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Edaphic properties in a eucalyptusforest ecotone in the Nova Baden State Park, Southeastern Brazil

ABSTRACT

State parks are integral protection units created to protect ecosystems. However, anthropic activities may have been previously performed before their creation, forming transitional areas. Studies that evaluate the modifications of edaphic properties in these environments are scarce. The aim of this study was to evaluate the changes in soil properties and litter stock in areas of eucalyptus-forest ecotones. Litter stock (Stocklitter) and total soil organic carbon content and stock (TOCsoil), weighted mean diameter (MWD), origin of aggregates (biogenic or physicogenic) and respective content of total organic carbon (TOCBio and TOCPhy), total organic carbon (TOCAG), soil organic matter chemical fractions [fulvic acid (FAC), humic (HAC), and humin (HUMC)], and particulate, mineral-associated, free light and intra-aggregate light (POC, MAOC, FLFC, and ILFC) soil organic matter, fertility, and glomalin-related soil protein (GRSP) fractions were evaluated in aggregates (layer 0.00-0.10 m) in areas of eucalyptus-forest ecotone (Eco), preserved forest fragment (For), and eucalyptus plantation (Euc), in Nova Baden State Park, Lambari–MG. In the Euc and Eco areas, the highest Stocklitter content was found. Higher values of TOCsoil, TOCAG, GRSP, and MWD were observed in the Euc area. In the biogenic aggregates, the highest content of TOCBio, HAC, HUMC, POC, MAOC, FLFC, and ILFC was determined in detriment of the physicogenic ones. The dynamics of edaphic properties in the Eco area showed greater similarity with the For area than in the Euc area. In general, all vegetation covers contribute to the maintenance of soil quality.

Keywords
accumulated litter; biogenic and physicogenic aggregates; glomalin; total organic carbon

INTRODUCTION

In Brazil, Law No. 9.985, instituted on July 18, 2000, established criteria and norms for creating, implementing, and managing Conservation Units (UCs). Since then, the conservation of areas with relevant natural resources and its management based on the preservation, maintenance, sustainable use, restoration, and recovery, within the UCs, was legitimized, ensuring the maintenance of their potential for future generations (Brasil, 2000Brasil. Lei No 9.985, de 18 de julho de 2000: Regulamenta o art. 225, § 1°, incisos I, II, III e VII da Constituição Federal, institui o Sistema Nacional de Unidades de Conservação da Natureza e dá outras providências. Brasília, DF: Ministério do Meio Ambiente; 2000. Available from: http://www.planalto.gov.br/ccivil_03/leis/L9985.htm.
http://www.planalto.gov.br/ccivil_03/lei...
). The UCs must be managed by a forest management plan, which establishes the zoning and rules for using the area and managing its natural resources (Brasil, 2000Brasil. Lei No 9.985, de 18 de julho de 2000: Regulamenta o art. 225, § 1°, incisos I, II, III e VII da Constituição Federal, institui o Sistema Nacional de Unidades de Conservação da Natureza e dá outras providências. Brasília, DF: Ministério do Meio Ambiente; 2000. Available from: http://www.planalto.gov.br/ccivil_03/leis/L9985.htm.
http://www.planalto.gov.br/ccivil_03/lei...
). The creation of this plan involves surveying the climatic, topographic, geological, pedological, and vegetation conditions of the protected area (Souza and Soares, 2013Souza AL, Soares, CPB. Florestas nativas: Estrutura, dinâmica e manejo. Viçosa, MG: Editora UFV; 2013.).

However, in some cases, UCs are established in areas where anthropic activities have been previously performed, such as the installation of monospecific plantations of exotic forest species, including eucalyptus. This is the case of the Nova Baden State Park (PENB), located in southeastern Brazil. It belongs to the category of national parks, which was established within the sphere of the state public power. This UC category belongs to the Full Protection Unit (UPI) group, which encompasses the UCs with more restrictive use. Only the indirect use of natural resources is admitted, which includes scientific research, environmental education activities, ecological tourism, and recreation in contact with nature (Brasil, 2000Brasil. Lei No 9.985, de 18 de julho de 2000: Regulamenta o art. 225, § 1°, incisos I, II, III e VII da Constituição Federal, institui o Sistema Nacional de Unidades de Conservação da Natureza e dá outras providências. Brasília, DF: Ministério do Meio Ambiente; 2000. Available from: http://www.planalto.gov.br/ccivil_03/leis/L9985.htm.
http://www.planalto.gov.br/ccivil_03/lei...
).

However, the information generated in UCs is still scarce, including the influence of eucalyptus plantations and transition areas between these plantations and native vegetation (ecotones) on soil quality. In this regard, the properties related to soil quality, nutrient cycling, and biodiversity in UPIs are included. Among these properties, we highlight those that reflect i) the relative proportion of the fraction leaves of eucalyptus, leaves of native species and/or agricultural crops (litter stock); ii) the compartmentalization of soil organic matter (SOM) and the genesis of soil aggregates (Pulleman et al., 2005Pulleman MM, Six J, Marinissen JCY, Jongmans AG. Earthworms and management affect organic matter incorporation and microaggregate formation in agricultural soils. Appl Soil Ecol. 2005;29:1-15. https://doi.org/10.1016/j.apsoil.2004.10.003
https://doi.org/10.1016/j.apsoil.2004.10...
; Vidotto et al., 2007Vidotto E, Pessenda LCR, Ribeiro AS, Freitas HA, Bendassolli JA. Dinâmica do ecótono floresta-campo no sul do estado do Amazonas no Holoceno, através de estudos isotópicos e fitossociológicos. Acta Amazon. 2007;37:385-400. https://doi.org/10.1590/S0044-59672007000300010
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; Denardin et al., 2014Denardin RBN, Mattias JL, Wildner LP, Nesi CN, Sordi A, Kolling DF, Busnello FJ, Cerutti T. Estoque de carbono no solo sob diferentes formações florestais, Chapecó-SC. Cienc Florest. 2014;24:59-69. https://doi.org/10.5902/1980509813323
https://doi.org/10.5902/1980509813323...
; Silva Neto et al., 2016Silva Neto EC, Pereira MG, Fernandes JCF, Corrêa Neto T A. Aggregate formation and soil organic matter under different vegetation types in Atlantic Forest from Southeastern Brazil. Semina. 2016;37:3927-40. https://doi.org/10.5433/1679-0359.2016v37n6p3927
https://doi.org/10.5433/1679-0359.2016v3...
; Fernandes et al., 2017Fernandes JCF, Pereira MG, Silva Neto ECA, Correa Neto TA. Characterization of biogenic, intermediate and physicogenic soil aggregates of areas in the Brazilian Atlantic Forest. Rev Caatinga. 2017;30:59-67. https://doi.org/10.1590/1983-21252017v30n107rc
https://doi.org/10.1590/1983-21252017v30...
; Schultz et al., 2019Schultz N, Pinto LASR, Lima SS, Ziviani MM, Assunção AS, Pereira MG. Agregação do solo e atributos químicos em áreas com diferentes coberturas vegetais. In: Tulio L, editor. Características do solo e sua interação com as plantas 2. Ponta Grossa: Editora Atena; 2019. vol. 2. p. 1-12. https://doi.org/10.22533/at.ed.1781917101
https://doi.org/10.22533/at.ed.178191710...
; Suárez et al., 2019; Yao et al., 2019Yao Y, Ge N, Yu S, Wei X, Wang X, Jin J, Liu X, Shao M, Wei Y, Kang L. Response of aggregate associated organic carbon, nitrogen and phosphorous to re-vegetation in agro-pastoral ecotone of northern China. Geoderma, 2019;341:172-80. https://doi.org/10.1016/j.geoderma.2019.01.036
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); and/or iii) the soil chemical properties (Pinheiro et al., 2009Pinheiro MHO, Arantes SAC, Jimenez-Rueda JR, Monteiro R. Caracterização edáfica de um ecótono savânico-florestal no sudeste brasileiro. Iheringia Ser Bot. 2009;64:15-24.).

These properties present wide variation, resulting from the interrelation between formation factors, vegetational cover, and land-use (Silva Neto et al., 2011Silva Neto SP, Santos AC, Leite LL, Dim VP, Cruz RS, Pedrico A, Neves Neto DN. Análise espacial de parâmetros da fertilidade do solo em região de ecótono sob diferentes usos e manejos. Semin - Cienc Agrar. 2011;32:541-52. https://doi.org/10.5433/1679-0359.2011v32n2p541
https://doi.org/10.5433/1679-0359.2011v3...
). We can add other aspects related to those previously mentioned, such as glomalin, configured as a glycoprotein produced by arbuscular mycorrhizal fungi (Bedini et al., 2007Bedini S, Avio L, Argese E, Giovannetti M. Effects of long-term land use on arbuscular mycorrhizal fungi and glomalin-related soil protein. Agr Ecosyst Environ. 2007;120:463-6. https://doi.org/10.1016/j.agee.2006.09.010
https://doi.org/10.1016/j.agee.2006.09.0...
; Lima et al., 2013Lima FS, Soares ACF, Sousa CS. Ocorrência e atividade de fungos micorrízicos arbusculares em plantios de eucalipto (Eucalyptus sp.) no litoral norte da Bahia, Brasil. Rev Arvore. 2013;37:245-55. https://doi.org/10.1590/S0100-67622013000200006
https://doi.org/10.1590/S0100-6762201300...
). It influences the formation and stabilization of aggregates (Hickmann et al., 2011Hickmann C, Costa LM, Schaefer CEGR, Fernandes RBA. Morfologia e estabilidade de agregados superficiais de um Argissolo Vermelho-Amarelo sob diferentes manejos de longa duração e Mata Atlântica secundária. Rev Bras Cienc Solo. 2011;35:21918. https://doi.org/10.1590/S0100-06832011000600034
https://doi.org/10.1590/S0100-0683201100...
) that can be classified in terms of their genesis, origin or formation pathways as biogenic or physicogenic.

