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Despite the importance of earthworms for soil formation, more is needed to know about how Pre-Columbian modifications to soils and the landscape. Gaining a deeper understanding is essential for comprehending the historical drivers of earthworm communities and the development of effective conservation strategies in the Amazon rainforest. Human disturbance can significantly impact earthworm diversity, especially in rainforest soils, and in the particular case of the Amazonian rainforest, both recent and ancient anthropic practices may be important. Amazonian Dark Earths (ADEs) are fertile soils found throughout the Amazon Basin, created by sedentary habits and intensification patterns of pre-Colombian societies primarily developed in the second part of the Holocene period. We have sampled earthworm communities in three Brazilian Amazonian (ADEs) and adjacent reference soils (REF) under old and young forests and monocultures. To better assess taxonomic richness, we used morphology and the barcode region of the COI gene to identify juveniles and cocoons and delimit Molecular Operational Taxonomic Units (MOTUs). Here we suggest using Integrated Operational Taxonomical units (IOTUs) which combine both morphological and molecular data and provide a more comprehensive assessment of diversity, while MOTUs only rely on molecular data. A total of 970 individuals were collected, resulting in 51 taxonomic units (IOTUs, MOTUs, and morphospecies combined). From this total, 24 taxonomic units were unique to REF soils, 17 to ADEs, and ten were shared between both soils. The highest richness was found in old forest sites for ADEs (12 taxonomic units) and REFs (21 taxonomic units). The beta-diversity calculations reveal a high species turnover between ADEs and REF soils, providing evidence that ADEs and REFs possess distinct soil biota. Furthermore, results suggest that ADE sites, formed by Pre-Columbian human activities, conserve a high number of native species in the landscape and maintain a high abundance, despite their long-term nature.

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Amazonia has as least two major centers of ancient human social complexity, but the full geographic extents of these centers remain uncertain. Across the southern rim of Amazonia, over 1,000 earthwork sites comprised of fortified settlements, mound villages, and ditched enclosures with geometric designs known as geoglyphs have been discovered. Qualitatively distinct and densely located along the lower stretches of major river systems and the Atlantic coast are Amazonian Dark Earth sites (ADEs) with deep anthropogenic soils enriched by long-term human habitation. Models predicting the geographic extents of earthworks and ADEs can assist in their discovery and preservation and help answer questions about the full degree of indigenous landscape modifications across Amazonia. We classify earthworks versus ADEs versus other non-earthwork/non-ADE archaeological sites with multi-class machine learning algorithms using soils, climate, and distances to rivers of different types and sizes as geospatial predictors. Model testing is done with spatial cross-validation, and the best model at the optimal spatial scale of 1 km has an Area Under the Curve of 0.91. Our predictive model has led to the discovery of 13 new geoglyphs, and it pinpoints specific areas with high probabilities of undiscovered archaeological sites that are currently hidden by rainforests. The limited, albeit impressive, predicted extents of earthworks and ADEs means that other non-ADE/non-earthwork sites are expected to predominate most of Western and Northern Amazonia.

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Amazonian rainforests, once thought to be pristine wilderness, are increasingly known to have been widely inhabited, modified, and managed prior to European arrival, by human populations with diverse cultural backgrounds. Amazonian Dark Earths (ADEs) are fertile soils found throughout the Amazon Basin, created by pre-Columbian societies with sedentary habits. Much is known about the chemistry of these soils, yet their zoology has been neglected. Hence, we characterized soil fertility, macroinvertebrate communities, and their activity at nine archeological sites in three Amazonian regions in ADEs and adjacent reference soils under native forest (young and old) and agricultural systems. We found 673 morphospecies and, despite similar richness in ADEs (385 spp.) and reference soils (399 spp.), we identified a tenacious pre-Columbian footprint, with 49% of morphospecies found exclusively in ADEs. Termite and total macroinvertebrate abundance were higher in reference soils, while soil fertility and macroinvertebrate activity were higher in the ADEs, and associated with larger earthworm quantities and biomass. We show that ADE habitats have a unique pool of species, but that modern land use of ADEs decreases their populations, diversity, and contributions to soil functioning. These findings support the idea that humans created and sustained high-fertility ecosystems that persist today, altering biodiversity patterns in Amazonia.

