Soils in fire-prone ecosystems –

Where does all the charcoal go?

Instituto de Recursos Naturales y Agrobiología de Sevilla,

CSIC, Adva. Reina Mercedes, 10, 4012 Sevilla, Spain

Heike Knicker

Pausas J.G. & Ribeiro E. 2013. The global fire-productivity relationship. Global Ecol. & Biogeogr. 22: 728-736

Global Fire Map

September, 2004

July 2004 Duration: 2 weeks Area: 26 000 ha (2.5 ha min-1)

April, 2006

Sierra de Aznalcollar Southern Spain

The Impact of Fire on the Landscape

Long Term Impact?

….If Black Carbon has been produced since the last

glacial maximum via biomass burning at the same rate

as it is now produced, BC should account for 25 – 125% of the total

soil organic carbon pool……

(Masiello and Druffel, 2003)

Where does all the charcoal go?

Post-fire runoff, Victorian Alps, Australia.

Image courtesy of Rob Ferguson and Stefan Doerr

Erosion with Post-Fire Runoff

Photo Greg Smith

Deposition and Accumulation in Sediments

DEPOSITS

Photo Greg Smith

Ozean

Recent Paddy Field: river sediment

Ancient Paddy Field : flood deposits (3320 BP)

Prehistoric Rice Field: loess (6280 BP)

Parent Material: loess

Burrying under Sediments (Fossil Paddy Soils, China, Yangtze River)

(Cao et al., Naturwissenschaften, 93, 232-236, 2006)

Ditch around a Neolithic Settlement (Murr, Southern Germany)

Schmid et al., Soil Science 166, 569-584, 2001

Charcoal as New Litter Layer

Cambisol, Central Spain, 24 years after the last fire

Cambisol, Central Spain,

2 years after the last fire

Incorporation into newly formed humus?

Former Charcoal Production Site Rio de Janeiro, Brazil

Burnt site 24 years after the last fire

Unburnt site

- Difference in color → Difference in chemistry and soil properties

- Changes in C-concentration (depends on fire conditions)

- C-sequestration potential of soils

- Soil organic matter (SOM) quality

Cambisol, Central Spain

The Impact of Charcoal on Soil Organic Matter

Solid-State Nuclear Magnetic Resonance Spectroscopy

non-degradative technique

(Chemical shift)

• Qualitative Information: Assignment of signals

• Quantification: Signal intensity

Alkyl O/N-Alkyl

Aromatic Carboxyl

200 100 0 300 -100 ppm

Solid-State Nuclear Magnetic Resonance (NMR) Spectroscopy

Alkyl

O/N-Alkyl

Aromatic Carboxyl

200 100 ppm

0 300 -100

Alkyl

O/N-Alkyl

Aromatic Carboxyl

200 100 ppm

0 300 -100

Unburnt Cambisol (Aznalcollar, Spain)

Burnt (3 weeks) Cambisol (Aznalcollar)

• Considerable difference between “natural” and “pyrogenic” SOM

• Identification of PyOM by aromatic C content

(unburnt soils < 25%)

(according to Sergides et al., 1987)

Common Model for Black Carbon (Soot)

O

O

O

O

O

O

O

C = O

CH3 O

C O

O C

O HOCH2

C O

O

O

O

O

C

O

C

(CH2)13 OH

CH3 CH

C

C H C

H

0.29 nm

C O C

O

O

O O

O

O H

O

H - C - H

H - C - H O

C C O O

O HO

C O C

O

O O

C C O O

H - C - H H - C - H

H/C = 0.48

Barbeque charcoal

?

