Questions

Questions
• What is the mechanism of the ocean CO2 sink?
• What is the mechanism of the land CO2 sink?
• What is the mean residence time of carbon in the
– Atmosphere?
– Land?
– Ocean?
• What drives the changes in the C sink strength in
– Oceans?
– Land?
1
Carbon turnover
in terrestrial
ecosystems
Soil: Basics &
soil organic carbon
23.4.2009
2
Carbon turnover in terrestrial ecosystems
• Definitions
• Mean residence time
• GPP – NPP – NEP – NBP
• Measurement of carbon stocks
• Ecosystem C budgets
3
Concept of mean residence time
Mean residence time = concept of how long
molecules remain in a pool –
dependent on reaction kinetics and pool size.
MRT = Pool size / input per year
Pool size depends on decay rate, which is
ideally exponential.
x
Time
Residence time
distribution in a
pulse experiment
4
C balance in managed ecosystems
NBP
NEP
NPP
GPP
Photosynthesis Autotrophic
respiration
Heterotrophic
respiration
Cuts
Manure
5
Terrestrial carbon fluxes
GPP
120 (100%)
Plant
Heterotrophic Disturbance
respiration respiration or harvest
60 (50%)
50 (41.7%)
9 (7.5%)
NPP
60 (50%)
Global C fluxes in Pg yr-1
NEP
10 (8.3%)
NBP
±1 (0.8%)
6
Measuring ecosystem C components and fluxes
C stocks
C fluxes
Biomass inventory
Leaf photosynthesis
Ground vegetation inventory
Dendrometers: Tree growth
Soil C stocks
Litter fall
Root biomass
Soil respiration
Litter turnover (incubations)
7
Soil inventory
Biomass
Tree growth
Litterfall
Ground vegetation
Mineralisation
MRT of soil C
Soil
description
Soil fauna
Soil respiration
8
Litter fall
Biomass
Tree growth
Litterfall
Ground vegetation
Mineralisation
MRT of soil C
Soil
description
Soil fauna
Soil respiration
9
Eddy covariance
Continuous monitoring of
- CO2, H2O concentration change
- vertical windspeed
10
Net C ecosystem-atmosphere exchange
Eddy covariance measurements
Eddy covariance
The technique is based on the
covariance between concentration
of scalars
Continuous monitoring of
- CO2, H2O concentration change
- vertical windspeed
and vertical wind velocity
measurements.
The turbulent flux
of a scalar
can be written as:
Fc = ρ w + ρ ′ w ′
11
Typical annual C budget in deciduous forest
[g C m-2 yr-1]
12
courtesy of W. Kutsch
C flow at ecosystem level
Schulze et al. 2002, Fig. 3.3.1
13
Physical drivers of daily CO2 fluxes
14
NEE = Net Ecosystem Exchange
15
Reco = Ecosystem respiration
16
(Lloyd and Taylor, 1994)
Modellierter CO2-Austausch:
17
Annual GEP, NEE and Reco in a Dutch peatland
18
Net C balance (NEP) in land use systems of Thuringia
19
Courtesy: MPI-BGC
C balance at Hainich national park
Ecosystem carbon storage (g C m-2)
2000
Eddy
covariance
1600
Bottom-up
model
1200
Soil
inventory
800
400
Wood inventory
0
-400
2002
2003
2004
2005
20
courtesy of W. Kutsch
Fragen
•
Wie kann man "aktiven" Kohlenstoff definieren?
•
Wo befindet sich weltweit der meiste "aktive" Kohlenstoff in
Bezug auf
–
–
Ökosysteme?
geographische Region?
•
Was sind "schnelle" und "langsame" C-Flüsse?
