM & bio. activity
- smaller ratio by Mineralisation
- the smaller OM the more degradable (mushroom mycelium 15, grass 20, wood 300)
- slow Degradation = higher ratio
- raw humus Layer 30, mineral soil 10
12
Q
Mineralisation Definition
A
- release of CO2 while N is incorporated into microbial biomass
- leads to smaller C/N ratio
13
Q
Composition of OM
A
- plant remains (tissues)
- plant fats & waxes
- cellular constituents
14
Q
Parenchyma tissue (basic)
A
- in living green tissues: leaves, needles, fine roots
- Cellulose & hemicellulose (cell walls)
- proteins
- C/N < 50
15
Q
Lignified tissue
A
- wood part (xylem)
- supporting tissue, solid
- lignified cell wall: cellulose, hemicellulose, lignin
- C/N > 100
16
Q
Cellulose properties
A
- partially crystalline polymer consisting of only Glucose monomers
- > 10000 units form 1 cellulose strand
- rarely appears alone, but with Hemicellulose & Lignin
- also in Protozoa with cell walls
17
Q
Structure of Cellulose
A
- fibrillar structure with crystalline properties (= repetitive)
- formed via hydrogen bonds
- Glucose bound by Hydrogen
18
Q
Hemicellulose properties
A
- in cell walls
- Polymers of diff. sugars, not just Glucose
- more branched, so easier to degrade
- amorphous, not crystaline
19
Q
Cell walls of Plant
A
middle Lamella: Pectin
Primary Cell Wall: Cellulose, Hemicellulose
Plasma Membrane
20
Q
Lignin properties
A
- most common biopolymer in nature after Polysaccharides (hemi/cellulose)
- in cell walls of (vascular) plants
- serves as support Function, linking of individual cells, Protection
21
Q
Lignin structure
A
- aromatic ring of monomer units linked by double C bonds
- complex Polymer, strongly cross-linked
- very hard to degrade
- mostly unbranched Hydrocarbon chain with terminal Carboxyl group
- long chains = hydrophobic, smaller = hydrophilic
- hetereogeneous Substance class: Fatty acids, phospholipids
22
Q
Plants fats/waxes
A
Lipids
Cutin
Suberin
23
Q
Lipids
A
- unbranched Hydrocarbon chains with terminal Carboxyl group
- hetereogeneous substance class: fatty acids, Phospholipids
24
Q
Cutin
A
- macromolecular framework in cuticle (wax layer)
- Hydroxy fatty acids (C16/18)
- serves as Biomarker in soil: degraded roots leaves Suberin
25
Suberin
- cell wall component & outer layer of woody plants
- Bark, roots with particularly high contents
- similar to Cutin, monomers with C20/30
26
Cellular constituents
Proteins
Tannins
Others
27
Proteins
- = Polypeptides, long chains of amino acids/peptides
- Proteins of plant & microbial tissues can be degraded by Microorganisms
- bring energy with N component
- less-stable Plant nutrient
28
Tannins
- Polyphenols that can bind to Protein
- works similar to Lignin
29
Chlorophyll as cellular constituent
- stops forming to save energy
- Plant gets nutrients back
- Carotin instead, leaves get dry and fall down
=> Starch: converted into Glucose if needed
30
Plant residue composition
- diff. Types of fresh litter => OM with diff. compounds
- diff. Degradation rates, shown in CN ratio
- CN changes also with degredation
- Plants taking N from Athmosphere into soil = higher Protein
31
Microbial residue composition
- Substances similar to those in plants (Lig/Sub/Cut plant specific)
- higher Lipids, in Membrane
- higher proportion of componenets with N = smaller C/N ratio
32
Elements in OM that form Minerals
Nitrogen
- almost exclusively binding to OM in soil
- first in microbial biomass then stabilized in OM
- mostly in Peptides
Sulfur
- up to 90% S in organic form, rest in amino acids
Phosphorus
- > 50% bound in form of Orthopohosphate
33
Mineralization & Humification Abb.
- Constituents of organic residue transformed into Products of decomposition
- >50% of Carbohydrates transformed, mostly Mineralization, rest Humification
- can transform into inorganic Products or Humic substances
34
Transformation of organic residue
- 70% transformed into CO2
- 25% into Humus components
- 5% into Biomass
35
Decomposition of the litter
- Litter as primary resource mined by primary decomposers
- Biochemical: splitting of macromolecules, especially Polysaccharides
- Biological: mechan. curshing by gnawing of plant remains by macro & mesofauna, especially Arthropods, woodlice, mites
=> diff. Organisms degrading diff. OM parts
36
degrading by Earthworms
- take leaves, cover them in slime
- pull down into hole, degrade into food
- 20 leaves per night
- excretion is beneficial to Soil & further decomposition
37
Phases of Litter Decomposition
Preliminary phase
Initial phase
Crushing phase
Dismantling & conversion phase
38
Preliminary phase
- biochem. reactions of Substances produced by plant by Hydrolisis & Oxidation
- Degradation of Chlorophyll = autumnal discoloration, saves energy
- starch = transform into Sugar to get energy
- Protein = transform to Amino acids to get taken up
- Cell structure remains intact
39
Initial phase
- Hydrolisis & Oxidation of high polymeric compounds
- Leaching of water-soluble components ( sugar, amino acids)
- strong increase of Microorganisms living from released substances
40
Crushing phase
- Litter partly bitten/eaten/modified by Macrofauna
- excreted again in modified form (earthworms)
- incorporation into Soil by earthworms, arthropods to make accessible for Mesofauna (mites)
41
Dismantling & conversion phase
- enzymatic cleveage of organic fragments
- formation of simple inorganic components (Mineralisation) like CO2, H2O, NH4+
- relat. Enrichment of hardly degradable compounds (tannins)
42
43
Biochemistry of degradation
- easy to hydrolyse Polymers are completely hydrolysed enzymatically in Initial phase
- complex hard to degrade substances first need phys. Degradation before breaking down by Enzyme systems
=> Degradation to low-molecular monomers = microbial food base
44
Biochemistry: easy Polymers
- Proteins: proteases
- Starch: amylases
- Ribonucleic acids: DNAse, RNAse
- simple polar Lipids: lipases, esterases
=> Whatever is easiest to degrade will degrade first
45
Biochemistry: complex Substances
- Cellulose fibrils: Cellulase enzyme complex, detaching of layers
- Lignin: Peroxidase & catalse induced radical reaction
46
Speed of litter degradation
depends on..