• Electrical conductivity disables NMR spectroscopy

• Atomic H/C ratio is too low for biochars

H/C < 0.2

H/C PyOM > H/CBC-Model

(Knicker et al., 2005, Org. Geochem. 36, 1359-1377)

Maximal cluster size for PyOM: 4-6 rings

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Barbeque charcoal

Charcoal after a forest fire

Charcoal of peat

Condensate, ash (BC-Model)

Ato

m. H

/C

H/C of Charcoals

High Variability of PyOM Composition

Barbeque char

Wood-PyOM (350°C, 12 min)

200 100 0 300 -100 ppm

Alkyl O/N-Alkyl

Aromatic Carboxyl

(Knicker et al., Geoderma, 2007)

C / N (atom)

142

400

Grass-PyOM (350°C, 4 min)

Peat-PyOM (350°C, 3 min)

200 100 0 300 -100 ppm

Alkyl O/N-Alkyl

Aromatic Carboxyl

C / N (atom)

33

8

• PyOM ≠ PyOM • Occurrence of “Black N”

Alkyl O/N-Alkyl

Aromatic Carboxyl

200 100 0 300 -100 ppm

C recovery:

79%

Atm. H/C

1.1

0.8

13

172

146

130 114

55

22

73 (C-a,b,g)

115 115

115

135

145

148

56

C H 2 O H

O

R

O C H 3

8 min, 450°C 16

30 s, 350°C

0.6

8 min, 350°C

0 s, 350°C

OH OH

- Dehydroxylation

- Demethylation

- Cleavage of side chains

0.8

75%

45% - Cleavage of ether bonds and dehydroxylation of ring - Formation of biphenyls

(Knicker et al., 2008, Org.Geochem. 39, 935)

Charring of Lignin (5-20% of Plant C)

Charring of Proteins (1-20% of Plant C)

Casein:

Recovery:

C:

29%

450°C/4 min

Alkyl O/N-Alkyl

Aromatic Carboxyl

200 100 0 ppm 300 -100

Atomic C/N

4.0

N: 23%

5.2

Pyridine

Nitrile Pyrrole

Amide

Amino

* *

0 -100 -400 ppm -200 -300

-260

-347

13C NMR 15N NMR

19

Recovery:

C:

66%

350°C/4 min

N:

51% 5.1

22

156

-233

HNOC-CH-R

l

NH2

HNOC-R

Knicker, H. (2010) Organic Geochemistry, 41, 947-950.

New Conceptual Model of PyOM

135 N H

R

H N

N N H

2,5-Diketopiperazine

H2 C O

O

157

51 166

51

21

153

OH

CH3

115

130

4-Hydroxytoluene

136

123

108

117

Pyrrole

Imidazole

Pyridine

136

123

150

Indole

124

121

122

111

120

139

CH2 N

H N

N

O O Benzofuran

145 Pyranone

152

143

117

162

122

O 125

123 128

156 112

OH

OCH3

OCH3

OH

Lignin backbone

134

141

129

137 148

54

156 115

Benz (a) anthracene

Lignin Cellulose

Proteins

Structure depends on:

• source material • charring intensity

Knicker et al. (2008) Organic Geochemistry 39, 935-939.

Alternative Concept for Char Structure

- Char presents an heterogenous mixture of heteroaromatic structures (Knicker, 2007, Biogeochemistry 85, 91)

- High potential for biotic oxidation

Degradation by lignin-degraders ?

OH

OH

Pyrocatechol

COOH

OH

OH

Protocatechulic acids

Benzene Benzoic acid

COOH

Anthracene

Phenanthrene

4-Hydroxytoluene

CH2, Alkyl

OH

Benzoic acid

COOH

Naphthalene

Salicylic acid

COOH

OH

3-Hydroxy- benzoic acid

COOH

OH

Anilic acid

COOH

NH2

Ferulic acid

CH

OH

OCH3

CH

COOH

Vanillic acid

COOH

OH

OCH3

Phenol

OH

Biphenyl

4-Hydroxy- benzoic acid

OH

CH2, Alkyl

H

CH2CHCOOH

NH2

Tryptophane

N

Biochemical Degradation of Aromatic Structures

Under oxic conditions char is relatively quickly oxidized

161

171

Fresh

Gras-PyOM

PyOM

after 7 weeks

14%

10%

p p m 3 0 0 2 0 0 1 0 0 0 - 1 0 0

Incubation time: 7 weeks

Incubation of Grass PyOM

Alkyl O/N-Alkyl

Aromatic C Carboxyl

200 100 ppm

0 300 -100

Impact of Regeneration Time on SOM Composition (Pine, Cambisol, Central Spain)

Control

Burnt

11 21 42 25

Alkyl O/N-Alkyl

Aromatic C Carboxyl

13 28 37 22

1 year

24 years

14 35 33 18

(1982)

(2005)

C mg g-1

63

65

59

- Erosion? - Degradation?

