The interactions between soil biota, soil structure, and SOM … · 2016-10-31 · The interactions...
Transcript of The interactions between soil biota, soil structure, and SOM … · 2016-10-31 · The interactions...
The interactions between soil biota,
soil structure, and SOM dynamics
Leibniz University Hannover ■ Institute of Soil Science
12.2.2009 Bodenkundliches Kolloqium
Georg Guggenberger, Florian Carstens([email protected])
KEYSOM – 1st Training School
Coimbra, October 4-7, 2016
Stabilisierung organischer Substanz im BodenContents
1) The global carbon cycle on a geologic time scale
2) Soil carbon cycling and soil structure as affected by soil biota:
• Large Herbivores, bioturbating mammals
and termites
• Earthworms
• Roots, fungi and bacteria
Biogenic
aggregate
Stabilisierung organischer Substanz im BodenRole of soils in the global carbon cycle
CO2 in atmosphere
780 Gt C (+3.3 a-1)Emission
6.3 Gt C a-1
Photosynthesis
120,7 Gt C a-1
Vegetation
600 Gt C
Respiration
60 Gt C a-1
Release
90 Gt C a-1
Uptake
92.3 Gt C a-1
Decomp.
60 Gt C a-1Litter
60 Gt C a-1
+ 0.7
Gt C a-1
Fossil
carbonSoil OM
ca. 3000 Gt COcean
39000 Gt C
Stabilisierung organischer Substanz im BodenAtmospheric CO2 content over the last 40 million years
Zh
an
g e
t a
l., 2
01
3
The global cooling over the last 50 million years can be partly attributed to a
massive reduction of atmospheric CO2 content
Stabilisierung organischer Substanz im BodenSoil carbon sequestration on a geological scale
The loss of atmospheric CO2 was mainly
caused by:
• lower subduction rates of carbonate-
rich marine sediments
decrease of volcanic outgassing
• mountain range formation
increase in rock weathering
StabiConclisierung organischer Substanz im BodenMycorrhiza: symbiosis of plant and fungi
with relevance for weathering
Reid (2001)
• Mycorrhizal fungi are ‘extention of
roots’
• Fungi deliver to plant water
and nutrients
Mycorrhizal fungi are involved in
OM decomposition
(ectomycorrhiza, EM) and
mineral weathering (EM and
arbuscular mycorrhiza)
• Plant supplies fungi with sugars
Stabilisierung organischer Substanz im BodenRock eating fungi – mineral weathering by mycorrhizal fungi
van Breemen et al. (2000)
SEM micrographs
A) Roots and mycelia
on granite
B) Mycelia on weathered
granite
C) Hyphae penetrating
weathered feldspar in
granite
D) Interior of feldspar
grain
E) Hyphae associated
with feldspar grain
F) Hyphae associated
with quartz grain
Plant nutrition
Mineral weathering
Soil genesis
(Earth surface
shaping)
Stabilisierung organischer Substanz im BodenMycorrhizal weathering of muscovite
Weathering of muscovite
by mycorrhizal fungi as
determined by confocal
laser microscope
Stabilisierung organischer Substanz im BodenSoil carbon sequestration on a geological scale
The loss of atmospheric CO2 was mainly
caused by:
• lower subduction rates of carbonate-
rich marine sediments
decrease of volcanic outgassing
• mountain range formation
increase in rock weathering
• sequestration of carbon in soils,
e.g. grassland soils
Chernozem
(south Siberian steppe)
Stabilisierung organischer Substanz im BodenSoil carbon sequestration on a geological scale
• The increasingly cooler, drier climate promoted the propagation of
grasslands, replacing the thermophilic forests that thrived in warmer,
more humid geologic eras
• By contributing to global cooling, the sequestration of carbon in
grassland soils played a role in further grassland expansion
http://smallfarms.oregonst
ate.edu/sites/default/files/s
qn2013_gregretallack.pdf
From Retallack, G.:
Downloaded September
30, 2016
Stabilisierung organischer Substanz im BodenGrassland expansion and organic carbon sequestration
Retallack, G. (2013) Annual Reviews of Earth and Planetray Sciences 41, 69-86.
“Similarly, global expansion of grasslands and their newly evolved, carbon-rich soils (Mollisols) over the past
40 million years may have induced global cooling and ushered in Pleistocene glaciation. Grassland evolution
has been considered a consequence of mountain uplift and tectonic reorganization of ocean currents, but it
can also be viewed as a biological force for global change through coevolution of grasses and grazers.”
