1. No category

a
SOM fractionation methods as
related to functional groups
and stabilization mechanisms
Luisella Celi1, Chiara Cerli2, Daniel Said-Pullicino1, Eleonora Bonifacio1
1
University of Turin, DIVAPRA, Torino, Italy
2 University of Amsterdam, Amsterdam, The Netherlands
[email protected]
Barcelona June 27-30, 2011
Introduction
SOIL ORGANIC MATTER
is a continuum of compounds
SOM decomposition and stabilisation
Introduction a
Rate = f ([S], [E], pH, T, O2, H2O)
Substrate
Inherent degradability
Intrinsic recalcitrance
Occlusion into aggregates
Physical inacessibility
Water limitation
Impossibility of S or E to migrate
Chemical interaction with minerals
Chemical protection
Migration in subsoil horizons
Enzyme limitation
Introduction a
CO2
Uncomplexed
C
Aggregate turnover
uncomplexed C into
macroaggregates
unprotected C
CO2 sorption
CO2
physically
C associated to
microaggregates
chemically
stabilised C
Condensation
CO2
Recalcitrant C
biochemically
stabised C
Adapted from Six et al., 2002
Introduction a
SOM TURNOVER
CO2
Active
Unprotected
MRT = 1/K1
intermediate
Physically
MRT = 1/K2
passive C
Chemically
MRT = 1/K3
Recalcitrant
MRT = 1/K4
Soil organic matter turnover
DECOMPOSITION
MRT = f (1/k1, 1/k2, 1/k3,1/k4….)
AB I LI ZATI O N
SoilS Tfunctionality
soil fertility
OXIDATION DEGREE OF ORGANIC COMPOUNDS
pedogenesis
Introduction a
The continuum of organic matter is not assessable
we need
to isolate and separate SOM
into organic pools
with respect to their specific
functions and turnover
Methods a
Approaches to isolate and separate OM pools
Chemical extraction methods
Extraction with NaOH and Na4P2O7
Chemical degradation methods
Sequential degradation of OM with oxidants (H2O2, KMnO4,
NaClO,…)
Destruction of the mineral phase by HF
Physical separation methods
Fractionation of aggregates according to size
Particle size separation after physical destruction of
aggregates
Density fractionation
Chemical Methods
Chemical extraction methods
Classical extraction with NaOH and Na4P2O7
Principle: separation based on different
solubility of pools characterized by similar
charge to mass ratio
Goal: bring SOM pools into solution based on
their different degree of fragmentation and
oxidation
METHOD
Chemical Extraction
SOIL
Water extractable OM
H 2O
NaOH
Na4P2O7
SUPERNATANT 30-80% of TOC
Humin
HCl
Non extractable OM
Humic acid
insoluble HS
Fulvic acid
soluble HS
OXIDATION DEGREE OF HUMIC SUBSTANCES
CHEMICAL COMPOSITION
WEOM
Chemical Extraction
WEOM, FA and HA differ for their
chemical composition
degree of depolimerisation and oxidation
FA
HA
HA
Solution-state 13C NMR
Celi et al., 2010
CHEMICAL COMPOSITION
WEOM
Chemical Extraction
WEOM, FA and HA differ for their
chemical composition
degree of depolimerisation and oxidation
Lignin derived-phenol oxidation degree
A
G
E
Solution-state 13C NMR
A
G
E
Mineral hor.
HA
HA
Organic hor.