Respicond (25°C)

soil

Incubation vessel

KOH

CO2

Multimeter

Respiration Experiments

Re

ma

inin

g C

r (

% o

f C

tota

l)

Incubation time (h)

Cr (%) =Cf*e(-kf*t)+ CS*e

(-ks*t)

R2 =0.998

0 2000 4000 6000 86

88

90

92

94

96

98

100

102

Degradation rate constant

Fast pool Slow pool

Mean Residence Time (MRT): 1/k

Respiration of a Soil without PyOM (7 month)

200 100 ppm

0 300 -100 200 100 ppm

0 300 -100 200 100 ppm

0 300 -100

Alkyl O/N-Alkyl

Aromatic C Carboxyl

control

(Leptosol 0-5 cm)

oak

pine

pine, 2x

Sierra de Aznalcóllar, S-Spain, After a Severe Fire, 2004

(Knicker et al. 2013, Soil Biology and Biochemistry, 197-198, 43-50.

oak pine pine ( 2x)

control pine 5 y

41 42 38 12 29 ± 1

92% 96% 95% 91% 94%

“slow” Pool:

Mean Residence Time (1/k) (years)

years

Knicker et al. 2013, Soil Biology and Biochemistry, 197-198, 43-50.

• MRT of PyOM is only slightly higher than MRT of SOM

• Charcoal as long-term C-sink?

3

7

21

35

8

27

2 7

21

30

7

22

0 1 5

1 4

Carbonyl Carboxyl/

Amide

Aromatics O - Alkyl N - Alkyl/OCH3 Alkyl

0 days

7 months

difference

Control

Changes of PyOM/SOM during Degradation

Knicker et al. 2013, Soil Biology and Biochemistry, 197-198, 43-50.

4

10

39

19

5

24

3

8

34

20

5

21

1 2 5

0 3

Carbonyl Carboxyl/

Amide

Aromatic O - Alkyl N - Alkyl/

OCH3

Alkyl

5 10

49

14

4

19

4 8

44

18

4

17

1 2

5

0 2

Carbonyl Carboxyl/

Amide

Aromatic O - Alkyl N - Alkyl/

OCH3

Alkyl

Pine

Oak

0 days

7 months

difference

Changes of PyOM/SOM during Degradation

Tierra Negra Andaluza

Vertisol: 1-2% Corg 14C-age: ≈ 5000 years (Prof. D. Faust, personal communication)

Former management: After-harvest burning (since Roman times)

Villamartín (Cádiz)

Tierra Negra Andaluza

Utrera (Sevilla)

200 100 0 300 -100 ppm

Alkyl O/N-Alkyl

Aromatic Carboxyl

Carom:

19%

200 100 0 300 -100 ppm

Alkyl O/N-Alkyl

Aromatic Carboxyl

Carom:

28%

Alkyl O/N-Alkyl

Aromatic Carboxyl

200 100 ppm

0 300 -100

Briquette

CORECarom 72% Ctot

If source material is known CORECarom allows determination of PYOM by using a correction factor f

Chemical Oxidation (60°C; K2Cr2O2+ H2SO4; 6 h):

COREC

88% Ctot

200 100 ppm

0 300 -100

Alkyl O/N-Alkyl

Aromatic Carboxyl

Grass-PyOM

CORECarom

33% Ctot

COREC

39% Ctot

200 100 ppm

0 300 -100

Alkyl O/N-Alkyl

Aromatic Carboxyl

Az3 (burnt)

CORECarom 20% Ctot

COREC

32% Ctot

Knicker, et al. 2007,Geoderma, 142, 178-196.