Biogenic aggregates are formed by the activity of microorganisms, roots, and soil fauna organisms (called ecosystem engineers), whereas physicogenic aggregates arise owing to chemical factors, organic matter input to the soil, and soil wetting and drying cycles (Jouquet et al., 2006Jouquet P, Dauber J, Lagerlöf J, Lavelle P, Lepage M. Soil invertebrates as ecosystem engineers: Intended and accidental effects on soil and feedback loops. Appl Soil Ecol. 2006;32:153-64. https://doi.org/10.1016/j.apsoil.2005.07.004
https://doi.org/10.1016/j.apsoil.2005.07...
; Silva Neto et al., 2010Silva Neto LF, Silva IF, Inda AV, Nascimento PC, Bortolo L. Atributos físicos e químicos de agregados pedogênicos e de coprólitos de minhocas em diferentes classes de solos da Paraíba. Cienc Agrotec. 2010;34:1365-71. https://doi.org/10.1590/S1413-70542010000600002
https://doi.org/10.1590/S1413-7054201000...
; Loss et al., 2014Loss A, Pereira MG, Costa EL, Beutler SJ. Soil fertility, physical and chemical organic matter fractions, natural 13C and 15N abundance in biogenic and physicogenic aggregates in areas under different land use systems. Soil Res. 2014;52:685-97. https://doi.org/10.1071/SR14045
https://doi.org/10.1071/SR14045...
; Silva Neto et al., 2016Silva Neto EC, Pereira MG, Fernandes JCF, Corrêa Neto T A. Aggregate formation and soil organic matter under different vegetation types in Atlantic Forest from Southeastern Brazil. Semina. 2016;37:3927-40. https://doi.org/10.5433/1679-0359.2016v37n6p3927
https://doi.org/10.5433/1679-0359.2016v3...
; Fernandes et al., 2017Fernandes JCF, Pereira MG, Silva Neto ECA, Correa Neto TA. Characterization of biogenic, intermediate and physicogenic soil aggregates of areas in the Brazilian Atlantic Forest. Rev Caatinga. 2017;30:59-67. https://doi.org/10.1590/1983-21252017v30n107rc
https://doi.org/10.1590/1983-21252017v30...
; Suárez et al., 2019; Pereira et al., 2021Pereira MG, Loss A, Batista I, Melo TR, Silva Neto EC, Pinto LASR. Biogenic and physicogenic aggregates: formation pathways, assessment techniques, and influence on soil properties. Rev Bras Cienc Solo. 2021;45:e0210108. https://doi.org/10.36783/18069657rbcs20210108
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). In both aggregates, total organic carbon values can still be evaluated (Nichols and Wright, 2005Nichols KA, Wright SF. Comparison of glomalin and humic acid in eight native US soils. Soil Science. 2005;170:985-97. https://doi.org/10.1097/01.ss.0000198618.06975.3c
https://doi.org/10.1097/01.ss.0000198618...
; Pulleman et al., 2005Pulleman MM, Six J, Marinissen JCY, Jongmans AG. Earthworms and management affect organic matter incorporation and microaggregate formation in agricultural soils. Appl Soil Ecol. 2005;29:1-15. https://doi.org/10.1016/j.apsoil.2004.10.003
https://doi.org/10.1016/j.apsoil.2004.10...
; Loss et al., 2014Loss A, Pereira MG, Costa EL, Beutler SJ. Soil fertility, physical and chemical organic matter fractions, natural 13C and 15N abundance in biogenic and physicogenic aggregates in areas under different land use systems. Soil Res. 2014;52:685-97. https://doi.org/10.1071/SR14045
https://doi.org/10.1071/SR14045...
; Schultz et al., 2019Schultz N, Pinto LASR, Lima SS, Ziviani MM, Assunção AS, Pereira MG. Agregação do solo e atributos químicos em áreas com diferentes coberturas vegetais. In: Tulio L, editor. Características do solo e sua interação com as plantas 2. Ponta Grossa: Editora Atena; 2019. vol. 2. p. 1-12. https://doi.org/10.22533/at.ed.1781917101
https://doi.org/10.22533/at.ed.178191710...
; Ferreira et al., 2020Ferreira CR, Silva Neto EC, Pereira MG, Guedes JN, Rosset JS, Anjos LHC. Dynamics of soil aggregation and organic carbon fractions over 23 years of no-till management. Soil Till Res. 2020;198:104533. https://doi.org/10.1016/j.still.2019.104533
https://doi.org/10.1016/j.still.2019.104...
; Pinto et al., 2021Pinto LASR, Freo VA, Pereira MG, Medeiros AS, Silva CF, Santos OAQ, Souza RS. Agregação sob diferentes pedoformas em floresta estacional semidecidual, no Sudeste do Brasil. In: Santos TR, editor. Engenharia Agronômica: Ambientes Agrícolas e seus Campos de Atuação 3. ed. Ponta Grossa: Atena Editora; 2021. p. 119-33. https://doi.org/10.22533/at.ed.41121030512
https://doi.org/10.22533/at.ed.411210305...
; Pereira et al., 2021Pereira MG, Loss A, Batista I, Melo TR, Silva Neto EC, Pinto LASR. Biogenic and physicogenic aggregates: formation pathways, assessment techniques, and influence on soil properties. Rev Bras Cienc Solo. 2021;45:e0210108. https://doi.org/10.36783/18069657rbcs20210108
https://doi.org/10.36783/18069657rbcs202...
; Rossi et al., 2023Rossi CQ, Pinto LA, Moura OV, Loss A, Pereira MG. Soil organic matter in biogenic, intermediate and physicogenic aggregates under agroecological management. Rev Caatinga. 2023;36:167-76. https://doi.org/10.1590/1983-21252023v36n118rc
https://doi.org/10.1590/1983-21252023v36...
; Silva et al., 2023Silva TP, Morais IS, Santos GL, Zonta E, Pinto LASR, Fagundes HS, Pereira MG. Biogenic and physicogenic aggregates as indicators of quality in soils with sandy texture in areas of organic agriculture. Rev Bras Cienc. Solo. 2023;47:e0230007 https://doi.org/10.36783/18069657rbcs20230007
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).

In the Atlantic Forest biome, Pinto et al. (2022)Pinto LASR, Silva CF, Melo TR, Rosset JS, Pereira MG. Stability, labile organic carbon, and glomalin of biogenic aggregates in sandy soils under management systems in the subtropical region of Brazil. Rev Bras Cienc Solo. 2022;46:e0220074. https://doi.org/10.36783/18069657rbcs20220074
https://doi.org/10.36783/18069657rbcs202...
observed that biogenic aggregation provided higher levels of labile organic carbon; and contributed to increased macroaggregate stability and glomalin-related soil protein levels. This suggests an improvement in soil properties and, consequently, in soil quality. Biogenic aggregation can be considered a more sensitive, efficient, economical and reliable indicator for assessing soil quality in different soil and environmental conditions (Pereira et al., 2021Pereira MG, Loss A, Batista I, Melo TR, Silva Neto EC, Pinto LASR. Biogenic and physicogenic aggregates: formation pathways, assessment techniques, and influence on soil properties. Rev Bras Cienc Solo. 2021;45:e0210108. https://doi.org/10.36783/18069657rbcs20210108
https://doi.org/10.36783/18069657rbcs202...
).

In this context, the study formulated the general hypothesis that the assessment of soil quality through the analysis of its biological, chemical and physical properties can contribute to underpin the management plan of protected areas (UCs), and help in decision-making for the conservation and recovery of native biodiversity, which could indicate —or not— the removal of eucalyptus plantations. To test the general hypothesis, the study aimed to evaluate: i) the litter stock; ii) total soil organic carbon; iii) stability, classification, total organic carbon, organic matter fractions, fertility, and glomalin in aggregates in areas of eucalyptus-forest ecotones, preserved forest fragments, and eucalyptus plantations in PENB, which is located in the municipality of Lambari, Minas Gerais, Brazil.

MATERIALS AND METHODS

Geographical characterization of the study area

The study was conducted at PENB, which has a total area of approximately 215 ha, located in the municipality of Lambari, state of Minas Gerais, between meridians 45° and 46° W and parallels 21° 30’ and 22° S. The PENB is part of a large remaining fragment of Atlantic Forest, limited by the Serra das Águas de Lambari and the Biological Reserves of Santa Clara and Engenho Velho, located in the municipalities of Cambuquira and Campanha, respectively, in Minas Gerais (Figure 1).

Figure 1
Geographic location of the study area - Nova Baden State Park, Lambari (Minas Gerais). Forest-eucalyptus ecotone area (a), eucalyptus area (b), and native forest fragment area (c), Southeastern Brazil.

According to Köppen classification system, the region’s climate is Cwa, i.e., humid subtropical with dry winters and hot summers (Alvares et al., 2013Alvares CA, Stape JL, Sentelhas PC, Gonçalves JLM, Sparovek G. Köppen’s climate classification map for Brazil. Meteorol Z. 2013;22:711-28. https://doi.org/10.1127/0941-2948/2013/0507
https://doi.org/10.1127/0941-2948/2013/0...
). The relative humidity is approximately 75 %, occasional frosts occur, and average annual rainfall is between 1,500 and 2,000 mm. The terrain varies from mountainous to rugged, with altitudes from 1,300 to above 1,900 m. The vegetation is distributed in the phytophysiognomies Montane Semi deciduous Forest, Alluvial Semi deciduous Seasonal Forest with Euterpe edulis, High Montane Semi deciduous Seasonal Forest, and Marshy Field with Hedychium coronarium. The predominant soil classes in the area range from Latossolo Vermelho-Amarelo (Ferralsol) in the middle and upper thirds of the elevations; Latossolo with humic A horizon in the lower portion; Gleissolo (Gleisol) in the lowlands and areas that form the plain; and Cambissolo Háplico (Cambisol) in the areas of mountainous terrain (IUSS Working Group WRB, 2015IUSS Working Group WRB. World reference base for soil resources 2014, update 2015: International soil classification system for naming soils and creating legends for soil maps. Rome: Food and Agriculture Organization of the United Nations; 2015. (World Soil Resources Reports, 106).; Santos et al., 2018Santos HG, Jacomine PKT, Anjos LHC, Oliveira VA, Lumbreras JF, Coelho MR, Almeida JA, Araújo Filho JC, Oliveira JB, Cunha TJF. Sistema brasileiro de classificação de solos. 5. ed. rev. ampl. Brasília, DF: Embrapa; 2018.).