FA
Cerli et al., 2008
SOIL FUNCTIONALITY
Chemical Extraction
Kirovsky district
40 km SE of St. Petersburg
0
10
20
40
65
a
SOIL FUNCTIONALITY
FA = f [soil(Ac/Al)V]
Chemical Extraction
HA = f [soil(Fe+Al)DCB]
SOIL (Ac/Al)V
0.2
0.4
0 CA
10 Oi
10 Ac
10 C
20 Oi
20 Oe/Oa
20 AE
20 BC
20 C
40 Oi
40 Oe
40 Oa
40 EA
40 Bs
40 BC
40 C
60 Oi
60 Oe
60 Oa
60 E
60 Bhs
60 BC
60 C
0.6
0.8
1.0
SOIL Fe+Al
1.2
0.2
0.4
0.6
DCB
(weight % soil)
0.8
1.0
1.2
0 CA
10 Oi
10 Ac
10 C
20 Oi
20 Oe/Oa
20 AE
20 BC
20 C
40 Oi
40 Oe
40 Oa
40 EA
40 Bs
40 BC
40 C
60 Oi
60 Oe
60 Oa
60 E
60 Bhs
60 BC
60 C
0
10
FA and HA production is related to
SOM decomposition and mineral
20
30
40
50
60
0
10
20
30
40
weathering
FA (OC % TOC)
50
60
HA (OC % TOC)
Celi et al., 2008
Chemical Extraction
NaOH/Na4P2O7 extraction replaces H+–bridges
within organic compounds by Na+ and disrupts
polyvalent cation bridges between OM and soil
minerals
hydrolysis involves organo-mineral and organoorgano interactions
Na4P2O7 disperses soil particles
This method simultaneously separates OM pools
stabilised by different processes leading to nonhomogenous fractions with respect to their turnover
TURNOVER
Chemical Extraction
Increase of δ13C in
different fractions
after 1, 5 and 20 yrs
of maize cultivation
on a former C3 soil
Balesdent and Mariotti, 1996; modified by G. Guggenberger, 2009
Chemical fractions, but WEOM, do not differ with respect
to their turnover
Chemical Methods
Chemical degradation methods
Degradation of OM with oxidants (H2O2, KMnO4, NaClO,…)
Principle: separation based on preferential and/or
sequential removal of OM from soil
Goal: mimic biodegradation separating less protected
OM from OM pools linked to mineral phase
Chemical Methods
Chemical degradation methods
Destruction of minerals by HF
Principle: separation based on preferential dissolution
of minerals
Goal: separate uncomplexed OM from OM pools
associated to mineral phase
METHOD
Chemical degradation
SOIL
oxidant
Uncomplexed OM
residue
removed OM
26 – 96% of TOC
Recalcitrant OM
residual OM
HF
Mineral-associated
OM
Released OM
STABILISATION DEGREE OF ORGANIC MATTER
Chemical degradation and turnover
Uncomplexed OM
14C
age
more modern
Chemical degradation
Oxidation-resistant OM
14C
age
older
Reviewed by Von Lützow et al., 2007
SOIL FUNCTIONALITY
100
2.00
+ HF
80
1.60
60
1.20
40
0.80
20
0.40
Feox (g Kg-1)
+ NaClO
organic C (% TOC)
Chemical degradation
Bw Bs Bs Bsm
0
0.00
oxidised
podzolisation
recalcitrant
mineral-associated
Bonifacio et al., 2011
less protected OM decreases with the binding strength of
organo-mineral associations
intrinsic recalcitrance explains short-term stabilisation
Mineral-associated OM increases and correlates to Fe oxides
CHEMICAL COMPOSITION
Chemical degradation
Mikutta et al., 2006
NaClO removed primarily 14C-modern OM
Recalcitrant OM is constituted mainly of aliphatic and O-alkyl
moieties
Lignin is not contained significantly in mineral-associated or
recalcitrant OM → lignin is not a long-lived component of OM
PRO/CONTRA
Chemical Methods
Classical OM fractionation based on different solubility in
NaOH, Na4P2O7 and HCl
gives functionally OM pools sensitive to soil type and
pedogenetic processes
separates small to heterogeneous macro/supramolecules
However this method simultaneously separates OM pools
stabilised by different processes leading to non-homogenous
fractions with respect to their turnover
Degradation methods are suitable to discern among different
stabilisation mechanisms
However oxidative procedures are still hardly comparable due
to different methodological parameters ([oxidant], time, T, … )
Incomplete oxidation
Physical Methods
Physical separation methods
aim at relating more directly
soil structure and function of OM
by separating OM pools with different physical surroundings
Uncomplexed OM
Unprotected (LIGHT FRACTION)
Occluded (in aggregates)
Primary organomineral complexes
<2 m
clay-sized
2-20 m
silt-sized
20-2000 m sand-sized
Secondary organomineral complex
<20 m microaggregates
20-250 m small macroaggregates
>250 m macroaggregates
Physical Methods
Particle size separation
Particle separation after physical destruction
of aggregates
Principle: separation based on dispersion of
primary particles by ultrasonication or dispersant
Goal: to obtain differently sized
organomineral complexes with a
structure and function
primary
specific
C DISTRIBUTION
Particle size separation