Stabilisierung organischer Substanz im BodenSoil carbon sequestration on a geological scale
Sapristel
(lower Yenissei,
Siberia)
• The storage of carbon in soils has
been affecting the global climate
throughout the geologic past
• Besides grasslands, the largest
amounts of carbon are stored in
permafrost soils and peatlands
• Nowadays these soils are
turning into a carbon source!
Ruptic-histic Aquiturbel (Kolyma, Siberia)
Stabilisierung organischer Substanz im BodenSoil carbon sequestration on a geological scale
Sapristel
(lower Yenissei,
Siberia)
• The storage of carbon in soils has
been affecting the global climate
throughout the geologic past
• Besides grasslands, the largest
amounts of carbon are stored in
permafrost soils and peatlands
Ruptic-histic Aquiturbel (Kolyma, Siberia)
Stabilisierung organischer Substanz im BodenContents
1) The global carbon cycle on a geologic time scale
2) Soil carbon cycling and soil structure as affected by soil biota:
• Large Herbivores, bioturbating mammals
and termites
• Earthworms
• Roots, fungi and bacteria
Biogenic
aggregate
Regional to
profile scale
Profile to
millimeter scale
Millimeter to
micrometer scale
Stabilisierung organischer Substanz im BodenInfluence of biota on soil structure and SOM cycling
on different scales
Stabilisierung organischer Substanz im BodenLarge-scale SOM impact by mega and macrofauna
The macrofauna affects OM cycling in soils
• Large herbivores
faster biogeochemical cycling of OM
• Termites
concentrate OM by re-allocation to their mounds
• Bioturbants
mixing of soil layers and thereby OM
At the Pleistocene / Holocene transition, Siberian grass steppes disappeared and
were largely replaced by forest and moss tundra
Grazing pressure and fertilization by grazing megafauna (e.g.
Mammuthus) led to predominance of grasses in Pleistocene
Most species hunted to extinction by humans
Stabilisierung organischer Substanz im BodenEffect of large herbivores on soil OC sequestration
Tim Haines, 2000
Zimov et al. (1995); Zimov (2005)
Stabilisierung organischer Substanz im BodenEffect of large herbivores on soil OC sequestration
Zimov et al. (1995)
Arid climate Wet climate
Productive speciesSTEPPE
Unproductive speciesTUNDRA
ClimateHypothesis
Dry Soils High Evapo-transpiration
High Soil Oxygen
High rates ofMineralization
High NutrientAvailality
High LitterQuality
Low Evapo-transpiration
Wet Soils
Low Soil Oxygen
Low rates ofMineralization
Low NutrientAvailality
Low LitterQuality
Stabilisierung organischer Substanz im BodenEffect of large herbivores on soil OC sequestration
Zimov et al. (1995)
Productive speciesSTEPPE
Unproductive speciesTUNDRA
Dry Soils High Evapo-transpiration
High Soil Oxygen
High rates ofMineralization
High NutrientAvailality
High LitterQuality
LargeGrazers
FecesUrine
Surfacedisturbance
Lowdisturbance
LowHerbivory
HerbivoryHypothesis
Low Evapo-transpiration
Wet SoilsHumanHunting
Low Soil Oxygen
Low rates ofMineralization
Low NutrientAvailality
Low LitterQuality
Stabilisierung organischer Substanz im BodenEffect of large herbivores on soil OC sequestration
Zimov et al. (1995)
Arid climate Wet climate
Productive speciesSTEPPE
Unproductive speciesTUNDRA
ClimateHypothesis
Dry Soils High Evapo-transpiration
High Soil Oxygen
High rates ofMineralization
High NutrientAvailality
High LitterQuality
LargeGrazers
FecesUrine
Surfacedisturbance
Lowdisturbance
LowHerbivory
HerbivoryHypothesis
Low Evapo-transpiration
Wet SoilsHumanHunting
Low Soil Oxygen
Low rates ofMineralization
Low NutrientAvailality
Low LitterQuality
Stabilisierung organischer Substanz im Boden
The macrofauna affects OM cycling in soils
• Large herbivores
faster biogeochemical cycling of OM
• Termites
concentrate OM by re-allocation to their mounds
• Bioturbants
mixing of soil layers and thereby OM
Large-scale SOM impact by mega and macrofauna
Stabilisierung organischer Substanz im BodenTermites: Effects of carbon cycling
•
• Horizontal allocation of OM
• Termites concentrate and process OM in their mounds
Beckmann, 1987
Stabilisierung organischer Substanz im BodenTermite mounds in Africa
Photos: Reinhold Jahn
Stabilisierung organischer Substanz im BodenTermites: Effects of carbon cycling
Reviewed in Bonachela et al. (2015);
Siebers et al. (2015)
