Effects of fire on soil organic matter in northern Amazonian forest fragments

SILVA, Libério Junio da; DICK, Deborah Pinheiro; NECKEL, Djennifer; NÓBREGA, Gabriel Nuto; RODRIGUES, Renato de Aragão R.; BARBOSA, Reinaldo Imbrozio; CORDEIRO, Renato Campello

doi:10.1590/1809-4392202100133

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Agronomy and Forestry • Acta Amaz. 52 (1) • Jan-Mar 2022 • https://doi.org/10.1590/1809-4392202100133 copy

Effects of fire on soil organic matter in northern Amazonian forest fragments

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Forest fires incorporate pyrogenic organic matter into the soil, affecting the characteristics of soil organic matter (SOM) due to its high aromaticity, increasing its renewal time. However, the factors that control the concentration of pyrogenic organic matter and its chemical composition and structure are still little known. Forest fragments dispersed in a savanna matrix of the northern Brazilian Amazon are frequently impacted by fires, which can affect the composition of SOM within the fragments. The aim of this study was to analyse the chemical composition of SOM in the border and interior of six forest fragments in the Roraima savanna, in the northern Brazilian Amazon. Soil samples were collected at 10-cm intervals up to 1 m in depth at the border and in the interior of each fragment. Soil organic material concentration was determined with 10% HF solution and its elemental composition, thermogravimetric index, and ¹³C CPMAS NMR spectroscopic analysis were determined. There was no significant difference in the aromaticity index between border and interior. The concentration of alkyl C structures between border (22 to 25%) and interior (19 to 29%) indicated the occurrence of medium-intensity fires in the study area. The thermogravimetric analysis showed no significant difference in the thermal stability of SOM between border and interior. Our results showed no pronounced difference in SOM quality up to 1 m depth between the border and the interior of the evaluated forest fragments, indicating that this compartment is stable throughout the fragments.

KEYWORDS:
forest fires; aromaticity index; elemental composition; FTIR

Depth (cm)	C (%)	N (%)	C/N	C_HF (%)	N_HF (%)	C/N_HF	R	I_C=C/I_C-H
Border
0-10	1.58 (0.08)	0.26 (0.01)	13 (0.16)	4.50 (1.25)	0.63 (0.01)	7.1 (1.20)	0.5	3.3
10-20	1.19 (0.28)	0.28 (0.01)	13 (1.57)	3.70 (1.20)	0.82 (0.00)	4.5 (0.70)	0.3	3.9
20-30	0.72 (0.01)	0.06 (0.00)	12 (0.21)	2.66 (0.86)	0.21 (0.00)	12.7 (1.50)	1.0	4.5
30-40	0.57 (0.00)	0.09 (0.00)	11 (0.08)	1.82 (0.26)	0.50 (0.01)	3.6 (1.10)	0.3	4.3
40-50	0.47 (0.03)	0.07 (0.00)	11 (0.63)	1.61 (0.20)	0.37 (0.00)	4.4 (0.52)	0.3	4.1
90-100	0.29 (0.01)	0.03 (0.00)	9 (0.19)	0.93 (0.12)	0.17 (0.00)	5.5 (0.81)	0.4	4.5
Interior
0-10	1.56 (0.03)	0.12 (0.01)	13 (0.25)	4.60 (1.32)	0.63 (0.03)	7.3 (1.40)	0.6	2.2
10-20	0.90 (0.05)	0.07 (0.00)	12 (0.31)	3.49 (1.16)	0.82 (0.03)	4.3 (0.44)	0.3	3.9
20-30	0.62 (0.01)	0.05 (0.00)	11 (0.01)	1.96 (0.71)	0.21 (0.00)	9.3 (1.03)	0.7	5.2
30-40	0.55 (0.06)	0.05 (0.00)	11 (0.74)	1.71 (0.68)	0.50 (0.01)	3.4 (0.90)	0.3	4.2
40-50	0.51 (0.05)	0.05 (0.00)	10 (0.73)	1.45 (0.56)	0.37 (0.00)	3.9 (0.94)	0.3	5.4
90-100	0.37 (0.02)	0.02 (0.00)	10 (0.63)	0.95 (0.14)	0.17 (0.00)	5.6 (0.80)	0.4	5.6