Chemical Oxidation of Tierra Negra

200 100 0 300 -100 ppm

Alkyl O/N-Alkyl

Aromatic Carboxyl

Carom:

19%

200 100 0 300 -100 ppm

Alkyl O/N-Alkyl

Aromatic Carboxyl

200 100 0 300 -100 ppm

Alkyl O/N-Alkyl

Aromatic Carboxyl

Carom:

32%

200 100 0 300 -100 ppm

Alkyl O/N-Alkyl

Aromatic Carboxyl

0 - 20 cm

20 – 40 cm

< 50 cm

Aromatic

Carom:

28%

29%

18%

200 100 0 300 -100 ppm

Villamartín (Cádiz, S-Spain) Selective enrichment of PyOM

↓

Increase of aromaticity of SOM due to removal

of fresh litter

Tierra Negra Andalucia

2 years 5 years

22 years 1 years

Chronosequence: Ceasing Biannual Burning (Planalto, Brazil)

Time after last fire:

Soil

(1 year after last fire)

0-5 cm

15-30 cm

30-45 cm

13C NMR Spectra of the A Horizon of a Leptsol from the Planalto (Brazil)

Alkyl

O/N-Alkyl

Aromatic Carboxyl

200 100 ppm

0 300 -100

• No clear indication for PyOM

Fast degradation of PyOM?

• Increase of aromatic C with depth

•Translocation? •Selective enrichment? •Humification?

Humic Leptosol

(0-5 cm): 12.1%

(15-30 cm): 6.4%

(30-45 cm): 3.7%

PyOC Stocks in Comparison with non-PyOC (0-30 cm)

2.0 1.7 1.6

19.3

20.1

17.7

14.8

0

5

10

15

20

25

0 5 10 15 20 25

PyOC

Ctot

7.4

7.1 6.7

4.5

4.3 4.4

3.5

O-Alkyl

Alkyl

years

kg

m-2

Burning leads to C increase

C increase is due to addition of carbohydrates

(input of unburnt necromass

of dead roots)

New litter input “masks” PyOM

41.1

27.8

24.8

21.3

7.1

CT: g kg-1

Ap: 0-15 cm 30

A2: 15-40 cm 39

A3: 40-70 cm

54

A5: 100-150 cm

58

Bw1: 260-300 cm

38

ppm 50 100 150 200 250 0 -50

16

19

19

24

18

C/N

PyOC in Soils under Cerrado (Viracopos)

Velaso et al. submitted

PyOM in subsoil as efficient C sink

PyOC in Soils under Cerrado

Velasco-Molina et al. in preparation

% clay silt sand

C T

-

0.86 0.30 0.59

carboxyl 0.52 0.16 - 0.55

aryl 0.36 - 0.52 - 0.01

O - alkyl - 0.46 0 .58 0.06

N - alkyl - 0.42 0.50 0.07

alkyl - 0.38 0.30 0.16

- In addition to PyOM-mineral interaction other mechanism must occur - Accumulation due to low biochemical activity?

p p m 3 0 0 2 0 0 1 0 0 0 - 1 0 0

Ah Sand: 91%

E Sand: 95%

BC (T) Clay: 52%

C1 (T) Clay: 47%

Residue after

H2O-Extraction last burning:1999

Sampling: 2002

p p m 3 0 0 2 0 0 1 0 0 0 - 1 0 0

C2 Clay: 19 % Sand: 68 %

H2O-Extract

C of Cbulk

0.8%

1.8%

2.2%

Planosol, Pantanal (Brazil)

• We have evidence for oxidation of the aromatic network On a larger time scale degradation processes may level out

the differences between PyOM and SOM in the topsoil • Once oxidized, the increasing solubility allows leaching of

PyOM to the deeper soil

High PyOM content in subsoil as a typical feature of soils with frequent char input?

Fire (biochar input) as soil forming factor?

Conclusion: PyOM in Soils

PyOM

N, P, Ca, K, Mg

Litter

Fate of PyOM in Soils

Liming effect! Fertilization!

“Masking” (Brazil, Planalto)

Selective

enrichment of

PyOM (Andalusia)

.

leaching

degradation

oxidation

Absorption to mineral phase, stabilization

Accumulation (Pantanal)

O2deficiency

Knicker, H. , 2011,Quaternary International, 243, 251-263

The Ecological Role of Black Nitrogen?