Areas selected for the study

Three areas were selected: a well-preserved fragment of montane mixed ombrophilous forest (Forest or For); a eucalyptus plantation (Eucalyptus or Euc); and an ecotone of forest-eucalyptus plantation (Ecotone or Eco). In the Forest area, the canopy was 15–25-m high, with emergent individuals of Araucaria angustifolia (Bertol.) Kuntze and Cariniana legalis (Mart.) Kuntze reaching 30 m. In the intermediate stratum, we could observe individuals of Astronium graveolens Jacq., Cabralea canjerana (Vell.) Mart., Machaerium nyctitans (Vell.) Benth., Cecropia hololeuca Miq., Piptadenia gonoacantha (Mart.) J. F. Macbr., and Erythrina sp. L. among other species. In the understory, there were arboreal-shrubby individuals of 5 to 12 m and an herbaceous stratum with subshrubs of Piper spp. Sanchezia sp., Cyathea sp., and herbs and lianas.

In the Eucalyptus area, individuals of Eucalyptus robusta Sm. and Corymbia citriodora (Hook.) K.D. Hill and L.A.S. Johnson are predominant. With the abandonment of the area approximately 100 years ago, Cedrela fissilis Vell. and Araucaria angustifolia dominate the upper stratum, but generally with smaller sizes compared to those of the Forest area. In the intermediate stratum, we found individuals from 3 to 15 m of Euterpe edulis Mart., Alchornea triplinervia (Spreng.) Müll. Arg., Croton floribundus Spreng., Allophylus edulis (A. St.-Hil. et al.) Hieron. ex Niederl, Cupania oblongifolia Mart., Psychotria vellosiana Benth., Zanthoxylum rhoifolium Lam., and Xylopia brasiliensis Spreng. Subshrub individuals of Piper spp. and Cyathea sp. of 0.5 to 1.5 m and herbaceous Goeppertia spp. and lianas comprised the lower stratum.

In the Forest and Eucalyptus areas, a high density of epiphytes was recorded, mainly Bromeliaceae, and several species of bryophytes, lichens, and fungi on the tree trunks. In the Ecotone area, the structure and composition of native species was similar to the Eucalyptus area; however, exclusive native tree species were also present, such as Prunus sellowii Koehne, Tibouchina granulosa (Desr.) Cogn., and Coffea arabica L. and a lower density of E. robusta and C. citriodora. Table 1 shows the chemical and physical soil properties of the evaluated areas.

Table 1
Chemical and physical properties of the soil in the 0.00–0.10 m layer in the study areas, Southeastern Brazil

Collecting litter and soil

Sampling was carried out in May 2019, a period in which there is a reduced in pluviometric precipitation. In each area, five sampling points (replicates or pseudo repetition) were established; these were spaced by 10 m in a transect (50 m), where the circumscribed a) litter was collected using a metal collector (25 × 25 cm), and b) composite deformed and undeformed soil samples in the surface layer. The litter was dried in a forced air circulation oven (65 °C, 72 h) to obtain the average value (Stocklitter, kg ha-1). In the Eucalyptus and Ecotone areas, the relative proportion (%) of eucalyptus leaves in the litter stock was evaluated.

At each sampling point, one composite deformed soil sample was taken, made up of five simple soil samples. Totaling five composite deformed soil samples per sampling area. Each composite deformed soil sample corresponds to a replicate, collected in the 0.00–0.10 m layer, configuring 15 sampling units (three areas × five replicate). In the laboratory, they were air dried, crumbled, and passed through a 2.0-mm-mesh sieve (Teixeira et al., 2017Teixeira PC, Donagemma GK, Fontana A, Teixeira WG. Manual de métodos de análise de solo. 3. ed. rev e ampl. Brasília, DF: Embrapa; 2017.), for determination of total soil organic carbon (TOCsoil, g kg-1) via wet oxidation of soil organic matter with potassium dichromate in acid medium (Yeomans and Bremner, 1988Yeomans JC, Bremner JM. A rapid and precise method for routine determination of organic carbon in soil. Commun. Soil Sci Plant Anal. 1988;19:1467-76. https://doi.org/10.1080/00103628809368027
https://doi.org/10.1080/0010362880936802...
). Bulk density (Bd, Mg m-3) was determined in unformed samples collected using a Kopeck ring to calculate the carbon stock (StockTOCsoil, Mg ha-1), by the equation 1 (Veldkamp, 1994Veldkamp E. Organic carbon turnover in three tropical soils under pasture after deforestation. Soil Sci Soc Am J. 1994;58:175-80. https://doi.org/10.2136/sssaj1994.03615995005800010025x
https://doi.org/10.2136/sssaj1994.036159...
), found in Oliveira (2014)Oliveira PPA. Protocolo para quantificação dos estoques de carbono do solo da rede de pesquisa Pecus. São Carlos: Embrapa Pecuária Sudeste; 2014. (Documentos, 116). Available from: https://www.infoteca.cnptia.embrapa.br/infoteca/bitstream/doc/1006926/1/Documentos116.pdf.
https://www.infoteca.cnptia.embrapa.br/i...
:

Stock TOC soil = T O C soil × B d × e 10 , (Eq. 1)

in which: e is the layer thickness (cm).

Within each point, five undeformed soil samples (clods) were randomly collected to form one composite soil sample, totaling five composite soil samples per area sampled. Each composite soil sample corresponds to a replicate, collected in the 0.00-0.10 m layer, totaling 15 sampling units (three areas × five replicate). After collection, the sample units were air-dried and then subjected to sieving using 9.7-, 8.0-, and 4.0-mm mesh sieves. Aggregates retained in the two intervals of 9.7> Ø ≥8.0 and 8.0> Ø ≥4.0 were selected for the study. In the 8.0> Ø ≥4.0 mm aggregates, sub-samples were taken for evaluation of chemical properties, glomalin, and stability of aggregates.

The pH was determined in water at 1:2.5 (m:v) ratio; exchangeable Ca2+, Mg2+, and Al3+ were extracted with KCl 1 mol L-1, and determined by titrimetry; P, K, and Na+ were extracted with Mehlich-1 solution, P was determined by colorimetry, and K+ and Na+ by flame photometry; and H+Al (potential acidity) was extracted with 0.5 mol L-1 calcium acetate solution (pH 7.1–7.2) and determined by titrimetry (Teixeira et al., 2017Teixeira PC, Donagemma GK, Fontana A, Teixeira WG. Manual de métodos de análise de solo. 3. ed. rev e ampl. Brasília, DF: Embrapa; 2017.). Total organic carbon of aggregates (TOCAG) was also determined (Yeomans and Bremner, 1988).

Glomalin was quantified as glomalin-related soil protein (GRSP). The readily extractable GRSP fraction (GRSP-EE) was obtained from autoclave extraction using 20 mmol L-1 sodium citrate solution (pH 7.0) (121 °C, 30 min). The total GRSP fraction (GRSP-T) was obtained from autoclave extraction using 50 mmol L-1 sodium citrate solution (pH 8.0) (121 °C, 60 min). The GRSP fractions were quantified by the Bradford method with modifications proposed by Wright and Upadhyaya (1996)Wright SF, Upadhyaya AA. Extraction of an abundant and unusual protein from soil and comparison with hyphal protein of arbuscular mycorrhizal fungi. Soil Sci. 1996;161:575-86. https://doi.org/10.1097/00010694-199609000-00003
https://doi.org/10.1097/00010694-1996090...
, using bovine serum albumin as the standard.

Stability of the aggregates was calculated using the weighted mean diameter (MWD) of the aggregates by the wet (WW) and dry (DW) determination methods. In both methods, 25 g of the 8.0–4.0 mm aggregates were placed on top of a set of sieves of 2.0, 1.0, 0.5, 0.25, and 0.105 mm for 15 min in the Yooder apparatus (WW) and in the ROTAP apparatus with controlled speed and rotary movements with vibration (DW). Material retained on each sieve was transferred to Petri dishes and dried in an oven (105 °C, 72 h). With the mass of aggregates, we calculated the weighted mean diameter (MWDWW and MWDDW) (Teixeira et al., 2017Teixeira PC, Donagemma GK, Fontana A, Teixeira WG. Manual de métodos de análise de solo. 3. ed. rev e ampl. Brasília, DF: Embrapa; 2017.).

