Carbon in Physical Fractions and Organic Matter Chemical Composition of an Acrisol after Amazon Forest Burning and Conversion into Pasture

The aim of this study was to investigate impacts of Amazon Forest (AF) fire and conversion to pasture on carbon accumulation in particle size fractions and organic matter (OM) composition of an Acrisol. Soil samples were collected (0.00-2.00 m depth) in three sites: native AF (NAF); AF under natural regeneration for two years after burning (BAF); 23-years old Brachiaria pasture after AF burning (BRA). Assuming NAF area as reference, BAF and BRA areas showed negative carbon balance when carbon emitted to the atmosphere at AF burning is taken into account. Soil OM aromaticity and hydrophobicity, assessed via ¹³C nuclear magnetic resonance, in BRA and BAF were similar to that in NAF. Fire and post-fire land use altered the carbon distribution in sand, silt and clay along the soil profile and seem to have affected organo-mineral and OM self-assemblage interactions, since the relation between total soil carbon and carbon in clay was asymptotic in BAF and linear in NAF and BRA.

Keywords:
clay; saturation; deep stocks; aromaticity; ¹³C NMR

Authorship

Otávio A. Leal ^**e-mail: otavioleal@hotmail.com

Instituto Federal Catarinense (IFC), 88965-000 Santa Rosa do Sul-SC, BrazilInstituto Federal Catarinense (IFC)BrazilSanta Rosa do Sul, SC, BrazilInstituto Federal Catarinense (IFC), 88965-000 Santa Rosa do Sul-SC, Brazil

http://orcid.org/0000-0003-2786-4119

Deborah P. Dick

Departamento de Química, Universidade Federal do Rio Grande do Sul (UFRGS), 91501-970 Porto Alegre-RS, BrazilUniversidade Federal do Rio Grande do Sul (UFRGS)BrazilPorto Alegre, RS, BrazilDepartamento de Química, Universidade Federal do Rio Grande do Sul (UFRGS), 91501-970 Porto Alegre-RS, Brazil

Falberni S. Costa

Embrapa Acre, Rodovia BR-364, km 14, 69900-970 Rio Branco-AC, BrazilEmbrapa AcreBrazilRio Branco, AC, BrazilEmbrapa Acre, Rodovia BR-364, km 14, 69900-970 Rio Branco-AC, Brazil

Heike Knicker

Instituto de Recursos Naturales y Agrobiología de Sevilla, 41012 Sevilha, SpainInstituto de Recursos Naturales y Agrobiología de SevillaSpainSevilha, SpainInstituto de Recursos Naturales y Agrobiología de Sevilla, 41012 Sevilha, Spain

João A. de Carvalho Júnior

Departamento de Energia, Universidade Estadual Paulista (UNESP), 12516-410 Guaratinguetá-SP, BrazilUniversidade Estadual Paulista (UNESP)BrazilGuaratinguetá, SP, BrazilDepartamento de Energia, Universidade Estadual Paulista (UNESP), 12516-410 Guaratinguetá-SP, Brazil

José C. Santos

Laboratório Associado de Combustão e Propulsão, Instituto Nacional de Pesquisas Espaciais (INPE), 12630-000 Cachoeira Paulista-SP, BrazilInstituto Nacional de Pesquisas Espaciais (INPE)BrazilCachoeira Paulista, SP, BrazilLaboratório Associado de Combustão e Propulsão, Instituto Nacional de Pesquisas Espaciais (INPE), 12630-000 Cachoeira Paulista-SP, Brazil

*e-mail: otavioleal@hotmail.com

SCIMAGO INSTITUTIONS RANKINGS

Embrapa Acre, Rodovia BR-364, km 14, 69900-970 Rio Branco-AC, BrazilEmbrapa AcreBrazilRio Branco, AC, BrazilEmbrapa Acre, Rodovia BR-364, km 14, 69900-970 Rio Branco-AC, Brazil

Figures | Tables

Figures (6)
Tables (4)

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Figure 1
Experimental site location within Cruzeiro do Sul municipality, Acre State, Brazil. NAF: native Amazon Forest; BAF: burned Amazon Forest; BRA: Brachiaria pasture.