Tree-dominated mounds in Sofala,
Mozambique, taken from helicopter
(from Bonachela et al., 2015)
Termite mounds:
• promote water infiltration
• are enriched in OM and nutrients
Ecological hot spots
supporting rich plant
assemblages and the
associated animals, especially
relevant in dry seasons
Termite mounds buffer
ecosystems against
desertification
Stabilisierung organischer Substanz im BodenTermite mounds: landscaping
Light detection and ranging
(LIDAR) hillshade image
of termite mounds in
South Africa’s Kruger
National Park
Termite mounds on
Bangweulu
floodplain, Zambi
Banchela et al. (2015)
Stabilisierung organischer Substanz im BodenOrganic matter translocation and depodsolization by ants
Outside of nest Underneath
of nest
Underneath of nest
20 years after
abandonment
Kristiansen und Amelung (2001)
Stabilisierung organischer Substanz im Boden
The macrofauna affects OM cycling in soils
• Large herbivores
faster biogeochemical cycling of OM
• Termites
concentrate OM by re-allocation to their mounds
• Bioturbants
mixing of soil layers and thereby OM
Large-scale SOM impact by mega and macrofauna
Stabilisierung organischer Substanz im BodenGrassland soils: Vertical OM allocation by bioturbation
• In steppe climates, there is an annual surplus of OM production
• In the moist spring months, more OM is produced by the vegetation than
can be decomposed in the dry summer and cold winter months
• Therefore, OM is enriching in soils and grasslands, thus becoming a
significant sink for atmospheric carbon dioxide
South Siberian steppe
Stabilisierung organischer Substanz im BodenGrassland soils: Vertical OM allocation by bioturbation
The extension of grasslands into relatively moist
climate is enabled by large herbivores, which cause
a selective advantage of grasses over woody plants
wikimedia commons
• OM production is related to annual precipitation
• Transport of SOM by bioturbation
• Deep A horizons rich in OM
Stabilisierung organischer Substanz im BodenGrassland soils: Vertical OM allocation by bioturbation
typical signs of
bioturbation:
Krotowina (russ.
Крот = mole)
(filled hollows of
burrowing mamals)
Stabilisierung organischer Substanz im BodenGrassland soils: Vertical OM allocation by bioturbation
Ivanov and Khokhlova (2008)
Model profile of chernozem
Mean of 200 profiles from the central
chernozemic region of Russia:
1: 12C in % of soil (upper 10cm = 100%)
2: 12Cha in % of the soil,
3: 12C in % of Corg
Mean of radiocarbon datings from 46
samples:
4: 14C in 14Cha in % of the soil
5: MRT (mean residence time) in ka
6: K% of the soil
Increase in radiocarbon
age with soil depth
Stabilisierung organischer Substanz im BodenDeep soil OM: more and older
Jobbagy and Jackson (2000)
Depth Global SOC stock (Pg)
0-1 m 1,300-1,600
1-2 m 500
2-3 m 350
Below 40 cm ~ 50%
Below 20 cm ~ 80%
Permafrost below 30 cm
>800
Relevance of OM translocation
to subsoil:
Globally, most soil organic carbon is below 50 cm, but only
few studies look below 30 cm
• Most deep soil organic
carbon is very stable
• Since we do not know
why it is stable, we
cannot predict
vulnerability to change
(Torn et al. 2009)
… but of course also other
processes contribute to organic
matter accumulation in subsoil
Regional to
profile scale
Profile to
millimeter scale
Millimeter to
micrometer scale
Stabilisierung organischer Substanz im BodenInfluence of biota on soil structure and SOM cycling
on different scales
Stabilisierung organischer Substanz im BodenImportance of environment and biota for soil organic matter
Schmidt et al. (2011)
(plus bioturbation)
Stabilisierung organischer Substanz im BodenEarthworm burrows
• Epigeics transform litter on the soil surface
• Endogeics ingest large amounts of soil; mostly horizontal burrows
• Anecics mix surface litter with soil; mostly vertical burrows
• Burrow walls: high OM content hot spots for microbial activity
• Burrows promote air and water infiltration into soils
Stabilisierung organischer Substa nz im BodenEarthworm burrows create hot spots
Tomography of
earthworm burrows
• Earthworm burrows are sites of high microbial activity (hot spots)
75
50
25
0
0 1 2 3
S.E.
soil carbon [% C]
soil matrix
preferential flow paths
depth
[cm
]
0 50 100 150 200 250
S.E.