Aggregates of 9.7> Ø ≥8.0 mm were then taken to the laboratory, examined under a binocular stereomicroscope, and classified according to their origin or formation pathways. For this study, two classes (biogenic and physicogenic) were identified and evaluated from the morphological patterns established by Bullock et al. (1985)Bullock P, Federoff N, Jongerius A, Stoops G, Tursina T. Handbook for soil thin section description. Albrighton, England: Waine Research Publications; 1985.. This was done using a protocol adapted by Pulleman et al. (2005)Pulleman MM, Six J, Marinissen JCY, Jongmans AG. Earthworms and management affect organic matter incorporation and microaggregate formation in agricultural soils. Appl Soil Ecol. 2005;29:1-15. https://doi.org/10.1016/j.apsoil.2004.10.003
https://doi.org/10.1016/j.apsoil.2004.10...
and validated by the studies gathered by Pereira et al. (2021)Pereira MG, Loss A, Batista I, Melo TR, Silva Neto EC, Pinto LASR. Biogenic and physicogenic aggregates: formation pathways, assessment techniques, and influence on soil properties. Rev Bras Cienc Solo. 2021;45:e0210108. https://doi.org/10.36783/18069657rbcs20210108
https://doi.org/10.36783/18069657rbcs202...
. Differentiation between the aggregates was performed based on the visualization of morphological features, such as shape, size, presence of roots, porosity (Bullock et al., 1985Bullock P, Federoff N, Jongerius A, Stoops G, Tursina T. Handbook for soil thin section description. Albrighton, England: Waine Research Publications; 1985.; Pulleman et al., 2005Pulleman MM, Six J, Marinissen JCY, Jongmans AG. Earthworms and management affect organic matter incorporation and microaggregate formation in agricultural soils. Appl Soil Ecol. 2005;29:1-15. https://doi.org/10.1016/j.apsoil.2004.10.003
https://doi.org/10.1016/j.apsoil.2004.10...
; Melo et al., 2019Melo TR, Pereira MG, Barbosa GMC, Silva Neto EC, Andrello AC, Filho JT. Biogenic aggregation intensifies soil improvement caused by manunes. Soil Till Res. 2019b;190:186-93. https://doi.org/10.1016/j.still.2018.12.017
https://doi.org/10.1016/j.still.2018.12....
; Pereira et al., 2021Pereira MG, Loss A, Batista I, Melo TR, Silva Neto EC, Pinto LASR. Biogenic and physicogenic aggregates: formation pathways, assessment techniques, and influence on soil properties. Rev Bras Cienc Solo. 2021;45:e0210108. https://doi.org/10.36783/18069657rbcs20210108
https://doi.org/10.36783/18069657rbcs202...
), and subunit arrangements and junctions (Pereira et al., 2021Pereira MG, Loss A, Batista I, Melo TR, Silva Neto EC, Pinto LASR. Biogenic and physicogenic aggregates: formation pathways, assessment techniques, and influence on soil properties. Rev Bras Cienc Solo. 2021;45:e0210108. https://doi.org/10.36783/18069657rbcs20210108
https://doi.org/10.36783/18069657rbcs202...
).

Biogenic classes were those that was possible to visualize rounded shapes. These were produced in the intestinal tract of soil macrofauna, mainly Oligochaeta (earthworms). Biogenic classes also include samples where it was possible to visualize the presence and activity of roots. Physicogenic class was defined as those that had angular shapes resulting from the interaction between carbon, clay, cations, and soil wetting and drying cycles. After identification, the relative contribution (% by mass) of each aggregate class from each sample area was determined. To determine relative mass contribution, 100 g of aggregate was weighted for each replicate and area (Pereira et al., 2021Pereira MG, Loss A, Batista I, Melo TR, Silva Neto EC, Pinto LASR. Biogenic and physicogenic aggregates: formation pathways, assessment techniques, and influence on soil properties. Rev Bras Cienc Solo. 2021;45:e0210108. https://doi.org/10.36783/18069657rbcs20210108
https://doi.org/10.36783/18069657rbcs202...
).

Aggregates were crushed and passed through a 2.0-mm-mesh sieve (Teixeira et al., 2017Teixeira PC, Donagemma GK, Fontana A, Teixeira WG. Manual de métodos de análise de solo. 3. ed. rev e ampl. Brasília, DF: Embrapa; 2017.) to analyze organic matter fractions. Humic substances (HS) were obtained by extraction and separation by differential solubility of organic matter in basic or acid medium (fulvic and humic acids, respectively FAC and HAC) and the residue (humin, HUMC) (Benites et al., 2003Benites VM, Madari B, Machado PLOA. Extração e fracionamento quantitativo de substâncias húmicas do solo: um procedimento simplificado de baixo custo. Rio de Janeiro: Embrapa Solos; 2003. (Comunicado técnico, 16).). Total organic carbon of biogenic, physicogenic aggregates (TOCBio and TOCPhy), and humic fractions was determined (Yeomans and Bremner 1988Yeomans JC, Bremner JM. A rapid and precise method for routine determination of organic carbon in soil. Commun. Soil Sci Plant Anal. 1988;19:1467-76. https://doi.org/10.1080/00103628809368027
https://doi.org/10.1080/0010362880936802...
).

Physical grain size fractionation of the soil organic matter (SOM) fractions into particulate fractions (related to the soil sand fraction) and mineral-associated fractions (related to clay and silt fractions) was performed by the Cambardella and Elliot (1993)Cambardella CA, Elliott ET. Methods for physical separation and characterization of soil organic matter fractions. Geoderma. 1993;56:449-57. https://doi.org/10.2136/sssaj1992.03615995005600030017x
https://doi.org/10.2136/sssaj1992.036159...
method. Physical densimetric fractionation of SOM in the light-free fraction (FLF) and light intra-aggregate fraction (ILF) (Sohi et al., 2001Sohi SP, Mahieu N, Arah JRM, Powlson DS, Madari B, Gaunt JL. A procedure for isolating soil organic matter fractions suitable for modeling. Soil Sci Soc Am. 2001;65:1121-8. https://doi.org/10.2136/sssaj2001.6541121x
https://doi.org/10.2136/sssaj2001.654112...
; Machado, 2002Machado PLOA. Fracionamento físico do solo por densidade e granulometria para a quantificação de compartimentos da matéria orgânica do solo: um procedimento para a estimativa pormenorizada do seqüestro de carbono pelo solo. Rio de Janeiro: Embrapa Solos; 2002. (Comunicado técnico, 9).) was performed by separating the little altered organic residues from the more humified organic material, through density. We determined the organic carbon of the particulate fraction (POC), free light fraction (FLFC), and intra-aggregate light fraction (ILFC) of the SOM (Yeomans and Bremner, 1988Yeomans JC, Bremner JM. A rapid and precise method for routine determination of organic carbon in soil. Commun. Soil Sci Plant Anal. 1988;19:1467-76. https://doi.org/10.1080/00103628809368027
https://doi.org/10.1080/0010362880936802...
) and the organic carbon of the mineral-associated fraction (MAOC) of the SOM by the difference between TOC and POC.

Statistical analyses

The study was statistically analyzed in a unifactorial scheme in a completely randomized design for the variables related to litter stock, chemical properties, glomalin and aggregate stability. Statistical study was carried out in a 3 × 2 factorial scheme (three areas evaluated × two aggregate formation pathways) in a completely randomized design for the variables related to aggregate formation pathways. All the data was analyzed for homoscedasticity of variance using Levene’s test. Variables that were not considered homogeneous were transformed and tested again.

All the data was then submitted to analysis of variance using the F-test (ANOVA) when the assumption of homogeneity was met (variables transformed or not) and the means were compared using Bonferroni’s parametric t-test. The statistical tests applied were carried out at a 5 % significance level using the software Sisvar, version 5.6 (Ferreira, 2011Ferreira DF. Sisvar: A computer statistical analysis system. Cienc Agrotec. 2011;35:1039-42. https://doi.org/10.1590/S1413-70542011000600001
https://doi.org/10.1590/S1413-7054201100...
).

In addition, multivariate principal component analysis (PCA) and hierarchical grouping (cluster dendrogram) were carried out based on the properties evaluated, to help distinguish between the areas. Multivariate analyses were also carried out at a 5 % significance level using the R Software (R Development Core Team, 2020R Development Core Team. R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2020. Available from: http://www.R-project.org/.
http://www.R-project.org/...
) using the “Ggplot2” package.

RESULTS

Litter stock, soil total organic carbon content, and stock

The highest values of litter stock (Stocklitter) were quantified in the Eucalyptus and Ecotone areas. The highest values of organic carbon content were quantified in the Eucalyptus area, which did not differ from the Forest and Ecotone area. As for the carbon stock, the highest values were observed in the Forest and Eucalyptus areas (Table 2).

Table 2
Stocklitter, total soil organic carbon content, and stock in the 0.00-0.10 m layer (TOCsoil and StockTOCsoil, respectively) in areas under eucalyptus plantation (Euc), forest-eucalyptus ecotone (Eco), and forest fragment (For), Southeastern Brazil

Chemical, biological and physical properties of 8.0–4.0 mm aggregates

Values of pH, Ca2+, Mg2+, Al3+, and H+Al quantified in the aggregates did not differ among areas (Table 3). The highest content of P and Na+ was observed in the Eucalyptus area when compared with the other areas, which did not differ among themselves. The K+ was higher in the Eucalyptus and Forest areas than in the Ecotone area, but it did not differ among themselves.

Table 3
Chemical properties of the aggregates in areas under eucalyptus plantation (Euc), forest-eucalyptus ecotone (Eco), and forest fragment (For) in the 0.00-0.10 m layer, Southeastern Brazil

In the Eucalyptus area, we observed higher values of GRSP-T and MWDDW compared with the other areas. It also presented higher values of TOCAG compared with the Ecotone area. Forest area presented intermediate values of TOCAG, which did not differ from the other areas (Table 4). There were no differences between the areas for GRSP-EE or MWDWW.

Table 4
Total organic carbon of aggregates (TOCAG), soil protein related to total glomalin (GRSP-T) and easily extractable (GRSP-EE), and weighted mean diameter dry (MWDDW) and wet (MWDWW) in areas under eucalyptus plantation (Euc), forest-eucalyptus ecotone (Eco), and forest fragment (For) in the 0–0.10 m layer, Southeastern Brazil

Hierarchical grouping analysis (Figure 2a), integrating the chemical properties (pH, Ca2+, Mg2+, P, Na+, Al3+ and H+Al), TOCAG, GRSP-T, GRSP-EE, MWDDW and MWDWW of the aggregates, separated the areas in two groups. The first group was formed only by the Eucalyptus area, which presented dissimilarity of approximately 60 % compared to the second group, formed by the Forest and Ecotone areas. The dissimilarity between these two areas was lower than that of the Eucalyptus area, around 40 %, which may be associated with the spatial proximity between them, as well as the same position in the landscape.