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Figure 2
Precipitation (PPT) and maximum, average and minimum temperatures (Tmax, Taver and Tmin, respectively) in Cruzeiro do Sul between 2008 and 2012.

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Figure 3
Total soil carbon (C_soil) stocks distribution (in percentage) along the profile of an Acrisol under burned Amazon Forest (BAF), native Amazon Forest (NAF) and Brachiaria pasture (BRA). Values are means and bars are standard deviation.

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Figure 4
¹³C NMR spectra of organic matter from 0.00-0.05 and 0.05‑0.10 m depths of an Acrisol under burned Amazon Forest (BAF), native Amazon Forest (NAF) and Brachiaria pasture (BRA).

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Figure 5
Proportion of carbon content in sand (C_sand), silt (C_silt) and clay (C_clay) fractions in relation to the total carbon (C_soil) content of the soil in burned Amazon Forest (BAF), native Amazon Forest (NAF) and Brachiaria pasture (BRA) at (a) 0.00-0.05; (b) 0.05-0.10; (c) 0.20-0.30; (d) 0.40-0.50; (e) 0.75-1.00; and (f) 1.00-1.50 m depths. Values shown as labels are means and bars are standard deviations.

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Figure 6
Relation of carbon content in silt (C_silt) and clay (C_clay) fractions with total carbon content (C_soil) in an Acrisol under (a) burned Amazon Forest; (b) native Amazon Forest and (c) Brachiaria pasture. Bars are standard deviations.

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Table 1
Particle size distribution along the Acrisol profile

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Table 2
Total soil carbon (C_soil) and nitrogen (N_soil) contents and stocks along the profile of an Acrisol under burned Amazon Forest (BAF), native Amazon Forest (NAF) and Brachiaria pasture (BRA) (values are mean ± standard deviation)

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Table 3
Proportional distribution of carbon functional groups obtained by ¹³C NMR CPMAS and hydrophobicity index (HI) at 0.00-0.05 and 0.05-0.10 m depths of an Acrisol under burned Amazon Forest (BAF), native Amazon Forest (NAF) and Brachiaria pasture (BRA). Values were obtained from composite samples

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Table 4
Carbon and nitrogen contents in sand (C_sand, N_sand), silt (C_silt, N_silt) and clay (C_clay, N_clay) and C/N ratio in these fractions along the profile of an Acrisol under burned Amazon Forest (BAF), native Amazon Forest (NAF) and Brachiaria pasture (BRA) (values are means ± standard deviation)

Figure 1 Experimental site location within Cruzeiro do Sul municipality, Acre State, Brazil. NAF: native Amazon Forest; BAF: burned Amazon Forest; BRA: Brachiaria pasture.

Figure 2 Precipitation (PPT) and maximum, average and minimum temperatures (Tmax, Taver and Tmin, respectively) in Cruzeiro do Sul between 2008 and 2012.

Figure 3 Total soil carbon (C_soil) stocks distribution (in percentage) along the profile of an Acrisol under burned Amazon Forest (BAF), native Amazon Forest (NAF) and Brachiaria pasture (BRA). Values are means and bars are standard deviation.

Figure 4 ¹³C NMR spectra of organic matter from 0.00-0.05 and 0.05‑0.10 m depths of an Acrisol under burned Amazon Forest (BAF), native Amazon Forest (NAF) and Brachiaria pasture (BRA).

Figure 5 Proportion of carbon content in sand (C_sand), silt (C_silt) and clay (C_clay) fractions in relation to the total carbon (C_soil) content of the soil in burned Amazon Forest (BAF), native Amazon Forest (NAF) and Brachiaria pasture (BRA) at (a) 0.00-0.05; (b) 0.05-0.10; (c) 0.20-0.30; (d) 0.40-0.50; (e) 0.75-1.00; and (f) 1.00-1.50 m depths. Values shown as labels are means and bars are standard deviations.