- Litter factors
- External & environmental factors
47
Litter factors
- N content of substance (C/N ratio), N increases speed
- Ligning content (ligning/N ratio), higher Ligning the harder to degrade
- Tannin content (polyphenol/N ratio)
48
External & environmental factors
- heat, temperature
- availability of H2O, O2
- pH, neutral best for bacteria, Fungi at acidic
- Inhibitors (bacterides, fungicides)
49
Stabilisation Definition
- = Humification
- general term for processes & mechanisms slowing down Degradation of OM, leading to form Humus
- Accumulation of OM in soil with slowed Degradation
- stabilized OM = older
50
Stabilisation through Recalcitrance
- delayed Degradation due to molecular properties of OM
Primary Recalcitrance
- directly from structural plant cells
- in litter & root existence of C-C bonds of aromatic polymers
Secondary Recalcitrance
- microbial & animal products
- formation of C-C bonds with aromatic polymers & macromolecules
- pyrogenic carbong: highly aromatic , wood burned with little O2 = charcoal
51
Extraction Process of Old Concept
- Soil Product/Sample => Extract with alkali
- if not soluble (at high pH) = Humin
- else treat soluble extract with acid
- if insoluble = Humic Acid, => Redissolve into base & electrolyte => Brown humic Acid that is soluble
- if soluble = Fulvic Acid fraction, => XAD-8 Column Chromatography, => Fulvic Acid
=> formed things thru. Extraction Process
52
Old Concept of Stabilisation
- molecular structure determines timescale of persistence
- Condensation reacts to leaves
- creation of new stable compounds
- Soil => wet chem. extraction => Observation => Interpretation
53
New understanding of Stabilisation
- leaves, stems, roots, fire residues
- inputs of Rhizosphere
- 3 Processes leading to Stabilisation
- age of carbon in deep Soil reveals age & duration of process
- Soil => direct Observation in situ => Interpretation
54
3 Processes of Stabilisation
- Physical disconnection: from degraders & encymes, OM is in aggregate
- Sorption: minerals binding with OM, harder to degrade
- Freezing/Thawing: no bacterial activity
55
Stabilisation: Sorption
- Minerals bound with OM, not easily degraded anymore
56
Stabilisation: phys. Disconnection/Aggregation
- OM in bigger size, disconnected from Degradating factors
- diff. types of Minerals stabilizing it
- spatial location of OM in soil influences accessability for organisms & enzymes
57
Soil Continuum Model
- illustrating Stabilisation thru Aggregation & Sorption
- input of fresh Materials
- Formation & Destruction (Aggregation), Adsorption & Desorption (Sorption) in exchange with the processes
- below 600 Da possible to get taken up by microorganisms
=> the more mineral Surface Adsorption the more stable OM is, the more C can be taken up
58
Molecular diversity Stabilisation
- Monculture not diverse, Microorganism don't need to adapt
- high Energy return, high Decomposition but only 1 Strategy for Degradation
- more microbe diverse OM = more Strategies, need more Energy for those, so slower Decomposing
- more varied OM = more likely to stay stable
59
Spatial hetereogeneity Stabilisation
- Collocation: isolated OM but all in one place
- little Energy needed, but more disperse = harder for Microorganisms to reach & degrade it,
- sequestered between Minerals, spatially separated
60
Temporal variability Stabilisation
- how fast Temp. changes
- little Variability, slow = environment stable, easy Decomposition
- more, faster variation = more diverse for microorganism, more tranpsort of OM
- transported away from aggregate makes it easier to degrade
61
Importance of OM for Soils
- Nutrient source for plants: N, P, S
- exchange properties: binding/absorbing Cations, attaching to Clay minerals, release of nutritious Cations
- promotes Aggregation of clays: stabilizies aggregates, reduces Erosion
- high water binding capacity
- light adsorption: dark OM = warmer
- catalyzes organic pollutant Decomposition
- Carbon storage
62
Clay as carbon estimate
- how much Carbon could Soil contain
- more Clay = more stabilized
63
Carbon storage of OM
- Biochar/Terra preta: makes charcoal, no degrading, poor soil, actively puttin OM onto soil as a solution
- Permafrost carbon
- Peat, moors: too wet, anoxic
64
Humus forms
Mull
Moder
Mor
65
Mull
- most favourable Humus form
- nutrient rich soils
- neutral to slightly acidic
- high microbial activity
- fast Decomposition of litter, incorporating into soil
- no Oa (badly degraded OM)
- found in deciduous forest, species rich grasslands
66
Mor
- unfavourable Humus form
- nutrient poor soils
- acid, wet/dry soils
- low Microbial activity
- mostly fungi
- thick undegraded layer of litter
- little decomposition, no stabilisation
- Oi, Oe, Oa with sharp boundaries
67
Moder
- intermediate between Mull & Mor
- neutral to slightly acidic
- damp
- Oi, Oe, Oa with gradual boundaries
- found in coniferous, deciduous, mixed forests
Soil Science
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