Figure 2
Hierarchical clustering dendrogram (a) and principal component analysis (b) integrating chemical properties, total organic carbon, glomalin, and stability of aggregates in areas under eucalyptus plantation (Euc), forest-eucalyptus ecotone (Eco), and forest fragment (For) in the 0.00-0.10 m layer, Southeastern Brazil. pH: active acidity; Ca2+: exchangeable calcium; Mg2+: exchangeable magnesium; Al3+: exchangeable acidity; K: exchangeable potassium; Na+: exchangeable sodium; P: available phosphorus; GRSP-T: total glomalin-related soil protein; GRSP-EE: easily extractable glomalin-related soil protein; MWDdw: dry weighted mean diameter; MWDww: wet weighted mean diameter; and TOCAG: Total organic carbon of aggregates.

In the principal components analysis, it was considered the first two principal components (PC1 and PC2), which explained 66.78 % of the total variability of the data (Figure 2b). This analysis indicated an association of the Eucalyptus area with K+, Na+, P, H+Al, TOCAG, GRSP-T, GRSP-EE, and MWDDW, and an association of the Forest and Ecotone areas with Mg2+ and MWDWW, respectively. The properties that contributed the most to separate the areas, that is, that presented significant influence (correlation coefficient >0.70) on the principal component 1, which explained the greatest variability of the results (41.04 %), were GRSP-T (0.91), Na+, (0.88), TOCAG (0.82), MWDDW (0.80), K+ (0.79) and P (0.73).

Relative proportion and organic matter fractions of biogenic and physicogenic aggregates

Regarding the morphological classification of aggregates, the biogenic morphological class predominated in all areas (88, 89, and 93 % in Eucalyptus, Ecotone, and Forest, respectively), compared to physicogenic (7, 11, and 12 %, respectively) (Figure 3a). However, the relative proportions of these two aggregate formation pathways did not differ among the areas, probably owing to the low degree of anthropogenic disturbance in the study areas.

Figure 3
Relative proportion and total organic carbon (TOC) of biogenic (Bio) and physicogenic (Phy) aggregates of biogenic and physicogenic aggregates in areas under eucalyptus plantation (Euc), forest-eucalyptus ecotone (Eco), and forest fragment (For) in the 0.00-0.10 m layer, Southeastern Brazil. Averages followed by the same letters do not differ significantly by the Bonferroni’s t-test at 5 %. (*) Indicates a significant difference between biogenic and physicogenic aggregates by Bonferroni’s t-test at 5 %.

Higher values of TOCBio and TOCPhy (47.70 and 39.81 g kg-1) were quantified in the Eucalyptus area, compared to the Ecotone (32.44 and 24.21 g kg-1) and Forest (27.72 and 24.70 g kg-1) areas (Figure 3b). The results for these properties corroborate the results verified for Stocklitter, TOCsoil and StockTOCsoil (Table 2), TOCAG, GRSP-T and MWDDW (Table 4). The TOCBio values were higher than TOCPhy values in the Eucalyptus and Ecotone areas (Figure 3b). There were no differences between the TOCBio and TOCPhy values in the Forest area.

Humic acid (HAC), fulvic acid (FAC) and humin (HUMC) fractions showed a similar pattern to that observed for TOCBio and TOCPhy (Figure 2b), with higher levels observed in the physicogenic and biogenic aggregates in the Eucalyptus area compared to the Forest and Ecotone areas (Table 5). These results are also similar to those found for the properties Stocklitter, TOCsoil and StockTOCsoil (Table 2), TOCAG, GRSP-T and MWDDW (Table 4). No differences were found between the Forest and Ecotone areas for these fractions (Table 5).

Table 5
Chemical fractionation of organic matter (g kg-1 and %) of biogenic (bio) and physicogenic (phy) aggregates in areas under eucalyptus plantation (Euc), forest-eucalyptus ecotone (Eco), and forest fragment (For) in the 0.00-0.10 m layer, Southeastern Brazil

Higher content of HAC and HUMC was observed in biogenic aggregates than in physicogenic ones only in the Eucalyptus area (Table 5). In relation to the carbon distribution in these fractions, high carbon concentrations in %HUMC were found for both formation pathways in all areas. Results of %HAC and %HUMC were, in general, higher in the Eucalyptus area than in other areas. %HS predominated in relation to non-humified carbon, both in biogenic and physicogenic aggregates, in the three areas. Proportion of %HS in relation to percentage of non-humified carbon (%HNC) in biogenic and physicogenic aggregates was higher in the Eucalyptus area when compared to the Forest and Ecotone areas (Table 5).

For the particle size physical fractions (particulate organic carbon and associated to minerals, POC and MAOC) and densimetric fractions (organic carbon of the light free and light intra-aggregate fractions, FLFC and ILFC), the highest content was also observed in the Eucalyptus area in both aggregates formation pathways (Table 6). Higher carbon content was observed only in the MAOC fraction in biogenic aggregates in the Ecotone area compared to the Forest area (Table 5).

Table 6
Particle size fractionation of organic matter of biogenic (bio) and physicogenic (phy) aggregates in areas under eucalyptus plantation (Euc), forest-eucalyptus ecotone (Eco), and forest fragment (For) in the 0.00-0.10 m layer, Southeastern Brazil

In biogenic aggregates, high content of POC, MAOC, FLFC, ILFC, %POC, %FLFC, and %ILFC was quantified in most areas (Table 5). Results corroborate those verified for TOCBio (Figure 2b), HAC and HUMC attributes (Table 5). Proportions of %MAOC in relation to %POC predominated in the biogenic and physicogenic aggregates in all areas (Table 6).

Hierarchical grouping analysis for organic matter properties in biogenic and physicogenic aggregates separated the areas and the respective aggregate formation pathways into two large groups (Figure 4a). One group was formed by the Eucalyptus area, where we observed dissimilarity around 80 %, compared to the Ecotone and Forest areas, which were associated by a dissimilarity of approximately 25 % (Figure 4a).

Figure 4
Hierarchical clustering dendrogram (a) and principal component analysis (b) integrating the chemical and physical fractions of organic matter of biogenic (bio) and physicogenic (phy) aggregates in areas under eucalyptus plantation (Euc), forest-eucalyptus ecotone (Eco), and forest fragment (For) in the 0.00-0.10 m layer, Southeastern Brazil. TOC: total organic carbon; POC: particulate organic carbon; MAOC: mineral-associated organic carbon; HAC: humic acids carbon; FAC: fulvic acids carbon; HUMC: humin carbon; FLFC: free light fraction carbon; and ILFC: intra-aggregate light carbon-fraction.

The PCA revealed that the organic matter properties of the different aggregate formation pathways contributed expressively to the differentiation between the areas. Principal components 1 and 2 explained 88.43 % of the total variability of the data (Figure 4b). Principal component 1 explained 82.43 % of the variability of the data and presented high positive correlation coefficients (>0.83) with the properties TOC, HAC, FAC, HUMC, POC, MAOC, FLFC, and ILFC. Principal component 2 explained only 6.0 % of the data variability and showed inexpressive correlations with the attributes (< 0.70) (Figure 4b).

DISCUSSION

Litter stock and soil total organic carbon storage

Relative proportion of eucalyptus leaves in the Eucalyptus area was 14 %, almost three times higher than that observed in the Ecotone area (5 %). The slow decomposition of this material due to the efficient internal retranslocation of N and P (Cunha et al., 2019Cunha GM, Gama-Rodrigues AC, Gama-Rodrigues EF, Moreira GR. Nutrient cycling in Corymbia citriodora in the State of Rio de Janeiro, Brazil. Floresta Ambient. 2019;26:e20170204. https://doi.org/10.1590/2179-8087.020417
https://doi.org/10.1590/2179-8087.020417...
) may have contributed to the high Stocklitter values in such areas (Table 2).

The pattern of higher TOCsoil values in the Eucalyptus area compared to the Forest (Table 2) was the opposite of that observed in a study conducted in the municipality of Chapecó (SC), in which higher values of this property were seen in the Mixed Ombrophilous Forest area than in a plantation of Eucalyptus saligna Sm (Denardin et al., 2014Denardin RBN, Mattias JL, Wildner LP, Nesi CN, Sordi A, Kolling DF, Busnello FJ, Cerutti T. Estoque de carbono no solo sob diferentes formações florestais, Chapecó-SC. Cienc Florest. 2014;24:59-69. https://doi.org/10.5902/1980509813323
https://doi.org/10.5902/1980509813323...
). This divergence was probably due to the difference in age of the plantations, which was eight years in that study, and 100 years in the present study.

Besides age, the positioning of the Eucalyptus area at the lowest point of the landscape may also have contributed to the high TOCsoil and StockTOCsoil values, which did not differ significantly from that quantified in the Forest area due to the disfavoring of the decomposition of soil organic matter (SOM) (Table 2). This pattern is based on the rainfall coming from the highest parts, where Forest and Ecotone areas are located, as it tends to accumulate in the lower part of the landscape. This pattern was verified in areas of forest and forest-field edge ecotone in the southern region of the state of Amazonas, where higher TOCsoil values were recorded in points of the landscape located in the depressions than in those in high areas (Vidotto et al., 2007Vidotto E, Pessenda LCR, Ribeiro AS, Freitas HA, Bendassolli JA. Dinâmica do ecótono floresta-campo no sul do estado do Amazonas no Holoceno, através de estudos isotópicos e fitossociológicos. Acta Amazon. 2007;37:385-400. https://doi.org/10.1590/S0044-59672007000300010
https://doi.org/10.1590/S0044-5967200700...
). Therefore, the maintenance of SOM and soil carbon content and stocks can be affected by numerous factors, such as soil type and initial condition, climate, position in the relief, management practices, time to add the vegetation cover, among others (Denardin et al., 2014Denardin RBN, Mattias JL, Wildner LP, Nesi CN, Sordi A, Kolling DF, Busnello FJ, Cerutti T. Estoque de carbono no solo sob diferentes formações florestais, Chapecó-SC. Cienc Florest. 2014;24:59-69. https://doi.org/10.5902/1980509813323
https://doi.org/10.5902/1980509813323...
), which influence the relationship between carbon input and the decomposition/mineralization process of SOM.