•
Wie sieht ein typischer Jahresgang von RECO, GPP und NEP aus:
– Buchenwald
– Winterweizen
– Kartoffel
21
Soil organic matter
22
Soil organic matter
Contents:
• Relevance and chemical composition of soil organic matter
• Decomposition of soil organic matter
• Stabilization mechanisms
23
Relevance and composition of soil organic matter
24
Soil organic matter – Definition
Organic matter = „Dead material of plant or animal origin
(including anthropogenic inputs) and their decomposition
products“
• litter compounds (dead leaves, roots, hyphae)
consisting of only partly altered, non-humic substances:
lipids, proteins, carbohydrates, lignin
• humic substances (biochemically transformed litter
compounds with complex chemical structures)
NOT: living roots, living organisms
Consists of C (~50%), H, O, N, S,
and metals (Ca, Mg, Fe, Cu, Mn, Zn, Al..)
25
Why is organic matter in the soil interesting?
1. Importance for soil fertility
50% C
- nutrient store and source when mineralized
- improves water storage capacity
- improves soil aeration
- sorption of heavy metals and pollutants
Na+ K+ Mg2+ Ca2+ H+
- buffering of soil pH
- important for the soil structure (aggregation)
- reduces erosion
26
Why is organic matter in the soil interesting?
2. Carbon storage and sequestration
- CO2 assimilated by plants finally enters the soil
- soils are a huge reservoir of organic C
- a part of this carbon is mineralised again → CO2↑
but: some C remains in the soil for up to millenia
27
Composition of a typical forest soil
Hintermaier-Erhard & Zech 1997
28
Composition of
plant material
Cell wall components:
• Cellulose
- prevalent biopolymer
- chain of glucose units
• Hemicellulose
- complex polysaccharide of
sugars like xylose
• Lignin
- complex 3-dimensional structure
of phenylpropane units (C6-C3)
29
Fritsche 1998
Lignin components
Conifer
trees
1
2
3
1p-Cumarylalkohol
Coniferylalkohol
Sinapylalkohol
(x)
X
Broadleaved
trees
X
X
Grasses
X
X
X
30
Chemical composition of microbial residues
Bacterial cell wall:
- Murein (peptidoglycane)
- Lipids
- Lipopolysaccharides
Fungal cell wall:
- Protein
- Chitin (Aminosugar-polymer – n-acetylglucosamin)
- Cellulose
- other polysaccharides (mannose, glucose)
31
Chemical composition of OM entering the soil
Cellulose
Hemicellulose
European beech (Fagus sylvatica)
Wood
32
43
Leaves
Coarse
roots
Fine
roots
Bacteria
Fungi
Lignin
Proteins
Lipids
C/N
24
2
0.8
100-400
20
17
11-16
6
5
30-50
33
18
22
1.6
1.3
190
19
10
33
5.4
3.1
55
0
4-32
0
50-60
10-35
5-8
8-60
(Chitin)
2-15
0
14-50
1-42
10-15
(Scheffer-Schachtschabel 2002, Tab. 3.1-1)
32
Fragen
• Wie ist „mean residence time“ (mittlere Verweilzeit) definiert?
• Welche Kohlenstoffflüsse treten in Ökosystemen auf?
• Welche Faktoren bestimmen die Kohlenstoffbilanz von
Ökosystemen?
• Wieviel des ursprünglich durch Photosynthese aufgenommenen
Kohlenstoffs bleibt im Ökosystem?
• Wie ist organische Substanz in Böden definiert?
• Aus was besteht organische Substanz im Boden?
• Wie ist die Struktur von Cellulose, Hemicellulose und Lignin?
33
Decomposition of soil organic matter
34
Litter decomposition
German classification
KA5
L
Soil Taxonomy
WRB
Oi
Litter, Streu
Of
Oh
Oe
„Förna“
Oa
humifiziert
i: slightly decomposed OM
e: moderately decomposed OM
a: highly decomposed OM
35
Litter decomposition
Oak leave four weeks after leaf fall
Preferential decomposition of parenchymal
tissue. Woody tissue remains.