Figure 6 Relation of carbon content in silt (C_silt) and clay (C_clay) fractions with total carbon content (C_soil) in an Acrisol under (a) burned Amazon Forest; (b) native Amazon Forest and (c) Brachiaria pasture. Bars are standard deviations.

Table 1 Particle size distribution along the Acrisol profile

Depth / m	Sand / (g kg^-1)	Sand / %	Silt / (g kg^-1)	Silt / %	Clay / (g kg^-1)	Clay / %
0.00-0.05	806	80.6	136	13.6	58	5.8
0.05-0.10	777	77.7	152	15.2	71	7.1
0.10-0.15	700	70.0	196	19.6	104	10.4
0.15-0.20	683	68.3	193	19.3	124	12.4
0.20-0.30	663	66.3	192	19.2	145	14.5
0.30-0.40	625	62.5	223	22.3	152	15.2
0.40-0.50	646	64.6	196	19.6	158	15.8
0.50-0.75	604	60.4	197	19.7	199	19.9
0.75-1.00	644	64.4	164	16.4	192	19.2
1.00-1.50	609	60.9	170	17.0	221	22.1
1.50-2.00	574	57.4	163	16.3	263	26.3

Table 2 Total soil carbon (C_soil) and nitrogen (N_soil) contents and stocks along the profile of an Acrisol under burned Amazon Forest (BAF), native Amazon Forest (NAF) and Brachiaria pasture (BRA) (values are mean ± standard deviation)

Depth / m	BAF		NAF		BRA
	C_soil	N_soil	C_soil	N_soil	C_soil	N_soil
	Content / (g kg^-1)
0.00-0.05	17.9 ± 0.1	1.4 ± 0.0	14.5 ± 0.3	1.1 ± 0.0	10.1 ± 1.4	1.4 ± 0.1
0.05-0.10	10.3 ± 1.6	0.9 ± 0.1	10.4 ± 0.8	0.9 ± 0.1	8.0 ± 0.2	0.2 ± 0.0
0.10-0.15	10.1 ± 0.4	0.9 ± 0.1	8.7 ± 0.6	0.9 ± 0.1	5.7 ± 0.4	0.4 ± 0.0
0.15-0.20	8.7 ± 0.6	0.8 ± 0.1	6.5 ± 0.1	0.7 ± 0.1	4.4 ± 0.1	0.1 ± 0.0
0.20-0.30	6.4 ± 0.3	0.7 ± 0.1	6.1 ± 0.2	0.6 ± 0.0	3.7 ± 0.0	0.0 ± 0.0
0.30-0.40	5.6 ± 0.1	0.6 ± 0.0	5.0 ± 0.1	0.6 ± 0.0	3.6 ± 0.4	0.4 ± 0.0
0.40-0.50	4.6 ± 0.4	0.5 ± 0.1	3.4 ± 0.2	0.4 ± 0.0	2.9 ± 0.2	0.2 ± 0.0
0.50-0.75	3.9 ± 0.1	0.5 ± 0.0	4.3 ± 0.1	0.4 ± 0.0	2.7 ± 0.3	0.3 ± 0.0
0.75-1.00	4.4 ± 0.2	0.5 ± 0.0	2.3 ± 0.1	0.3 ± 0.0	2.4 ± 0.1	0.1 ± 0.0
1.00-1.50	2.9 ± 0.0	0.4 ± 0.0	1.2 ± 0.1	0.2 ± 0.0	3.1 ± 0.1	0.1 ± 0.0
1.50-2.00	2.3 ± 0.1	0.4 ± 0.1	1.2 ± 0.0	0.4 ± 0.1	2.8 ± 0.1	0.0 ± 0.0
Depth / m	Stock / (Mg ha^-1)
0.00-0.05	8.3 ± 0.2	0.7 ± 0.0	7.2 ± 0.2	0.5 ± 0.0	5.4 ± 0.9	0.4 ± 0.1
0.05-0.10	6.2 ± 0.8	0.5 ± 0.0	6.3 ± 0.5	0.6 ± 0.1	5.5 ± 0.1	0.5 ± 0.0
0.10-0.15	5.6 ± 0.2	0.5 ± 0.0	4.8 ± 0.3	0.5 ± 0.1	3.4 ± 0.5	0.3 ± 0.0
0.15-0.20	5.9 ± 0.4	0.6 ± 0.1	4.3 ± 0.1	0.4 ± 0.0	3.4 ± 0.1	0.4 ± 0.0
0.20-0.30	7.8 ± 0.4	0.8 ± 0.1	7.4 ± 0.3	0.8 ± 0.0	5.0 ± 0.5	0.7 ± 0.0
0.30-0.40	7.7 ± 0.0	0.8 ± 0.0	6.6 ± 0.2	0.7 ± 0.0	4.5 ± 1.4	0.6 ± 0.0
0.40-0.50	7.3 ± 0.6	0.9 ± 0.1	5.3 ± 0.3	0.7 ± 0.0	5.6 ± 0.9	0.8 ± 0.1
0.50-0.75	16.7 ± 0.5	2.1 ± 0.1	18.0 ± 0.5	1.8 ± 0.1	10.8 ± 1.6	1.7 ± 0.1
0.75-1.00	16.5 ± 0.5	2.0 ± 0.1	9.6 ± 0.4	1.2 ± 0.0	8.9 ± 0.5	1.8 ± 0.0
1.00-1.50	23.3 ± 0.6	3.6 ± 0.3	10.0 ± 0.6	2.1 ± 0.0	27.1 ± 0.5	5.4 ± 0.2
1.50-2.00	19.9 ± 1.2	3.4 ± 0.4	10.3 ± 0.2	3.1 ± 0.7	24.1 ± 0.1	4.8 ± 0.3
0.00-2.00^a a Sum of stock values (Mg ha-1) of all soil depths.	125.2	15.8	89.7	12.4	103.6	17.4