It is worth noting that the Eucalyptus area was classified as having a loam texture in the first 0.10 m of depth, with lower clay contents (242 g kg-1) compared to the Ecotono (clay loam) and Forest (silty clay loam) areas, with clay contents of around 399 and 364 g kg-1 (Table 1). This could compromise the accumulation of SOM in the Eucalyptus area. The TOCsoil and StockTOCsoil results show that soil texture was not a limiting factor for the accumulation of SOM in the Eucalyptus area, since the medium-textured area is storing more carbon, especially when compared to the clay-textured Ecotone area (Table 2).

High value of StockTOCsoil in the Forest area may be related to the stability of this ecosystem, reflected by the continuous addition of organic material via litter and subsurface due to the renewal of the root system (Table 2). Changes in this material occur in specific situations (droughts, frosts, and fires, among others), but whose effects, due to the periodicity and/or intensity, normally do not manifest themselves in the levels of carbon stored in the soil (Alves et al., 2008Alves BJR, Urquiaga S, Jantalia CP, Boddey RM. Dinâmica do carbono em solos sob pastagem. In: Santos GA, Silva LS, Canellas LP, Camargo FAO, editors. Fundamentos da matéria orgânica do solo: Ecossistemas tropicais e subtropicais. 2.ed. Porto Alegre: Editora Metrópole; 2008. p. 561-9.; Costa et al., 2008Costa FS, Bayer C, Zanatta JA, Mielniczuk J. Estoque de carbono orgânico no solo emissões de dióxido de carbono influenciadas por sistemas de manejo no sul do Brasil. Rev Bras Cienc Solo. 2008;32:323-32. https://doi.org/10.1590/S0100-06832008000100030
https://doi.org/10.1590/S0100-0683200800...
).

Fertility, glomalin and stability of aggregates

Variation between the areas regarding the composition of the plant community and, consequently, the chemical quality of the litter, probably influenced the difference between the areas with respect to the content of P and K+ in the topsoil (0.00-0.10 m) (Table 3). In northern China, revegetation under agro-pastoral ecotone led to increased TOC levels in both deformed and aggregate samples, mainly owing to changes in macroaggregation (Yao et al., 2019Yao Y, Ge N, Yu S, Wei X, Wang X, Jin J, Liu X, Shao M, Wei Y, Kang L. Response of aggregate associated organic carbon, nitrogen and phosphorous to re-vegetation in agro-pastoral ecotone of northern China. Geoderma, 2019;341:172-80. https://doi.org/10.1016/j.geoderma.2019.01.036
https://doi.org/10.1016/j.geoderma.2019....
). However, this increase was even greater when fabaceous species were used in the revegetation of the areas compared to other species after approximately 20 years.

High values of GRSP-T and MWDDW (Table 4) may be associated with the high value of TOCsoil (Table 2), in the Eucalyptus area. Some authors found a significant positive correlation between glomalin fractions and TOC content in uncultivated and cultivated soils (Nichols and Wright, 2005Nichols KA, Wright SF. Comparison of glomalin and humic acid in eight native US soils. Soil Science. 2005;170:985-97. https://doi.org/10.1097/01.ss.0000198618.06975.3c
https://doi.org/10.1097/01.ss.0000198618...
; Lima et al., 2013Lima FS, Soares ACF, Sousa CS. Ocorrência e atividade de fungos micorrízicos arbusculares em plantios de eucalipto (Eucalyptus sp.) no litoral norte da Bahia, Brasil. Rev Arvore. 2013;37:245-55. https://doi.org/10.1590/S0100-67622013000200006
https://doi.org/10.1590/S0100-6762201300...
), probably owing to the similarity between these properties regarding the dynamics of decomposition (Bedini et al., 2007Bedini S, Avio L, Argese E, Giovannetti M. Effects of long-term land use on arbuscular mycorrhizal fungi and glomalin-related soil protein. Agr Ecosyst Environ. 2007;120:463-6. https://doi.org/10.1016/j.agee.2006.09.010
https://doi.org/10.1016/j.agee.2006.09.0...
). The high stability of aggregates is directly related to the carbon content in the soil (Hickmann et al., 2011Hickmann C, Costa LM, Schaefer CEGR, Fernandes RBA. Morfologia e estabilidade de agregados superficiais de um Argissolo Vermelho-Amarelo sob diferentes manejos de longa duração e Mata Atlântica secundária. Rev Bras Cienc Solo. 2011;35:21918. https://doi.org/10.1590/S0100-06832011000600034
https://doi.org/10.1590/S0100-0683201100...
).

According to Wright et al. (2007)Wright SF, Green VS, Cavigelli MA. Glomalin in aggregate size classes from three different farming systems. Soil Till Res. 2007;94:546-9. https://doi.org/10.1016/j.still.2006.08.003
https://doi.org/10.1016/j.still.2006.08....
, GRSP is related to increased aggregate stability and can provide a quantitative measure of specific SOM components. Pinto et al. (2022)Pinto LASR, Silva CF, Melo TR, Rosset JS, Pereira MG. Stability, labile organic carbon, and glomalin of biogenic aggregates in sandy soils under management systems in the subtropical region of Brazil. Rev Bras Cienc Solo. 2022;46:e0220074. https://doi.org/10.36783/18069657rbcs20220074
https://doi.org/10.36783/18069657rbcs202...
found relationships between oxidizable carbon, GRSP-EE, GRSP-T, and MWD in areas under different management systems, for example. According to the authors, these results show that the associations between binding agents and the stability of aggregates are more dependent on carbon concentrations and less disturbance of the arable layer, and are more related to macroaggregates than microaggregates. The GRSP levels can vary from 2.0 to 15.0 mg g-1 in arable soils, pastures and natural ecosystems (Wright and Upadhyaya 1996Wright SF, Upadhyaya AA. Extraction of an abundant and unusual protein from soil and comparison with hyphal protein of arbuscular mycorrhizal fungi. Soil Sci. 1996;161:575-86. https://doi.org/10.1097/00010694-199609000-00003
https://doi.org/10.1097/00010694-1996090...
; Wright et al., 2000Wright SF, Rillig MC, Nichols KA. Glomalin: A soil protein important in carbon sequestration. Proc Am Chem Soc. 2000;220:721-5.). The levels quantified in this study are within the range indicated by the authors.

It is worth noting that the MWD values in both methods of assessing the state of aggregation (wet and dry) were above 4.0 in all three areas (Table 4). Studies have observed that MWD values below 2.0 mm indicate soils in unfavorable physical conditions with regard to aeration; water infiltration and redistribution; and root system establishment (Briedis et al., 2012Briedis C, Sá JCM, Caires EF, Navarro JF, Inagaki TM, Boer A, Quadros Neto C, Ferreira AO, Canalli LB, Santos JB. Soil organic matter pools and carbon-protection mechanisms in aggregates classes influenced by surface liming in a no till system. Geoderma. 2012;170:80-8. https://doi.org/10.1016/j.geoderma.2011.10.011
https://doi.org/10.1016/j.geoderma.2011....
; Tivet et al., 2013Tivet F, Sá JCM, Lal R, Briedis C, Borszowskei PR, Santos JB, Farias A, Eurich G, Hartman DC, Junior MN. Aggregate C depletion by plowing and its restoration by diverse biomass-C inputs under no-till in sub-tropical and tropical regions of Brazil. Soil Till Res. 2013;126:203-18. https://doi.org/10.1016/j.still.2012.09.004
https://doi.org/10.1016/j.still.2012.09....
). Multivariate analysis (Figure 2) was more efficient in separating the areas evaluated based on the analysis of chemical properties, glomalin and stability of 8.0–4.0 mm aggregates. The PCA (Figure 2a) showed that only the Mg2+ and MWDWW properties were not influenced by the soil conditions related to the Eucalyptus area.

Aggregate formation pathways and associated organic matter

Relative proportions of these two aggregate formation pathways did not differ between the areas, probably due to the low degree of anthropogenic disturbance in the study areas (Figure 3a). As for relative proportion and SOM fractions of biogenic and physicogenic aggregates the pattern observed may indicate the similarity between the areas regarding the availability of favorable conditions for the activity of soil fauna, which is the main precursor of biogenic aggregates (Jouquet et al., 2006Jouquet P, Dauber J, Lagerlöf J, Lavelle P, Lepage M. Soil invertebrates as ecosystem engineers: Intended and accidental effects on soil and feedback loops. Appl Soil Ecol. 2006;32:153-64. https://doi.org/10.1016/j.apsoil.2005.07.004
https://doi.org/10.1016/j.apsoil.2005.07...
; Fernandes et al., 2017Fernandes JCF, Pereira MG, Silva Neto ECA, Correa Neto TA. Characterization of biogenic, intermediate and physicogenic soil aggregates of areas in the Brazilian Atlantic Forest. Rev Caatinga. 2017;30:59-67. https://doi.org/10.1590/1983-21252017v30n107rc
https://doi.org/10.1590/1983-21252017v30...
), such as microclimate and soil chemical and physical properties.

Presence of trees and litter stock favor the activity of macrofauna, allowing them to act on the soil forming biogenic structures by homogenizing the mineral and organic fractions (Suárez et al., 2019Suárez LR, Audor LCU, Salazar JCS. Formation of macroaggregates and organic carbon in cocoa agroforestry systems. Floresta Ambient. 2019;26:e20180312. https://doi.org/10.1590/2179-8087.031218
https://doi.org/10.1590/2179-8087.031218...
). In general, differences are observed between areas regarding this property when comparing regions of Atlantic Forest under different regeneration stages, as verified in southeastern Brazil (Silva Neto et al., 2016Silva Neto EC, Pereira MG, Fernandes JCF, Corrêa Neto T A. Aggregate formation and soil organic matter under different vegetation types in Atlantic Forest from Southeastern Brazil. Semina. 2016;37:3927-40. https://doi.org/10.5433/1679-0359.2016v37n6p3927
https://doi.org/10.5433/1679-0359.2016v3...
; Fernandes et al., 2017Fernandes JCF, Pereira MG, Silva Neto ECA, Correa Neto TA. Characterization of biogenic, intermediate and physicogenic soil aggregates of areas in the Brazilian Atlantic Forest. Rev Caatinga. 2017;30:59-67. https://doi.org/10.1590/1983-21252017v30n107rc
https://doi.org/10.1590/1983-21252017v30...
). In the Colombian Amazon, Suárez et al. (2019)Suárez LR, Audor LCU, Salazar JCS. Formation of macroaggregates and organic carbon in cocoa agroforestry systems. Floresta Ambient. 2019;26:e20180312. https://doi.org/10.1590/2179-8087.031218
https://doi.org/10.1590/2179-8087.031218...
classifying soil macroaggregates under forest area into biogenic aggregates from fauna (coprolites) and flora (root), physicogenic and non-macroaggregated fraction, quantified proportions of 16.0, 12.5, 18.7, and 52.3 %, respectively.