Cmic
[mg kg-1]
soil matrix
preferential flow path
0 25 50 75
DNA [mg kg-1]
0.0 0.5 1.0
DAPI counts [1010
cells kg-1]
Parameters of microbial activity along
preferential pathwas
Bundt et al. (2001a, b)
H.-J. Vogel
Stabilisierung organischer Substa nz im BodenEarthworm casts
• Mixtures of soil and OM decomposed in earthworm guts
• Can be easily processed by bacteria and fungi
Earthworm activity increases the amount of bacteria and fungi
Royal Earthworm
Society of Britain
Stabilisierung organischer Substa nz im BodenEarthworm activity: Stabilization of organic matter
in aggregates vs. release of CO2
OM is protected in microaggregates
in casts, burrow linings, and middens
Lubbers et al., 2013
Earthworm activity leads to C mineralization
release of CO2, N2O
Stabilisierung organischer Substa nz im BodenImpact of earthworms on organic carbon stocks
Earthworm biomass correlates with OC stocks
Relationship between earthworm biomass
and total soil C across 16 farms in the
western Sacramento Valley, California
Furthermore, residue management options are relevant
Earthworm activity increases SOM
(Tomato) mulch
enhances earth-
worm acitivity
Fonte et al. (2009)
Stabilisierung organischer Substa nz im BodenEarthworm cast: indication of organic matter stabilization
• Earthworm casts are enriched in easily available organic matter
protected within aggregates
Size classes (mm) of water-stable aggregates of earthworm cast and
surrounding soil
Guggenberger et al. (1996)
Sample 8-5 3-3.15 3.15-2 2-1 1-0.5 0.5-0.2 <0.2
Earthworm cast 494 27 188 22 3 2 3
Surrounding soil 168a 222b 201 192c 100d 57e 56f
Casts Soil Casts Soil Casts Soil
Dry weight (g kg-1 soil) 415 406 272 159a 313 406b
C content (g kg-1) 35.0 2.8a 63.3 32.1b 57.8 43.0c
(ac/al)V 0.22 0.39 0.47 0.80 0.62 1.10a
(Hexoses/Pentoses) 0.52 0.28a 1.19 0.94 1.89 2.38b
Sand (0.2-2 mm) Silt (2-20 µm) Clay (< 2µm)
Characteristics of OM associated with earthworm cast and surrounding soil
Stabilisierung organischer Substa nz im BodenBiogenic aggregates versus physiogenic aggregates
Fresh
cast
• Under pasture casts are enriched in fine particulate organic matter and
microaggregates mixed with fine materials
Earthworms can directly initiate the formation of microaggreagtes with
concomitant stabilization of organic matterPulleman et al. (2005)
Welded
cast
Intermediate
fractionPhysiogenic
aggregae
Impact of earthworm activity on soil macro- and microaggregates and OM
incorporation under different farming systes
Pasture 47.6 % 29.9 % 22.6 %
Conventional 7.4 % 25.5 % 66.0 %
tillage
Regional to
profile scale
Profile to
millimeter scale
Millimeter to
micrometer scale
Stabilisierung organischer Substanz im BodenInfluence of biota on soil structure and SOM cycling
on different scales
Stabilisierung organischer Substanz im BodenMean residence time of different biomolecules
Schmidt et al. (2011)• No individual compound appears to be recalcitrant!
Stabilisierung organischer Substanz im BodenChange in paradigm of organic matter stabilization
Schmidt et al. (2011)• Active stabilization of biomolecules is necessary
Stabilisierung organischer Substanz im BodenStabilization processes of organic matter in soil
• Biota is involved in stabilization of OM by physical separation
and interactions with minerals
HOOC RbCC C
a g
BlackCarbon
Aliphatc Biopolymers Lignin
Physical separation Interaction with minerals
Chemical recalcitrance
200 nm
StabiConclisierung organischer Substanz im BodenRole of biota in OM stabilization within aggregates
Bingham
et al. (2016)
The pathway from plant residue input over microbial decomposition processes
to spatial separation of OM in soil aggregates.
