Soil organic matter and global carbon cycling
Leibniz University Hannover ￭ Institute of Soil Science 12.2.2009 Bodenkundliches Kolloqium
Georg Guggenberger and co-workers Institute of Soil Science
Biolaitosyhdistys, Jokioinen, 6.-7. November 2013
guggenberger@ifbk.uni-hannover.de, www.soil.uni-hannover.de
Outline
- Introduction
- Mechanisms of organic matter stabilization (old and emerging concepts)
- Density fractionation as a useful tool to separate functionally different foms of organic matter
- Impact of land use on soil organic matter - Special relevance of permafrost soils - Conclusions
Climate Change
Observed and forecasted increase in temperature (IPCC, 2007, 2013)
Forecast 2090-2099 (A1B) Observed change 1901-2012
(IPCC, 2007)
Heimann (1997) Mann et al. (1999)
Long-term CO
2sinks: Weathering of silicates and carbonates
Atmospheric CO2 concentration as function of
orogenesis and following mineral weathering, e.g.
CO2 + CaSiO3
CaCO3 + SiO2
Pagani et al. (2009) Nature
The global carbon cycle in the Anthropocene
IPCC, 2000 3000 Gt C
Emission
CO2 in the atmosphere
Photosynthesis
Litter
Release
Fossil
carbon Soil humus Ocean
Respiration
Decomp.
Uptake Vegetation
Data on soil organic matter stocks are still a matter of uncertainty
Soil stores about 4 times as much C as does the atmosphere and about 5 times more C as in the whole terrestrial biomass
Small changes in the soil organic C stocks are
leading to huge response in the atmospheric
CO2 concentration
Surface C pools
Atmosphere 750 Gt Terr. Biomass 560 Gt Soil (0-100cm) 1.500 Gt (0-200cm)
(2.400 Gt) new data ca. 3.000 Gt
Schimel (1995), Stevenson (1985), Tarnocai et al. (2009)
Controlling factors of soil organic carbon stocks
Soil organic matter
= Input * turnover (steady state equilibrium)
Plant biomass
Two management options 1. Input
Land use
(- Biofuel production)
Land management
(+ Compost application)
Fertilization
Yield
2. Output versus stabilization
= Function of …
Soil tilage
Litter quality
Soil organisms
Abiotic environment
carbon sink is based on the long mean residence time of organic matter in soil
Ahe 525 a
Bh 120 a
Bhs 745 a
Bv-Cv 1570 a
Cv 3840 a
Kaiser et al. (2002) J. Plant Nutr. Soil Sci.
Foto: Karsten Kalbitz
Why is soil organic matter so old?
Mechanisms of organic matter stabilization in soil
Schmidt et al. (2011) Nature
Schmidt et al. (2011) Nature
Schmidt et al. (2011) Nature
Mechanisms of organic matter stabilization in soil
• Except for the water-soluble fraction chemical separates don‘t differ from each other and the bulk soil
Chemical
fractions differ not functionally Increase of δ13C values in different fractions as com- pared to the bulk soil after 1, 5, and 20 years of maize cultivation on a C3 soil
Increase of 13C in bulk soil [%o]
0 2 4 6 8 10
Increase of 13 C in fractions [%o]
0 2 4 6 8 10
water soluble humic acid humin fulvic acid
Y = X
Balesdent and Mariotti (1996), In: Mass Spectrometry of Soils
Schmidt et al. (2011) Nature
Mechanisms of organic matter stabilization in soil
Schmidt et al. (2011) Nature
Mechanisms of organic matter stabilization in soil
HOOC R C a b C C g
Black
Carbon Aliphatc Biopolymers Lignin
Physical separation Interaction with minerals
Chemical recalcitrance
200 nm
?