In southeastern Brazil, Schultz et al. (2019)Schultz N, Pinto LASR, Lima SS, Ziviani MM, Assunção AS, Pereira MG. Agregação do solo e atributos químicos em áreas com diferentes coberturas vegetais. In: Tulio L, editor. Características do solo e sua interação com as plantas 2. Ponta Grossa: Editora Atena; 2019. vol. 2. p. 1-12. https://doi.org/10.22533/at.ed.1781917101
https://doi.org/10.22533/at.ed.178191710...
, evaluating the influence of tree vegetation and grasses on aggregate formation pathways in Argissolo Vermelho-Amarelo (Udult), verified a predominance of biogenic aggregates (70.5 and 63.0 %) compared to physicogenic (29.5 and 37.0 %) in an area of tree vegetation. In Paraná, Southern Brazil, under Latossolo Vermelho Eutroférrico (Rhodic Ferralsol), Ferreira et al. (2020)Ferreira CR, Silva Neto EC, Pereira MG, Guedes JN, Rosset JS, Anjos LHC. Dynamics of soil aggregation and organic carbon fractions over 23 years of no-till management. Soil Till Res. 2020;198:104533. https://doi.org/10.1016/j.still.2019.104533
https://doi.org/10.1016/j.still.2019.104...
observed that the proportion of biogenic aggregates was higher (51.2 and 53.8 %) than that of intermediate (27.5 and 25.1 %) and physicogenic (21.3 and 21.1 %) aggregates in a native Atlantic Forest fragment in two sampling seasons. Presence of biogenic aggregates, invertebrates, and roots demonstrates high biological activity, which probably indicates a high quality in soil processes and optimal biological regulation in the functioning of the edaphic system (Velasquez and Lavelle, 2019Velasquez E, Lavelle P. Soil macrofauna as an indicator for evaluating soil-based ecosystem services in agricultural landscapes. Acta Oecol. 2019;100:103446. https://doi.org/10.1016/j.actao.2019.103446
https://doi.org/10.1016/j.actao.2019.103...
).

The pattern of TOC results between the aggregate formation pathways (Figure 3b) resembles the pattern seen in other studies (Pulleman et al., 2005Pulleman MM, Six J, Marinissen JCY, Jongmans AG. Earthworms and management affect organic matter incorporation and microaggregate formation in agricultural soils. Appl Soil Ecol. 2005;29:1-15. https://doi.org/10.1016/j.apsoil.2004.10.003
https://doi.org/10.1016/j.apsoil.2004.10...
; Silva Neto et al., 2016; Fernandes et al., 2017Fernandes JCF, Pereira MG, Silva Neto ECA, Correa Neto TA. Characterization of biogenic, intermediate and physicogenic soil aggregates of areas in the Brazilian Atlantic Forest. Rev Caatinga. 2017;30:59-67. https://doi.org/10.1590/1983-21252017v30n107rc
https://doi.org/10.1590/1983-21252017v30...
; Schultz et al., 2019Schultz N, Pinto LASR, Lima SS, Ziviani MM, Assunção AS, Pereira MG. Agregação do solo e atributos químicos em áreas com diferentes coberturas vegetais. In: Tulio L, editor. Características do solo e sua interação com as plantas 2. Ponta Grossa: Editora Atena; 2019. vol. 2. p. 1-12. https://doi.org/10.22533/at.ed.1781917101
https://doi.org/10.22533/at.ed.178191710...
; Suárez et al., 2019Suárez LR, Audor LCU, Salazar JCS. Formation of macroaggregates and organic carbon in cocoa agroforestry systems. Floresta Ambient. 2019;26:e20180312. https://doi.org/10.1590/2179-8087.031218
https://doi.org/10.1590/2179-8087.031218...
). According to Pinto et al. (2022)Pinto LASR, Silva CF, Melo TR, Rosset JS, Pereira MG. Stability, labile organic carbon, and glomalin of biogenic aggregates in sandy soils under management systems in the subtropical region of Brazil. Rev Bras Cienc Solo. 2022;46:e0220074. https://doi.org/10.36783/18069657rbcs20220074
https://doi.org/10.36783/18069657rbcs202...
, the results verified in this study (Figure 3b) reinforce the hypothesis that biogenic aggregates lead to improved soil quality, especially with regard to their greater capacity to preserve and accumulate the more soluble fractions of SOM. In the Forest area, higher TOC content was recorded in biogenic aggregates compared to intermediate and physicogenic aggregates (Ferreira et al., 2020Ferreira CR, Silva Neto EC, Pereira MG, Guedes JN, Rosset JS, Anjos LHC. Dynamics of soil aggregation and organic carbon fractions over 23 years of no-till management. Soil Till Res. 2020;198:104533. https://doi.org/10.1016/j.still.2019.104533
https://doi.org/10.1016/j.still.2019.104...
). Higher TOC levels were determined in biogenic aggregates compared to the physicogenic pathway in forest fragments under different relief conditions in southeastern Brazil (Pinto et al., 2021Pinto LASR, Freo VA, Pereira MG, Medeiros AS, Silva CF, Santos OAQ, Souza RS. Agregação sob diferentes pedoformas em floresta estacional semidecidual, no Sudeste do Brasil. In: Santos TR, editor. Engenharia Agronômica: Ambientes Agrícolas e seus Campos de Atuação 3. ed. Ponta Grossa: Atena Editora; 2021. p. 119-33. https://doi.org/10.22533/at.ed.41121030512
https://doi.org/10.22533/at.ed.411210305...
).

It is also noteworthy in this study that, in the biogenic aggregates of the Eucalyptus area, higher levels of organic carbon were quantified (numerically) compared to that of the sampled soil and the 8.0-4.0 mm aggregates (47.70, 44.67 and 39.00 g kg-1, TOCBio, TOCsoil, and TOCAG, respectively) (Figure 3b, Tables 2 and 3). In areas with the absence or low intensity of anthropic actions, it is assumed high activity of biological agents (macrofauna and flora), responsible for the addition and incorporation of carbon in aggregates of biogenic origin (Pinto et al., 2022Pinto LASR, Silva CF, Melo TR, Rosset JS, Pereira MG. Stability, labile organic carbon, and glomalin of biogenic aggregates in sandy soils under management systems in the subtropical region of Brazil. Rev Bras Cienc Solo. 2022;46:e0220074. https://doi.org/10.36783/18069657rbcs20220074
https://doi.org/10.36783/18069657rbcs202...
). Thus, it can be inferred that the enrichment of organic carbon in biogenic aggregates was more evident in comparison with the deformed soil samples, and that these aggregates, besides indicating greater biological activity, also promote the accumulation of organic carbon in the soil (Ferreira et al., 2020Ferreira CR, Silva Neto EC, Pereira MG, Guedes JN, Rosset JS, Anjos LHC. Dynamics of soil aggregation and organic carbon fractions over 23 years of no-till management. Soil Till Res. 2020;198:104533. https://doi.org/10.1016/j.still.2019.104533
https://doi.org/10.1016/j.still.2019.104...
; Pinto et al., 2021Pinto LASR, Freo VA, Pereira MG, Medeiros AS, Silva CF, Santos OAQ, Souza RS. Agregação sob diferentes pedoformas em floresta estacional semidecidual, no Sudeste do Brasil. In: Santos TR, editor. Engenharia Agronômica: Ambientes Agrícolas e seus Campos de Atuação 3. ed. Ponta Grossa: Atena Editora; 2021. p. 119-33. https://doi.org/10.22533/at.ed.41121030512
https://doi.org/10.22533/at.ed.411210305...
).