Attribute	Soil depth (cm)
Attribute	0-10	10-20	20-30	30-40	40-50	90-100
Border
pH	5.46 (0.43)	5.24 (0.38)	5.09 (0.36)	5.03 (0.30)	5.01 (0.32)	5.20 (0.34)
Ca⁺² (cmol_cdm^-3)	2.85 (1.22)	1.80 (0.90)	1.30 (0.74)	1.03 (0.62)	0.93 (0.45)	0.70 (0.43)
Mg⁺² (cmol_cdm^-3)	1.12 (0.49)	0.76 (0.46)	0.62 (0.20)	0.58 (0.19)	0.60 (0.26)	0.66 (0.28)
K⁺¹ (cmol_cdm^-3)	1.33 (1.01)	0.66 (0.63)	0.27 (0.12)	0.25 (0.12)	0.21 (0.09)	0.28 (0.37)
Al⁺³ (cmol_cdm^-3)	0.06 (0.11)	0.11 (0.15)	0.13 (0.15)	0.15 (0.16)	0.15 (0.17)	0.06 (0.10)
P⁺³ (cmol_cdm^-3)	11.02 (5.72)	6.55 (2.90)	4.67 (3.66)	2.23 (1.28)	1.56 (1.46)	0.30 (0.66)
SB (cmol_cdm^-3)	5.29 (2.28)	3.22 (1.43)	2.19 (0.90)	1.86 (0.70)	1.75 (0.60)	1.61 (0.95)
SOM (g kg^-1)	35.13 (6.68)	24.04 (5.11)	17.34 (5.57)	14.43 (4.55)	10.88 (2.79)	5.96 (2.97)
Sand (%)	69.60 (7.60)	66.94 (6.55)	63.18 (6.01)	59.36 (9.18)	54.32 (9.48)	46.37 (10.87)
Silt (%)	11.22 (4.35)	11.77 (4.57)	12.48 (6.78)	12.59 (5.74)	14.59 (8.90)	16.01 (5.27)
Clay (%)	19.19 (4.51)	21.29 (4.68)	24.34 (5.71)	28.06 (6.19)	31.09 (6.42)	29.29 (6.84)
Interior
pH	5.51(0.28)	5.31 (0.33)	5.20 (0.35)	5.11 (0.39)	5.14 (0.39)	5.25 (0.36)
Ca⁺² (cmol_cdm^-3)	3.00 (1.02)	1.89 (0.68)	1.21 (0.29)	0.99 (0.32)	0.93 (0.32)	0.86 (0.26)
Mg⁺² (cmol_cdm^-3)	1.00 (0.26)	0.76 (0.29)	0.68 (0.23)	0.59 (0.26)	0.64 (0.28)	0.57 (0.15)
K⁺¹ (cmol_cdm^-3)	1.24 (1.10)	0.41 (0.29)	0.29 (0.08)	0.24 (0.10)	0.21 (0.10)	0.22 (0.12)
Al⁺³ (cmol_cdm^-3)	0.03 (0.03)	0.06 (0.03)	0.08 (0.07)	0.09 (0.07)	0.09 (0.06)	0.05 (0.12)
P⁺³ (cmol_cdm^-3)	14.74 (12.22)	9.85 (5.94)	7.95 (5.41)	4.96 (2.46)	4.75 (2.58)	4.16 (2.37)
SB (cmol_cdm^-3)	5.23 (1.94)	3.06 (1.10)	2.18 (0.50)	1.82 (0.58)	1.78 (0.54)	1.52 (0.34)
SOM (g kg^-1)	38.91 (12.22)	22.65 (4.24)	14.99 (2.15)	11.50 (3.44)	9.90 (2.76)	9.09 (8.21)
Sand (%)	69.92 (6.48)	65.29 (6.90)	61.51 (8.40)	57.88 (8.89)	54.78 (9.42)	47.17 (10.37)
Silt (%)	11.26 (4.15)	12.88 (4.09)	11.96 (2.58)	11.93 (3.18)	13.15 (4.94)	14.23 (6.44)
Clay (%)	18.81(4.81)	21.84 (5.01)	26.53 (7.17)	30.19 (7.26)	32.08 (5.85)	30.27 (6.28)