classes as determined by stable isotope approach (Six and Jastrow, 2002)
Ecosystem Aggregate size class µm MRT (years)
Tropical Macroaggregate >200 60
pasture Microaggregate <200 75
Temperate Macroaggregate 212-9500 140
pasture Microaggregate 53-212 410
Corn field Macroaggregate >250 42
Microaggregate 50-250 691
Wheat – bare fallow Macroaggregate 250-2000 27
“no till” Microaggregate 53-250 137
Wheat – bare fallow Macroaggregate 250-2000 8 “conventional till” Microaggregate 53-250 79
Biophysical stabilization in macroaggregates (manageable);
Influences organic C turnover at intermediate time scales (= decades) [turnover time of unproteced organic C is a few years]
Mechanismen der Kohlenstoffspeicherung im Boden
HOOC R C a b C C g
Black
Carbon Aliphatc Biopolymers Lignin
Physical separation Interaction with minerals
Chemical Recalcitrance
200 nm
mineral surfaces
Innersphere surface complexation (ligand exchange)
Fe, Al, Mn oxides, allophane, imogolite, edges of clay minerals
van der Waals forces Neutral siloxane surfaces
O O
C OH2+
OH
OH
OH OH
OH Mz+
OH OH OH
O C Reaction with siloxane surfaces
C O- O
Cation bridges
Negatively charged siloxane surfaces
H2 O
Organic carbon on mineral surfaces
Mikutta et al., Biogeochemistry 77, 25
100 nm A
B
Al C
Si
Fe
Intensity
A B
r2 = 0.95 r2 = 0.59
r2 = 0.25
TEM image with EDX spectra of a microaggregate from an Umbric Andosol Bw horizon
Grünewald et al., 2007, Org. Geochem.
Separation at 1,6 g cm–3
Fine earth
“free Light Fraction”
d <1,6 g cm–3
Dispersion by sonication Separation at 1,6 g cm–3
“occluded Light Fraction”
d <1,6 g cm–3
“Heavy Fraction (Mineral associated)
d >1,6 g cm–3
Density fractionation to separate functionally different organic C pools
Soil organic C stocks in different fractions
Schulze et al. (Hrsg.), 2009, CarboEurope IP.
n=10
14C age of soil organic C in different fractions
Schulze et al. (Hrsg.), 2009, CarboEurope IP.
n=10
Density fractionation to separate functionally different organic C pools
Relation between the organic C stock in the mineral- associated fraction and pedogenic oxides
Schrumpf et al. (2013) Biogeosciences Hainich
Hesse Soroe Carlow Gebesee Grignon Bugac Easter Bush Laqueuille Bordeaux Norunda Wetzstein
Alo
0 1 2 3 4
MOM C-Stock
0 1 2 3 4 5 6 7
Fed
0 5 10 15 20 25
MOM C-Stock
0 1 2 3 4 5 6 7
AlO [g kg-1] Fed [g kg-1] C stock, HF [kg m-2 ]
Pedogenic Al Pedogenic Fe
Biochemical recalcitrance Pyrogenic carbon:
Terra Preta, Chernozems and other soils of fire ecosystems Lignin (at low redox potential):
Bogs
Physical separation
Young soils (small contents in Fe, Al oxides) or soils of high biological activity:
Chernozems, Luvisols, etc.
Formation of mineral-organic associations
Soils with high contents of short-range ordered Fe, Al hydroxides Podzols, acidic Cambisols
Vulcanic soils (rich in small-range ordered allophanes) Andosols
Impact of land use on global C cycling
Earth Different continents
Until 1960s land use change was the major driver of increase of greenhouse gases in the atmosphere
Paustian et al. (2000)
Paustian et al. (2000)
Prairie soils during the 19th century
Year
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 3000
3500 4000 4500 5000 5500 6000 6500 7000 7500
Organc matter in in 20 cm soil depth (g/m²)
Conventional tillage Start of
reduced tillage
61 % of OM of 1907 First ploughing
of Prairie, 1907
53 % of OM of 1907
Law of thumb: Agriculture reduces organic matter stocks by 50%
Jenkinson et al. (2000)
Organic amendments help to increase organic carbon in soil
Impact of land management on global C cycling
No fertilizer 35t/ha org. manure
35t/ha org. manure till 1871
Changes of organic carbon concentration at different fertilization - Rothamsted Horesefield-Experiment
Körschens et al. (1998)
Organic amendments help to increase organic carbon in soil fertilization - Bad Lauchstädt Fertilization Experiment
Düngung
ohne NPK
10 t/ha a
10 t/ha a + N
PK
15 t/ha a
15 t/ha a + N
PK
Corg
[%]
0,0 0,5 1,0 1,5 2,0 2,5
Nt (%)
0,00 0,05 0,10 0,15 0,20 0,25
Corg (%) Nt (%) Col 4 Col 5
Comparison of temperate and tropical soils
Humus loss in a 65 years long cultivated Chernozem (temperate soil) (left) and a 6 years long cultivated Ferralsol (tropical soil) (right)
Soils of humic tropics loss particularly fast particulate (active) humus
With loss of organic carbon soils are loosing large parts of CEC
Highly weathered soils of the humid tropics are not suitable for agriculture
Tiessen et al. (1994) Nature
OC [Mg ha-1 (0-20 cm)]
0 20 40 60 80 100
Total-C
Min. ass.-C POM -C
98 a
Turnover time
144 a
55 a
Steppe Arable
OC [Mg ha-1 (0-20 cm)]
0 20 40 60 80 100
Total-C
Min. ass.-C POM -C
11 a
Turnover time 15 a
0.5 a
Forest Arable
pre-Colombian soils of the Amazon (Terra Preta)
Terra Preta is a tropical soil that can be used in a sustainable way
Terra Preta serves as a model for soil management in horticulture (not in large-scale agriculture)
CPMAS 13C NMR Spectra
Oxisol Terra Preta
Black C:
Turnover time: 1600 y Stock: 50 Mg ha-1
Biogenic C:
Stock: 150 Mg ha-1 Black C:
Stock: 5 Mg ha-1 Biogenic C:
Stock: 70 Mg ha-1
Glaser et al. (2001) Naturwiss.