For organic matter fractions, higher levels of HAC and HUMC in biogenic aggregates (Table 5) were also verified by other authors, who suggest that the biogenic pathway can be adopted as a potential indicator in the evaluation of soil quality, owing to its greater sensitivity to different soil and environmental conditions (Silva Neto et al., 2010Silva Neto LF, Silva IF, Inda AV, Nascimento PC, Bortolo L. Atributos físicos e químicos de agregados pedogênicos e de coprólitos de minhocas em diferentes classes de solos da Paraíba. Cienc Agrotec. 2010;34:1365-71. https://doi.org/10.1590/S1413-70542010000600002
https://doi.org/10.1590/S1413-7054201000...
; Loss et al., 2014Loss A, Pereira MG, Costa EL, Beutler SJ. Soil fertility, physical and chemical organic matter fractions, natural 13C and 15N abundance in biogenic and physicogenic aggregates in areas under different land use systems. Soil Res. 2014;52:685-97. https://doi.org/10.1071/SR14045
https://doi.org/10.1071/SR14045...
; Fernandes et al., 2017Fernandes JCF, Pereira MG, Silva Neto ECA, Correa Neto TA. Characterization of biogenic, intermediate and physicogenic soil aggregates of areas in the Brazilian Atlantic Forest. Rev Caatinga. 2017;30:59-67. https://doi.org/10.1590/1983-21252017v30n107rc
https://doi.org/10.1590/1983-21252017v30...
). Higher levels of FAC, HAC, HUMC, and %HS in biogenic aggregates compared to those in the physicogenic pathway (Table 5) indicate that the former aggregates have the ability to protect and stabilize humic substances, also favoring the maintenance and accumulation of carbon in these fractions (Pinto et al., 2021Pinto LASR, Freo VA, Pereira MG, Medeiros AS, Silva CF, Santos OAQ, Souza RS. Agregação sob diferentes pedoformas em floresta estacional semidecidual, no Sudeste do Brasil. In: Santos TR, editor. Engenharia Agronômica: Ambientes Agrícolas e seus Campos de Atuação 3. ed. Ponta Grossa: Atena Editora; 2021. p. 119-33. https://doi.org/10.22533/at.ed.41121030512
https://doi.org/10.22533/at.ed.411210305...
; Rossi et al., 2023Rossi CQ, Pinto LA, Moura OV, Loss A, Pereira MG. Soil organic matter in biogenic, intermediate and physicogenic aggregates under agroecological management. Rev Caatinga. 2023;36:167-76. https://doi.org/10.1590/1983-21252023v36n118rc
https://doi.org/10.1590/1983-21252023v36...
).This pattern was also observed in other studies (Pulleman et al., 2005Pulleman MM, Six J, Marinissen JCY, Jongmans AG. Earthworms and management affect organic matter incorporation and microaggregate formation in agricultural soils. Appl Soil Ecol. 2005;29:1-15. https://doi.org/10.1016/j.apsoil.2004.10.003
https://doi.org/10.1016/j.apsoil.2004.10...
; Loss et al., 2014Loss A, Pereira MG, Costa EL, Beutler SJ. Soil fertility, physical and chemical organic matter fractions, natural 13C and 15N abundance in biogenic and physicogenic aggregates in areas under different land use systems. Soil Res. 2014;52:685-97. https://doi.org/10.1071/SR14045
https://doi.org/10.1071/SR14045...
; Schultz et al., 2019Schultz N, Pinto LASR, Lima SS, Ziviani MM, Assunção AS, Pereira MG. Agregação do solo e atributos químicos em áreas com diferentes coberturas vegetais. In: Tulio L, editor. Características do solo e sua interação com as plantas 2. Ponta Grossa: Editora Atena; 2019. vol. 2. p. 1-12. https://doi.org/10.22533/at.ed.1781917101
https://doi.org/10.22533/at.ed.178191710...
).

In the Atlantic Forest biome, Rossi et al. (2023)Rossi CQ, Pinto LA, Moura OV, Loss A, Pereira MG. Soil organic matter in biogenic, intermediate and physicogenic aggregates under agroecological management. Rev Caatinga. 2023;36:167-76. https://doi.org/10.1590/1983-21252023v36n118rc
https://doi.org/10.1590/1983-21252023v36...
found an increase in the organic carbon content of the humic and oxidizable fractions of SOM in biogenic aggregates, especially those formed under coffee systems grown in full sun, coffee shaded by gliricidia and agroforestry systems. Studying fragments of the Atlantic Forest at different stages of regeneration, Fernandes et al. (2017)Fernandes JCF, Pereira MG, Silva Neto ECA, Correa Neto TA. Characterization of biogenic, intermediate and physicogenic soil aggregates of areas in the Brazilian Atlantic Forest. Rev Caatinga. 2017;30:59-67. https://doi.org/10.1590/1983-21252017v30n107rc
https://doi.org/10.1590/1983-21252017v30...
quantified higher levels of HUMC in biogenic aggregates. For the authors, these results are related to the agents responsible for the formation of these aggregates, especially earthworms (edaphic macrofauna), since they have a direct action on biogeochemical cycling in the soil (Jouquet et al., 2006Jouquet P, Dauber J, Lagerlöf J, Lavelle P, Lepage M. Soil invertebrates as ecosystem engineers: Intended and accidental effects on soil and feedback loops. Appl Soil Ecol. 2006;32:153-64. https://doi.org/10.1016/j.apsoil.2005.07.004
https://doi.org/10.1016/j.apsoil.2005.07...
), positively affecting the ecology of the humification process (Fernandes et al., 2017Fernandes JCF, Pereira MG, Silva Neto ECA, Correa Neto TA. Characterization of biogenic, intermediate and physicogenic soil aggregates of areas in the Brazilian Atlantic Forest. Rev Caatinga. 2017;30:59-67. https://doi.org/10.1590/1983-21252017v30n107rc
https://doi.org/10.1590/1983-21252017v30...
; Rossi et al., 2023Rossi CQ, Pinto LA, Moura OV, Loss A, Pereira MG. Soil organic matter in biogenic, intermediate and physicogenic aggregates under agroecological management. Rev Caatinga. 2023;36:167-76. https://doi.org/10.1590/1983-21252023v36n118rc
https://doi.org/10.1590/1983-21252023v36...
).

Results of the physical fractions of SOM (POC, FLFC, and ILFC) in biogenic aggregates indicate the predominance of organic material of high lability (great availability), whose incorporation dynamics, maintenance, and accumulation are benefited by edaphic biological activity (soil fauna and root system) (Loss et al., 2014Loss A, Pereira MG, Costa EL, Beutler SJ. Soil fertility, physical and chemical organic matter fractions, natural 13C and 15N abundance in biogenic and physicogenic aggregates in areas under different land use systems. Soil Res. 2014;52:685-97. https://doi.org/10.1071/SR14045
https://doi.org/10.1071/SR14045...
; Pinto et al., 2022Pinto LASR, Silva CF, Melo TR, Rosset JS, Pereira MG. Stability, labile organic carbon, and glomalin of biogenic aggregates in sandy soils under management systems in the subtropical region of Brazil. Rev Bras Cienc Solo. 2022;46:e0220074. https://doi.org/10.36783/18069657rbcs20220074
https://doi.org/10.36783/18069657rbcs202...
). Such aggregates provide a favorable environment for the physical protection of these fractions after encapsulation.

Results for the properties of Stocklitter, TOCsoil, StockTOCsoil (Table 2), TOCAG, GRSP-T, MWDDW (Table 4), TOCBio, TOCPhy (Figure 3 b), HAC, FAC, HUMC (Table 5), POC, MAOC, FLFC, and ILFC (Table 6) in the Eucalyptus area may be related to the characteristics of the area discussed above. As for multivariate analysis, in this study, the main axis separated the forest and ecotone areas, located in the upper and lower left quadrants, from the eucalyptus area, located in the upper and lower right quadrants, whose variables were more associated with the latter area (Figure 4b). This has corroborated the results of the statistical tests applied.

Evaluating the PCA results, Ferreira et al. (2020)Ferreira CR, Silva Neto EC, Pereira MG, Guedes JN, Rosset JS, Anjos LHC. Dynamics of soil aggregation and organic carbon fractions over 23 years of no-till management. Soil Till Res. 2020;198:104533. https://doi.org/10.1016/j.still.2019.104533
https://doi.org/10.1016/j.still.2019.104...
found that the analysis showed a clear distinction between the environments evaluated, in which the attributes associated with SOM in the native forest area showed positive values and high correlation with PC1, unlike the managed areas, in which negative values were observed. Pinto et al. (2021)Pinto LASR, Freo VA, Pereira MG, Medeiros AS, Silva CF, Santos OAQ, Souza RS. Agregação sob diferentes pedoformas em floresta estacional semidecidual, no Sudeste do Brasil. In: Santos TR, editor. Engenharia Agronômica: Ambientes Agrícolas e seus Campos de Atuação 3. ed. Ponta Grossa: Atena Editora; 2021. p. 119-33. https://doi.org/10.22533/at.ed.41121030512
https://doi.org/10.22533/at.ed.411210305...
also verified in their study a clear separation between the evaluated areas and the pattern observed in the PCA in association with the statistical tests applied, evidencing the favoring of biogenic aggregation compared to the different fractions of SOM.

The variables TOC, HAC, FAC, HUMC, POC, MAOC, FLFC and ILFC were those that most contributed to the discrimination of areas in the study of aggregates formation pathways and SOM-associated (Figure 4b). This has reinforced the hypothesis of a possible direct relationship between these indicators in the Eucalyptus area, reflecting the edaphic conditions of the area, which favor the mechanisms of stabilization and accumulation of SOM, especially in biogenic aggregates.

CONCLUSIONS

Litter stock was higher in the Eucalyptus and Ecotone areas than in the Forest area, probably owing to the slow decomposition of the litter deposited by the eucalyptus.

Characterization of the chemical, biological, and physical properties of aggregates, as well as the compartmentalization of SOM-associated with aggregates of different origins (biogenic and physicogenic), allowed to discriminate the Forest and Ecotone areas from the Eucalyptus area.

In biogenic aggregates, higher levels of total organic carbon and its respective chemical and physical fractions were found than in the physicogenic ones, which highlighted the importance of studying the origin of aggregates in the evaluation of soil quality in different forest ecosystems.

Dynamics of edaphic properties in the Ecotone area is similar to the forest fragment, compared to the eucalyptus plantation. However, in general, all different vegetation covers contribute to the maintenance of soil quality in the Nova Baden State Park area.

ACKNOWLEDGMENTS

Authors acknowledge the support from CAPES, CNPq, FAPERJ, PPGCAF/UFRRJ and PPGA-CS/UFRRJ. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001 and Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ). To the State Forestry Institute and to Nova Baden State Park

  • How to cite: Fonseca Júnior AM, Pinto LASR, Silva CF, Ferreira R, Morais IS, Camara R, Delgado RC, Pereira MG. Edaphic properties in a eucalyptus-forest ecotone in the Nova Baden State Park, Southeastern Brazil. Rev Bras Cienc Solo. 2023;47:e0230074 https://doi.org/10.36783/18069657rbcs20230074

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Edited by

Editors: José Miguel Reichert https://orcid.org/0000-0001-9943-2898 and Milton César Costa Campos https://orcid.org/0000-0002-8183-7069.

Publication Dates

  • Publication in this collection
    22 Dec 2023
  • Date of issue
    2023

History

  • Received
    27 June 2023
  • Accepted
    29 Sept 2023
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E-mail: sbcs@sbcs.org.br