Modell of Charred Proteins

R

H N

N

2,5-Diketopiperazine (C/N: 2:1)

O

O

157

51 166

51

4-Hydroxytoluene

153

OH

CH3

115

130

CH2

H2 C

21 N H

108

117

Pyrrole (C/N: 4:1)

-235

135 N H

Pyridine (C/N: 5:1)

136

123

150

Indole (8:1)

124

121

122

111

120

139

N

-245

-90

136

123 Imidazole (C/N: 1.5:1)

N

H N

-202

-220 to

-250

13C chemical shift 15N chemical shift

Knicker, H. (2010) Organic Geochemistry, 41, 947-950.

Relative Contribution of BN to BC

Charring, 2 min, 350°C, oxic conditions

Atomic C/N: 5.1 (casein-BC)

0 -100 -400 ppm -200 -300

Pyrrole

BN ≈ 60% of Ct

Charred grass

Charred peat

Atomic C/N

8.5

39.6

BN ≈ 13% of Ct

Contribution of BN in Burnt Soils

0 -100 -400 ppm -200 -300

Pyrrole Amide

1 year (33% char )

Control (A horizon, Cambisol

Central Spain)

0 -100 -400 ppm -200 -300

Pyrrole Amide

24 years 20 % char

C/N (w/w) 25

24 years: 33% of char C = heteraromatic C (7% of Ctot)

C/N 22

1 year: 27% of char C = heteraromatic C (9% of Ctot)

Pot Experiments with 15N-PyOM

125 g dry soil + 0.5 g seeds + 150 mg 15N-enriched PyOM.

De la Rosa, J.M., Knicker, H. (2011). Soil Biology and Biochemistry, 2368-2373.

Plant Availability of PyOM -15N

0 10 20 30 40 50 60 70

10

15Nadd present in grass (%)

Incubation time (days)

Plants can use 15N of PyOM

De la Rosa, J.M., Knicker, H. (2011). Soil Biology and Biochemistry, 2368-2373.

Bioavailability of 15N-PyOM (15N NMR)

0 -100 -400 ppm -200 -300

Pyrrole Amide

Soil +15N-PyOM 72 days

Amides are newly formed from 15N-PyOM

(20% of 15Ntot)

15N-PyOM of grass

De la Rosa, J.M., Knicker, H. (2011). Soil Biology and Biochemistry, 2368-2373.

Ah Sand: 91%

E Sand: 95%

Bt1 clay: 52%

Bt2 Clay: 47%

C Clay: 19 % Sand: 68 %

200 100 0 300 -100 ppm

0 -100 -400 ppm -200 -300

Pyrrole

13C 15N

C/N = 5

Residue after removal of DOM

Almost all aromatic C is N-heteroaromatics

Planosol, Pantanal (Brazil)

Conclusions (BN)

• BN is quantitatively relevant in fire-affected soils

• BN can be biochemically degraded, providing N for the build-up of new biomass

• Peptides are precursors of Black Nitrogen

• “BN” is an important and integral part of “BC”

PyOM

N + P, Ca, K, Mg

BN as a “Slow-release” Fertilizer for Providing N after Vegetation Fires

Liming effect!

Fertilization!

leaching

N

SON cycle

Need to use heterocyclic N after fires is in contrast to a high biochemical recalcitrance!

• PyOM ≠ PyOM

• Behavoir of PyOM depends on source material and environmental conditions

• Degradability of PyOM is related with its ecological function

Low PyOM levels can be explained with:

• Transport to the Ozean • Lower biochemical recalcitrance of PyOM than thought • Leaching and accumulation in deeper soils with low

biological activity • DOM in rivers?

• The role of BN as a post-fire fertilizer should not be

underrated

Conclusions (Summary)

Thanks to: - CITIUS (University of Sevilla) - MINECO (Spain) and FEDER (CGL2009-10557/CGL2012-

37041) - IHSS for supporting the travel

Thanks for Your Attention !!!