Sample	Depth (cm)	Carbon types								Ratios
Sample	Depth (cm)	alkyl-C (0-45 ppm)	O-alkyl -N (45-60 ppm)	O-alkyl-C (60-90 ppm)	di-O-alkyl-C (90-110 ppm)	aromatic-C (110-140 ppm)	O-aril (140-160 ppm)	carboxyl-C (160-185 ppm)	carbonyl-C (185-220 ppm)	alkyi-C/ O-alkyl-C	arom-C/ alkyl-C
Border	0-10	22.3	14.7	26.1	9.4	12.7	5.6	8.3	0.9	0.44	0.82
Border	30-40	22.0	15.4	18.5	10.4	15.4	2.3	10.6	2.4	0.5	0.94
Border	90-100	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd
Interior	0-10	28.5	16.2	19.7	8	9.4	5.7	11.1	1.4	0.65	0.53
Interior	30-40	29.3	14.7	14.4	9.1	13.2	5.3	12.6	1.5	0.77	0.63
Interior	90-100	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd

Depth (cm)	Temperature range (°C					TGI
	30-105	105-230	230-420	420-600	Residue > 650
	Interior
0-10	0.21 (0.01)	0.21 (0.01)	2.26 (0.22)	1.55 (0.30)	95.91(1.11)	0.61
10-20	0.11 (0.00)	0.13 (0.01)	1.08 (0.33)	1.06 (0.26)	97.60 (2.20)	0.87
20-30	0.80 (0.02)	0.11 (0.00)	0.95 (0.30)	0.76 (0.12)	98.11 (3.82)	0.72
30-40	0.09 (0.00)	0.10 (0.00)	0.94 (0.28)	0.80 (0.52)	98.07 (3.24)	0.77
40-50	0.08 (0.00)	0.11 (0.00)	1.02 (0.41)	0.88 (0.46)	97.91 (4.32)	0.77
90-100	0.01 (0.00)	0.04 (0.00)	0.30 (0.30)	0.15 (0.00)	99.50 (4.81)	0.44
	Border
0-10	0.02 (0.00)	0.03 (0.00)	0.29 (0.01)	0.23 (0.03)	99.45 (2.01)	0.72
10-20	0.10 (0.00)	0.16 (0.04)	1.31 (0.14)	1.23 (0.26)	97.20 (0.90)	0.84
20-30	0.24 (0.01)	0.21 (0.13)	1.72 (0.20)	1.94 (0.42)	95.89 (1.02)	1.01
30-40	1.17 (0.02)	0.18 (0.04)	1.38 (0.32)	1.52 (0.38)	96.73 (1.70)	0.97
40-50	0.07 (0.00)	0.08 (0.00)	0.76 (0.04)	0.65 (0.24)	98.44 (2.81)	0.77
90-100	0.02 (0.00)	0.03 (0.00)	0.29 (0.02)	0.17 (0.01)	99.49 (3.92)	0.53

Location in the fragment	Depth (cm)	RI ₂₉₂₂	RI₁₇₀₅	RI₁₆₆₄	RI₁₅₄₈	RI₁₂₂₇	RI₁₀₇₇
Border	0-10	7.41	22.96	24.44	10.37	11.85	18.52
Border	10-20	6.15	18.46	23.85	14.62	14.62	18.46
Border	20-30	5.19	18.52	25.19	15.56	12.59	19.26
Border	30-40	3.95	13.16	17.11	7.89	5.26	51.32
Border	40-50	6.41	19.23	26.28	11.54	10.90	22.44
Border	90-100	6.45	15.32	29.03	12.10	2.42	32.26
Interior	0-10	6.34	21.13	14.08	14.08	11.27	18.31
Interior	10-20	6.20	17.05	24.03	10.08	12.40	26.36
Interior	20-30	4.42	18.58	23.01	13.27	13.27	24.78
Interior	30-40	6.52	17.39	27.17	13.04	8.70	23.91
Interior	40-50	5.81	13.95	31.40	13.95	6.98	24.42
Interior	90-100	4.35	13.04	24.35	10.43	5.22	40.00

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E-mail: acta@inpa.gov.br

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