StabiConclisierung organischer Substanz im BodenConcept of formation of biogenic aggregates
Julie Jastrow
CONCEPTUAL DIAGRAM OF AGGREGATE HIERARCHYFrom Jastrow and Miller, 1998, In Soil Processes and the Carbon Cycle, CRC Press.
Particulate organic
matter colonized by
saprophytic fungi
Mycorrhizal hyphae
Plant and fungal debris
Silt-sized microaggregates
with microbially derived
organomineral associations
Clay microstructures
Pore space; polysaccharides
and other amorphous
interaggregate binding agents
Microaggregates
~ 90-250 and 20-90 m
Plant root
CONCEPTUAL DIAGRAM OF AGGREGATE HIERARCHYFrom Jastrow and Miller, 1998, In Soil Processes and the Carbon Cycle, CRC Press.
Particulate organic
matter colonized by
saprophytic fungi
Mycorrhizal hyphae
Plant and fungal debris
Silt-sized microaggregates
with microbially derived
organomineral associations
Clay microstructures
Pore space; polysaccharides
and other amorphous
interaggregate binding agents
Microaggregates
~ 90-250 and 20-90 m
Particulate organic
matter colonized by
saprophytic fungi
Particulate organic
matter colonized by
saprophytic fungi
Mycorrhizal hyphaeMycorrhizal hyphae
Plant and fungal debrisPlant and fungal debris
Silt-sized microaggregates
with microbially derived
organomineral associations
Silt-sized microaggregates
with microbially derived
organomineral associations
Clay microstructuresClay microstructures
Pore space; polysaccharides
and other amorphous
interaggregate binding agents
Pore space; polysaccharides
and other amorphous
interaggregate binding agents
Microaggregates
~ 90-250 and 20-90 m
Microaggregates
~ 90-250 and 20-90 m
Plant rootPlant root
StabiConclisierung organischer Substanz im BodenMycorrhiza: symbiosis of plant and fungi
with relevance for soil aggregation
Reid (2001)
• Mycorrhizal fungi are ‘extention of
roots’
• Fungi deliver to plant water
and nutrients
Mycorrhizal fungi are involved in
OM decomposition
(ectomycorrhiza, EM) and
mineral weathering (EM and
arbuscular mycorrhiza)
• Plant supplies fungi with sugars
Parts of OM is fungal derived
Hyphaea together with plant
roots are enmeshing soil
particles, forming aggregates
StabiConclisierung organischer Substanz im BodenThe role of mycorrhizal fungi for soil organic matter
Glomalin (mg g-1
)
0 1 10
Ag
gre
gate
sta
bilit
y (
%)
-20
0
20
40
60
80
100
120
r2 = 0.86, p <0.001, n = 37
Y = 42.7 + 61.3 x log10
IREEG
Mid-Atlantic states
IllinoisTexas
MinnesotaScotland
Glomalin, a glycoprotein on hyphae
of arbuscular mycorrhizal fungi on
the surface of soil aggregates
(Wright, 2002)
Relationship between extractable glomalin
and water-stable aggregates (1-2 mm)
(Wright and Upadhyaya, 1998)
• Increases with soil age
• Has a mean residence time
of decades
• Represents 1-20% of SOC• AM fungi foster soil
aggregation
StabiConclisierung organischer Substanz im BodenAggregate formation: Role of soil fungi
(both saprotrophic and mycorrhizal)
Bacteria and fungi
on wheat straws
Fungal hyphaelinking soil particles
Chenu and Stotzky (2002)
Besides plant roots, fungal hyphae can play a significant role in binding soil
particles together to form larger aggregates
StabiConclisierung organischer Substanz im BodenAggregate formation: Role of fungi
Mean weight diameter (MWD) determined by fast
wetting (FW), mechanical breakdown (MB), and
slow wetting (SW) pre-treatments
Different letters indicate differences (p < 0.001)
Impact of residues and plants on aggregates
4 combinations: with/without plant growth (wheat)
with/without wheat residue addition
addition of residues and the
presence of plants with active
roots increased the presence of
all aggregation agents
most important aggregating
agents: Soluble carbohydrates
and fungal activity linked to
production of glomalin type
proteins
Carrizo et al. (2015)
StabiConclisierung organischer Substanz im BodenFormation of small microaggregates by bacteria
Chenu and
Stotzky (2002)
Cryo-TEM of bacterial microaggregate
StabiConclisierung organischer Substanz im BodenFormation of mineral-organic associations
Chenu and Stotzky (2002)
• Bacteria, minerals and OM can form mineral-organic composites
• Attachment of bacteria onto minerals can proceed via electrostatic attraction,
hydrophobic interaction, and by cellular excretions
• Microbial exudates increase aggregate stability
StabiConclisierung organischer Substanz im BodenSoil aggregates as analysed by TEMF
oste
r (1
98
8)
A, amoeba; B, bacteria; C, clay mineral(s); CW, cell wall; CWR, cell-wall remnant; F, fungal hypha (vesicular-arbuscular mycorrhizal?);
1t0, humified organic matter; M, mucigel; PP, polyphenols; P, pore; Q, quartz grain (site of); E, egg; FE, faecal pellet; L, lysis zone in mucigel
StabiConclisierung organischer Substanz im BodenEvidence of soil fauna and plant residues in soil aggregation
Left: Crack filled with excrements of Enchytraeidae;
Right: Organic residues in the aggregated soil matrix.