^a
Sum of stock values (Mg ha^-1) of all soil depths.

Table 3 Proportional distribution of carbon functional groups obtained by ¹³C NMR CPMAS and hydrophobicity index (HI) at 0.00-0.05 and 0.05-0.10 m depths of an Acrisol under burned Amazon Forest (BAF), native Amazon Forest (NAF) and Brachiaria pasture (BRA). Values were obtained from composite samples

Depth / m	Area	Carboxyl C / %	Aryl C / %	O-Alkyl C / %	N-Alkyl C / %	Alkyl C / %	HI^a a Hydrophobicity index (HI) = (alkyl C + aryl C)/(O-alkyl C + carboxyl C).
0.00-0.05	BAF	9.3	17.5	35.2	9.3	28.7	1.0
	NAF	12.4	14.1	37.4	9.4	26.7	0.8
	BRA	13.9	17.6	38.0	7.8	22.8	0.8
0.05-0.10	BAF	7.9	11.6	34.1	11.0	35.5	1.1
	NAF	16.4	9.2	31.4	8.7	34.4	0.9
	BRA	7.6	15.4	44.9	9.1	22.9	0.7

^a
Hydrophobicity index (HI) = (alkyl C + aryl C)/(O-alkyl C + carboxyl C).

Table 4 Carbon and nitrogen contents in sand (C_sand, N_sand), silt (C_silt, N_silt) and clay (C_clay, N_clay) and C/N ratio in these fractions along the profile of an Acrisol under burned Amazon Forest (BAF), native Amazon Forest (NAF) and Brachiaria pasture (BRA) (values are means ± standard deviation)

Area

Depth / m

Sand

Silt

Clay

C_sand / (g kg_fraction^-1)

N_sand / (g kg_fraction^-1)

C/N

C_silt / (g kg_fraction^-1)

N_silt / (g kg_fraction^-1)

C/N

C_clay / (g kg_fraction^-1)

N_clay / (g kg_fraction^-1)