Enrichment of C and N in the finer soil particles
Guggenberger 2002
Sand-sized <10%TOC silt –sized 20 -40% TOC
clay-sized 50 -75% TOC
C DISTRIBUTION AND TURNOVER
turnover
Particle size separation
Hagedorn et al., 2005
PRO/CONTRA
Particle size separation
Particle size separation
Isolates well functionally
defined pools
However
Does not separate OM but soil particles
Soil dispersion often does not give true primary
particles but aggregates
Re-flocculation of primary particles after dispersion
Structure of soil is not considered
Physical Methods
Aggregate separation
Principle: separation based on dispersion of
secondary particles by wet and dry sieving
Goal: to separate OM in
differently sized
secondary organomineral complexes
METHOD
Aggregate separation
SOIL
Wet sieving
<250
2000-250
m
NaPT
m
Ultrasonication
Uncomplexed LF
residue
Ultrasonication
2000-250
250 - 20
<20
250 - 20
STABILISATION DEGREE OF ORGANIC MATTER
<20
Aggregate separation
C DISTRIBUTION
6
25
Increase of C in the
smaller aggregates
5
20
4
3
15
2
10
1
0
m <20
M <20
m 250-20
M 250-20
M 2000-250
LF
5
Said-Pullicino et al., unpublished data
C/N Ratio
C distribution (mg C g-1 soil)
NF_S
Microaggregates
protected in
macroaggregates are
richer in C than
separated
microggregates
C/N decreases from
uncomplexed
unprotected (LF) to
m<20 m
PRO/CONTRA
Aggregate separation
Separation of aggregates
Isolates functional pools based on aggregate hierarchy
Microaggregates stabilise oxidised OM
However
lack of standardization / time consuming
does not separate OM but soil aggregates
Re-flocculation of particles after dispersion
Pools isolated by aggregate fractionation have formed by
different, simultaneously acting stabilisation mechanisms
Useful pre-treatment to obtain more homogeneous fractions
Physical Methods
Density separation
Principle: separation based on different density
between uncomplexed OM and associatedmineral OM
Goal: to separate free uncomplexed OM from
OM associated to mineral phase
METHOD
Density separation
SOIL
Density solution 1.6 g cm-1
residue
Uncomplexed LF
Ultrasonication
Floating material
Uncomplexed
Occluded
Mineral
associated
Floating material
residue
STABILISATION DEGREE OF ORGANIC MATTER
CHEMICAL COMPOSITION
Density
separation
Chemical
Extraction
(Ac/Al)
V
0C
Free, occluded uncomplexed
OM differ from mineral
associated OM
10 Ac
10 C
20 AE
20 BC
20 C
MOM is more stabilised and
more oxidised
40 EA
40 Bs
More oxidised OM
accumulates into minerals
with time
40 BC
40 C
60 E
60 Bhs
60 BC
60 C
Free Uncomplexed OM
Occluded uncomplexed OM
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Mineral associated OM
Cerli et al., 2008
SOIL FUNCTIONALITY
Density separation
SOIL Fe+AlOXALATE (weight % soil)
0.0
0.2
0.4
0.6
0.8
1.0
0 CA
10 Oi
10 Ac
10 C
20 Oi
20 Oe/Oa
20 AE
20 BC
20 C
40 Oi
40 Oe
40 Oa
40 EA
40 Bs
40 BC
40 C
60 Oi
60 Oe
60 Oa
60 E
60 Bhs
60 BC
60 C
mineral associated OM
increases with formation of Fe
and Al oxides
0.0 0.1 0.2 0.3 0.4 0.5
MOM (OC % TOC)
Cerli et al., 2008
PRO/CONTRA
Chemical Methods
Separation by density
Isolates unprotected or occluded uncomplexed OM
from associated pools
OM is increasingly stabilised by interaction with
minerals
Is suitable to study OM cycling and turnover
However
lack of standardisation
1.6 g cm-3 seems the most suitable density
Crucial step: ultrasonication energy for separating
occluded OM (test)
Useful pre-treatment to obtain more homogeneous
fractions
CONCLUSIONS
Various approaches isolate
•different operationally defined OM fractions
•often show a structural or functional bias
Choice of method depends on question
A hypothesis-based combination of methods is
the most effective approach to obtain meaningful
process-oriented
results,
useful
for
understanding OM dynamics and turnover in
various ecosystems
Conclusion a
COMPARISON
CO2
Active
intermediate
Unprotected
MRT = 1/K1
Physically
MRT = 1/K2
passive C
Chemically
MRT = 1/K3
Recalcitrant
MRT = 1/K4
Chemically/recalcitrant
NaOH/P2O7
Oxidant /HF
uncomplexed
Particle size
uncomplexed
Chemically/recalcitrant
Aggregate
uncomplexed
Chemically/recalcitrant
Density
Unprotected
physically
chemically
recalcitrant
Chemically/recalcitrant
Thanks to
you for attention
C. Cerli,
D. Said-Pullicino
E. Bonifacio
for collaboration
COST FP 0803
for invitation
METHOD
WEOM
Density separation
H2O
SOIL
Density solution 1.6 g cm-1
Uncomplexed LF
Floating material
residue
?
QUESTION