Dark-field illumination. Scale bar: 200 µm.
Rasa et al. (2012; thin sections and images by Thilo Eickhorst) University of Bremen
Soil Microbial Ecology
Dr. Thilo Eickhorst
Fluorescence microscopic ob-
servations of microaggregates
ReviTec site in
Ngaoundéré (Cameroon).
A: Microaggregate, consisting of very
fine organic and mineral material and
colonised by bacteria;
B: Fungi are part of microaggregates
C: Organo-mineral complexes
consisting of plant debris colonized by
bacteria.
#1: Fluorescent images after double
excitation
#2: Fluorescent images after UV
excitation for the visualization of DAPI
stained microorganisms.
Scale bar: 50 μm.
Schnee and Eickhorst (2016 in prep.)
StabiConclisierung organischer Substanz im BodenVisualization of microbial colonization
Soil aggregates (1-2 mm) packed at different bulk densities (1.3 g/cm³ left, 1.5 g/cm³
right) and inoculated with Pseudomonas fluorescens and Bacillus subtilis;
visualization of microbial colonization in the undisturbed soil matrix after DAPI
staining (blue dots) in polished sections after resin impregnation.
Juyal, Otten and Eickhorst (2016 in prep.)
StabiConclisierung organischer Substanz im BodenFISH-detected microorganisms in soil microaggregates
Left: FISH-stained bacteria (green dots) and autofluorescing fungal hypha and soil
matrix (red); right: FISH-stained fungi (green hyphae) and soil matrix (red).
CLSM images (maximum intensity projections of z-stacks). Scale bar: 50 µm.
Eickhorst (2016, in prep.)
StabiConclisierung organischer Substanz im BodenFISH-stained bacteria in soil microaggregates
Left: Microaggregate stabilized by fungal hypha (autofluorescence); Scale bar: 50 µm.
Right: Bacterial cluster colonizing a soil microaggregate. Scale bar: 20 µm.
Note: Images represent hot spots; a lot of similar aggregates were less colonized.
CLSM images (maximum intensity projections of z-stacks).
Eickhorst (2016, in prep.)
StabiConclisierung organischer Substanz im BodenBonding of minerals to bacteria
E. coli
Goethite
Montmorillonite
Kaolinite
Adsorption at edges,
not at basal surfaces
Almost no aggregate
formation
Tightly adsorbed at edges
and basal surfaces
In agreement with DLVO
(electrostatic & van der Waals
interactions)
Huang et al. (2015)
StabiConclisierung organischer Substanz im BodenMicrobial necromass as source of OMS
ch
urig
et al. (
20
13
)
Scanning electron micrographs of
soil particles (64 years; site 6) with
cell-envelopes
Soil development of the Damma glacier chronosequence
Coverage with bacterial fragments
C, N, C/N
C
N C/N
• Microbial cell-wall fragments are
an important soil organic matter
fraction
Increasing age
StabiConclisierung organischer Substanz im BodenAggregation at clay-sized scale:
Abiotic and biotic glues
100 nmA
B
Al
C
Si
Fe
Inte
nsity
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
• Soil dispersion often does not give true primary particles but microaggregates
• Not much is known about gluing agents: abiotic versus biotic
Mikutta et al. (2006)
StabiConclisierung organischer Substanz im BodenRelevance of aggregate hierarchy for OM storage
OC concentrations and C/N and C/P ratios in differentaggregate size classes
• Larger aggragates contain more OC due to additional OM in
interaggregate space (= organic glue)
Soil Site Aggregate size OC [mg g-1] C/N C/P
Mollisol Native 2000-8000 µm 35 12 n.d.grasland 500-2000 µm 34 11 113Nebrasca 300-500 µm 30 10 99
208-300 µm 25 10 8490-208µm 24 9 8453-90 µm 20 9 74<53 µm 20 9 75
Alfisol Soybean 1000-2000 µm 23 11 n.d.Missouri 500-1000 µm 18 9 n.d.