C/N

BAF

0.00-0.05

12.7 ± 0.5

0.9 ± 0.0

14.1

31.4 ± 1.1

2.3 ± 0.1

13.7

58.6 ± 1.0

5.9 ± 0.2

9.9

0.05-0.10

5.2 ± 0.6

0.4 ± 0.1

13.0

21.6 ± 1.3

1.6 ± 0.2

13.5

47.6 ± 0.6

5.0 ± 0.3

9.5

0.20-0.30

3.4 ± 1.1

0.3 ± 0.1

11.3

7.1 ± 1.4

0.6 ± 0.1

11.8

19.7 ± 0.1

2.3 ± 0.1

8.6

0.40-0.50

1.8 ± 0.3

0.1 ± 0.0

18.0

3.7 ± 0.2

0.4 ± 0.0

9.3

15.2 ± 0.2

2.0 ± 0.0

7.6

0.75-1.00

2.7 ± 0.3

0.2 ± 0.0

13.5

2.7 ± 0.0

0.3 ± 0.0

9.0

10.3 ± 0.2

1.5 ± 0.0

6.9

1.00-1.50

–

3.5^a a Standard deviation was not calculated due to sample loss. ND: not detected, below detection limit (0.01%).

0.4^a a Standard deviation was not calculated due to sample loss. ND: not detected, below detection limit (0.01%).

8.8

8.8^a a Standard deviation was not calculated due to sample loss. ND: not detected, below detection limit (0.01%).

1.4^a a Standard deviation was not calculated due to sample loss. ND: not detected, below detection limit (0.01%).

6.3

NAF

0.00-0.05

9.9 ± 0.1

0.7 ± 0.0

14.1

27.8 ± 2.9

2.2 ± 0.3

12.6

64.5 ± 0.5

6.6 ± 0.0

9.8

0.05-0.10

6.3 ± 0.6

0.5 ± 0.1

12.6

15.1 ± 0.8

1.3 ± 0.0

11.6

44.8 ± 0.5

4.9 ± 0.0

9.1

0.20-0.30

3.2 ± 0.0

0.3 ± 0.0

10.7

6.3 ± 0.2

0.6 ± 0.0

10.5

27.4 ± 0.4

3.2 ± 0.0

8.6

0.40-0.50

1.1 ± 0.7

0.1 ± 0.1

11.0

4.0 ± 0.2

0.4 ± 0.0

10.0

17.8 ± 0.7

2.3 ± 0.2

7.7

0.75-1.00

–

4.2 ± 0.0

0.4 ± 0.0

10.5

14.0 ± 0.1

1.7 ± 0.0

8.2

1.00-1.50

–

2.1 ± 0.5

0.2 ± 0.0

10.5

7.2 ± 0.4

1.5 ± 0.0

4.8

BRA

0.00-0.05

5.7 ± 1.2

0.4 ± 0.1

14.3

11.6 ± 1.0

0.9 ± 0.1

12.9

57.6 ± 0.2

6.3 ± 0.0

9.1

0.05-0.10

5.0 ± 0.5

0.4 ± 0.1

12.5

9.5 ± 1.2

0.8 ± 0.1

11.9

39.6 ± 0.8

4.7 ± 0.0

8.4

0.20-0.30

1.5 ± 0.3

0.2 ± 0.1

7.5

2.3 ± 0.3

0.3 ± 0.0

7.7

12.4 ± 0.4

2.0 ± 0.0

6.2

0.40-0.50

1.2 ± 0.1

0.2 ± 0.1

6.0

1.8 ± 0.3

0.2 ± 0.1

9.0

9.7 ± 0.1

1.8 ± 0.0

5.4

0.75-1.00

1.1 ± 0.1

0.2 ± 0.0

5.5

1.4 ± 0.0

0.3 ± 0.0

4.7

6.1 ± 0.1

1.3 ± 0.0

4.7

1.00-1.50

–

2.6 ± 0.0

0.4 ± 0.0

6.5

6.3 ± 0.8

1.3 ± 0.1

4.8

^a
Standard deviation was not calculated due to sample loss. ND: not detected, below detection limit (0.01%).

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Carbon in Physical Fractions and Organic Matter Chemical Composition of an Acrisol after Amazon Forest Burning and Conversion into Pasture

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[1] *e-mail: otavioleal@hotmail.com