Permafrost soils cover globally 22 Mio km2 and 65% of Russia
Store much organic matter (about. 1/2 of the the soil organic matter of the Earth)
Recent estimates (Schuur et al., 2009): 1.672 Gt
Resopond very sensitive on a temperature increase
(temperature of permafrost often only 0 to -1oC)
What happens with permafrost thaw?
… coming now to the cold climate – Permafrost soils
Discontinuous (10-90%) Continuous (>90%) Sporadic (<10%)
Research area
Permafrost thaws:
Thicker active layer
Temperature increase of permafrost
Disappearance of permafrost
Igarka
Microcatchment Little Grawijka Creek at Yenisei river
P3
P6 P7
P3 P7
P6
Rodionov et al. (2007) Eur. J. Soil Sci.
Rodionov et al. (2007) Eur. J. Soil. Sci.
-200 -150 -100 -50 0
Fibristel
active layer
Perma- frost
26 + 329 kg C m-2 -200 -150 -100 -50 0
Haplorthel
30 + 30 kg C m-2 -200 -150 -100 -50 0
Haplocryept
8 kg C m-2
For comparison:
Terrestrial soils (0-100 cm) in Germany: ca. 10 kg C m-2 Bogs (0-200 cm) in Germany: ca. 150 kg C m-2
-120 -80 -40 0
CH4 flux (g m-2 )
Methane fluxes between soils and atmosphere
Flessa et al. (2008) Global Change Biol.
Net methane uptake from August to November P4
P1 P3 P5 P6
Permafrost soils No permafrost
CH 4 flux (mg m-2 )
Terrestrial soils of the forest tundra are methane sinks
Soils with permafrost (net uptake ca. 1.5 kg CH4 ha-
1 a-1)
Soils without permafrost (net uptake ca. 0.5 kg CH4 ha-1 a-1)
Subhydric soils;
Partly with floating grass mats
P7 Blodau et al. (2008)
J. Geophys. Res. Atmosph.
Methane emission from thermokarst lake
Flessa et al. (2008) Global Change Biol.
Methane exchange between thermokarst lake and the atmosphere
0 5000 10000 15000
15-Jul 13-Oct 11-Jan 11-Apr 10-Jul
frozen
?
CH
4(µg m
-2h
-1)
Thermokarst lakes are strong methane sources
Flessa et al. (2008) Global Change Biol.
Methane flux: July 2006-August 2007
Thermo- karst
area Soils
without
Soils with permafrost CH 4 flux (mg m-2 )
permafrost
Soils with Permafrost
Thermokarst
-50 0 50 100 150 200 250
Cumulative Methane fluxes – absolute within the catchment
Flessa et al. (2008) Global Change Biol.
-20 0 20 40 60
Area percentage of catchment
-40 0 40 80 120
Methane flux (kg year -1)
Methane fluxes in the 0.44 km2 catchment area
Thermokarst
represents only 2% of the catchment, but controlls the methane emission
Decisive question:
How much organic carbon will be
mobilized as CO2 and as CH4 in
permafrost areas?
Conclusions
- Humus (soil organic matter) is the largest active carbon pool on the world
- Small changes of this pool will result in large changes of atmospheric CO2 (and CH4)
- Soil organic matter storage is largely controlled by
environmental conditions; changes in the environmental conditions likely will lead to a mobilization of carbon
- Arable land use represents a globally significant carbon source
- Degraded soils (depleted in organic matter) can be managed as carbon sink
- Permafrost soils likely represent the largest risk with respect to climate change (positive feedback reactions)
Thank you very much!
Litter
Modified Litter
Microbial Residues
Dissolved Organic Matter
Recalcitrance
Interactions with mineral phase
Physical separation