250-500 µm 18 9 n.d.100-250 µm 22 8 n.d.<100 µm 12 7 n.d.
Alfisol Arable land 1000-4000 µm 24 16 n.d.France 250-1000 µm 14 11 n.d.
50-250 µm 11 12 n.d.<50 µm 7 9 n.d.
Co
mp
iled
by G
ug
ge
nb
erg
er
(20
02
)
StabiConclisierung organischer Substanz im BodenRelevance of aggregate hierarchy for OM stabilization
Mean residence time of OC in macro and microaggregates ofdifferent ecosystems as assessed by the C4/C3 approach
• Microaggregates are efficiently stabilizing organic matter by
physical separation of the substrate from decomposing microorganisms
Ecosystem Aggregate µm MRT (yr)
size class
Temperate pasture Macroagg. 212-9500 140
Microagg. 53-212 412
Corn Macroagg. >250 14
Microagg. 50-250 61
Corn Macroagg. >250 42
Microagg. 50-250 691
Wheat-fallow, NT Macroagg. 250-2000 27
Microagg. 50-250 137
Wheat-fallow, CT Macroagg. 250-2000 8
Microagg. 50-250 79
Average ± SE Macroagg. 42 ± 18
Microagg. 209 ± 95
Co
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by S
ix a
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Ja
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(20
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StabiConclisierung organischer Substanz im BodenConcept of formation of biogenic aggregates
Julie Jastrow
CONCEPTUAL DIAGRAM OF AGGREGATE HIERARCHYFrom Jastrow and Miller, 1998, In Soil Processes and the Carbon Cycle, CRC Press.
Particulate organic
matter colonized by
saprophytic fungi
Mycorrhizal hyphae
Plant and fungal debris
Silt-sized microaggregates
with microbially derived
organomineral associations
Clay microstructures
Pore space; polysaccharides
and other amorphous
interaggregate binding agents
Microaggregates
~ 90-250 and 20-90 m
Plant root
CONCEPTUAL DIAGRAM OF AGGREGATE HIERARCHYFrom Jastrow and Miller, 1998, In Soil Processes and the Carbon Cycle, CRC Press.
Particulate organic
matter colonized by
saprophytic fungi
Mycorrhizal hyphae
Plant and fungal debris
Silt-sized microaggregates
with microbially derived
organomineral associations
Clay microstructures
Pore space; polysaccharides
and other amorphous
interaggregate binding agents
Microaggregates
~ 90-250 and 20-90 m
Particulate organic
matter colonized by
saprophytic fungi
Particulate organic
matter colonized by
saprophytic fungi
Mycorrhizal hyphaeMycorrhizal hyphae
Plant and fungal debrisPlant and fungal debris
Silt-sized microaggregates
with microbially derived
organomineral associations
Silt-sized microaggregates
with microbially derived
organomineral associations
Clay microstructuresClay microstructures
Pore space; polysaccharides
and other amorphous
interaggregate binding agents
Pore space; polysaccharides
and other amorphous
interaggregate binding agents
Microaggregates
~ 90-250 and 20-90 m
Microaggregates
~ 90-250 and 20-90 m
Plant rootPlant root
StabiConclisierung organischer Substanz im BodenRole of bacteria in aggregate destabilization
Fe
(III)SOM
Under reducing conditions: soil bacteria such as Geobacter spec.