Scheffer-Schachtschabel 2002
Fungi growing on leaf tissue surface
36
Cellulose decomposition
Hydrolytic decomposition by Acomycetes:
„Weiß- und Braunfäulepilze“ = white and
brown rot fungi, aerobic and anaerobic
bacteria
Cellulose is used as energy source
Formation of body substances
Stabilisation of bacterial mucus at
mineral surfaces
37
Decomposition of lignin
• only under aerobic conditions through
unspecific oxidative radical-reaction, no
hydrolyses
• only by fungi, mainly „Weissfäulepilze“
(partly „Weichfäulepilze“)
• lignin cannot be used as only C or energy
source – Cometabolism
• Oxidative first: implementation of carbonyl-,
carboxyl-groups into the molecule: → better
dissolvable in water
• bacteria only cut methoxyl groups and some side chains but no phenols
• incomplete degradation products remain in the soil: humic substances
38
Haider 1996
Decomposition of plant material
39
Litter decomposition – Three phases
40
Cotrufo et al., in Schulze et al., 2002, Fig. 3.3.4
Fragen
• Unter welchen Umweltbedingungen wird organische
Substanz besonders schnell abgebaut?
• Welche Pflanzenteile werden schnell, welche langsam
abgebaut? Warum?
41
Soil organisms
42
Soil organisms
Megafauna
> 20 mm
Makrofauna
2-20 mm
Mesofauna
0,2-2 mm
Mikrofauna
0,02-0,2 mm
Bodenflora
< 0,02 mm
Decomposers in the soil
Organismus
Regenwurm
Fadenwürmer Milben
Bakterien
Pilze
Größe
9-30 cm
0.3-1.5 mm
0.2-0.3 mm
0.00010.0005 mm
Hyphen:
mehrere Meter
?
6-12 Monate
Teilung
alle 20 min
unbestimmt
1x1015/m²
20000km/m²
Lebensspanne 3-6 Jahre
Population
300/m²
30 Mio./m²
600000/m²
Aktivität
Bioturbation,
Fragmentierung,
Aggregatbildung,
Durchmischung von
organischer Substanz
und Mineralpartikeln
fressen
Mikrofauna,
verteilen
Bakterien,
Mineralisation
Fragmentierung, Mineralisation, Mineralisation,
Verbesserung
chemischer
chemischer
Umbau
der
Umbau
Bodenstruktur
44
Decomposition under unaerobic conditions
1. Fermentation / Gärung
• Der Energiegewinnung dienende Stoffwechselprozesse in derem Zuge
organische Verbindungen oxidiert werden
• Beispiel: Alkoholische Gärung, Milchsäuregärung
• Im Gegensatz zur Atmung bei der Zucker vollständig zu CO2 und H20
mineralisiert werden, enthalten die Abbauprodukte der Gärung noch
Energie (z.B. Ethanol, Acetet) und können weiter abgebaut werden
• Endprodukte der Gärung sind Ausgangssubstrate für die
Methanogenese im Zuge der anaeroben Nahrungskette (z.B. aus
Acetat oder H2 und CO2)
45
Fritsche 1998
Decomposition under unaerobic conditions
2. Anaerobe Atmung
• Effektivere Nutzung der im Substrat enthaltenen Energie als bei der
Gärung
• Als Wasserstoffakzeptoren dienen statt O2 beispielsweise
NO3- (Nitratatmung) → N2 / N2O
SO42- (Sulftatmung) → H2S
CO2 (Carbonatatmung) → CH4 (Methanogenese)
Insgesamt: weniger biologische Aktivität, langsamerer
Abbau, selektive Anreicherung bestimmter Substanzen wie
Lignin, Bildung von organischen Säuren, Alkoholen sowie
den Gasen CH4, H2S und N2O
46
Fragen
• Wie beeinflusst die Makro- und Mesofauna die
Geschwindigkeit des Abbaus von organischer Substanz?
47