dissolve iron oxides by using them as electron acceptors
Soil bacteria can dismantle aggregates cemented by iron oxides
Regelink et al. (2015)
Small microaggregates (1-10 µm)
• mostly controlled by Fe-(hydr)oxides,
smaller role of OM
• Fe-(hydr)oxides attached to clay and silt
adsorption sites for OM
StabiConclisierung organischer Substanz im BodenRole of bacteria in aggregate destabilization
Fe
(III)SOM
Schwertmann (1991), Lovley et al. (1998), Ryan and Gschwend (1990, 1992)
Under reducing conditions: soil bacteria such as Geobacter spec.
dissolve iron oxides by using them as electron acceptors
Soil bacteria can dismantle aggregates cemented by iron oxides
e-
StabiConclisierung organischer Substanz im BodenRole of bacteria in aggregate destabilization
Schwertmann (1991), Lovley et al. (1998), Ryan and Gschwend (1990, 1992)
Under reducing conditions: soil bacteria such as Geobacter spec.
dissolve iron oxides by using them as electron acceptors
Soil bacteria can dismantle aggregates cemented by iron oxides
SOM
Fe(II)
StabiConclisierung organischer Substanz im BodenRole of bacteria in aggregate destabilization
Schwertmann (1991), Lovley et al. (1998), Ryan and Gschwend (1990, 1992)
Under reducing conditions: soil bacteria such as Geobacter spec.
dissolve iron oxides by using them as electron acceptors
Soil bacteria can dismantle aggregates cemented by iron oxides
Significantly accelerated by
dissolved OM functioning
as electron shuttle
Fe
(III)
e-
SOM
DOM
StabiConclisierung organischer Substanz im BodenRole of bacteria in aggregate destabilization
Schwertmann (1991), Lovley et al. (1998), Ryan and Gschwend (1990, 1992)
Under reducing conditions: soil bacteria such as Geobacter spec.
dissolve iron oxides by using them as electron acceptors
Soil bacteria can dismantle aggregates cemented by iron oxides
Significantly accelerated by
dissolved OM functioning
as electron shuttle
Fe
(III)
e-
SOM
DOM
Fe
(III)
e-
StabiConclisierung organischer Substanz im BodenRole of bacteria in aggregate destabilization
Lovley et al. (1999)
Acceleration of microbial
(Geobacter metallireducens)
iron oxide reduction by soil
humic acids and AQDS, a model
quinone compound
StabiConclisierung organischer Substanz im BodenRole of bacteria in aggregate destabilization
Lovley et al. (1998)
Soil aggregates cemented by Fe
oxides can be destabilized from
the inside by iron-reducing
bacteria
By using dissolved OM as electron shuttle, iron-reducing bacteria such as Geobacter can access Fe(III) and other metals occluded in tight pore spaces that they otherwise could not reach
Stabilisierung organischer Substanz im BodenConclusions 1
1. Biota is responsible for the formation of organic matter
2. Further, it is responsible for the stabilization of organic matter
in soil, working at different scales
• Regional scale: Redistribution, acceleration of organic mattercycling and increase in soil fertility, creation of hot spots
• Soil profile scale: Input of organic matter into the subsoil(bioturbation, rhizosphere input), where organic matter is stabilized
• Aggregate scale: Active formation of aggregates with physicaldisconnection of substrate and decomposers
• Small microaggregate scale (there are not many individual particlesat clay-size scale): Active and passive formation of organo-mineral associations with binary and ternary complexes
Stabilisierung organischer Substanz im BodenConclusions 2
Change of paradigm from dominance of non-targeted
abiotic processes in aggregate formation and organic
matter stabilization to a biotic control
With the formation of soil structure, biota is shaping its
soil environment according to its needs
Soil biota is much better soil engineer than we are!
Just compare the carbon stabilization by soil biota and
our efforts of climate-change mitigation
Thank you
Stabilisierung organischer Substanz im BodenGroup tasks
1. In which ecosystems and how do large herbivores impact
soil organic matter and nutrients? Discuss also the role of
different densities of the animals.
2. Where in the soil do you expect hot spots and where cold spots?
What are the consequences for organic matter and nutrient
cycling?
3. How would you analyse the contribution of mycorrhizal fungi,
saprotrophic fungi and bacteria to aggregation and soil organic
matter storage?
4. Which processes may lead to the destabilization of organic
matter? (a) OM in permafrost soils; (b) OM in Mollisols; (c) OM
sorbed to pedogenic Fe-oxides; (d) OM in subsoil horizons. Hint:
In any case it must be associated with changing environmental
conditions.