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Abstract Although manioc is well adapted to nutrient-poor Oxisols of Amazonia, ethnobotanical observations show that bitter manioc is also frequently cultivated in the highly fertile soils of the floodplains and Amazonian dark earths (ADE) along the middle Madeira River. Because different sets of varieties are grown in each soil type, and there are agronomic similarities between ADE and floodplain varieties, it was hypothesized that varieties grown in ADE and floodplain were more closely related to each other than either is to varieties grown in Oxisols. We tested this hypothesis evaluating the intra-varietal genetic diversity and the genetic relationships among manioc varieties commonly cultivated in Oxisols, ADE and floodplain soils. Genetic results did not agree with ethnobotanical expectation, since the relationships between varieties were variable and most individuals of varieties with the same vernacular name, but grown in ADE and floodplain, were distinct. Although the same vernacular name could not always be associated with genetic similarities, there is still a great amount of variation among the varieties. Many ecological and genetic processes may explain the high genetic diversity and differentiation found for bitter manioc varieties, but all contribute to the maintenance and amplification of genetic diversity within the manioc in Central Amazonia.

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Studies of heavy metals adsorption in soil play a key role in predicting environmental susceptibility to contamination by toxic elements. The objective of this study was to evaluate cadmium (Cd) and copper (Cu) adsorption in surface and subsurface soil. Samples of six soils: Xanthic Hapludox (XH1 and XH2), Typic Hapludox (TH), Typic Rhodudalf (TR), Typic Fluvaquent (TF), and Amazonian dark earths (ADE) from Eastern Amazonian, Brazil. The soils were selected for chemical, physical and mineralogical characterization and to determine the adsorption by Langmuir and Freundlich isotherms. All soils characterized as kaolinitic, and among them, XH1 and XH2 showed the lowest fertility. The Langmuir and Freundlich isotherms revealed a higher Cu (H curve) than Cd (L curve) adsorption. Parameters of Langmuir and Freundlich isotherms indicate that soils TR, TF and ADE has the greatest capacity and affinity for metal adsorption. Correlation between the curve adsorption parameters and the soil attributes indicates that the pH, CEC, OM and MnO variables had the best influence on metal retention. The Langmuir and Freundlich isotherms satisfactorily described Cu and Cd soil adsorption, where TR, TF and ADE has a lower vulnerability to metal input to the environment. Besides the pH, CEC and OM the MnO had a significant effect on Cu and Cd adsorption in Amazon soils.

Estudos de adsorção de metais pesados no solo desempenham um papel chave em prever a susceptibilidade à contaminação do ambiente por elementos tóxicos. O objetivo foi avaliar a adsorção de cádmio (Cd) e cobre (Cu) na superfície e subsuperfície de seis solos Amazônicos: Latossolo Amarelo (XH1 e XH2), Latossolo Vermelho (TH), Nitossolo Vermelho (TR), Gleissolo Háplico (TF) e Latossolo Amarelo Terra Preta de Índio (ADE) da Amazônia Oriental. Os solos foram selecionados para caracterização química, física, mineralógica e determinação da capacidade máxima de adsorção pelas isotermas de Langmuir e Freundlich. Todos os solos foram caracterizados como cauliníticos, e entre eles, XH1 e XH2 apresentaram menor fertilidade. As isotermas de Langmuir e Freundlich revelaram adsorção superior de Cu (curva H) em relação ao Cd (L curva). Os parâmetros de Langmuir e Freundlich indicam que os solos TR, TF e ADE tem a maior capacidade e afinidade para adsorção de metais. A correlação entre os parâmetros da curva de adsorção e os atributos do solo indica que o PH, capacidade de troca de cátion (CTC), matéria orgânica (MO) e óxido de manganês (MnO) tiveram influência sobre a retenção dos metais. As isotermas de Langmuir e Freundlich descreveram satisfatoriamente a adsorção de Cu e Cd no solo, onde TR, TF e ADE tem uma menor vulnerabilidade à entrada de metais para o meio ambiente. Além do pH, CTC e MO, o MnO teve um efeito significativo na adsorção de Cu e Cd em solos amazônicos.

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Studies of heavy metals adsorption in soil play a key role in predicting environmental susceptibility to contamination by toxic elements. The objective of this study was to evaluate cadmium (Cd) and copper (Cu) adsorption in surface and subsurface soil. Samples of six soils: Xanthic Hapludox (XH1 and XH2), Typic Hapludox (TH), Typic Rhodudalf (TR), Typic Fluvaquent (TF), and Amazonian dark earths (ADE) from Eastern Amazonian, Brazil. The soils were selected for chemical, physical and mineralogical characterization and to determine the adsorption by Langmuir and Freundlich isotherms. All soils characterized as kaolinitic, and among them, XH1 and XH2 showed the lowest fertility. The Langmuir and Freundlich isotherms revealed a higher Cu (H curve) than Cd (L curve) adsorption. Parameters of Langmuir and Freundlich isotherms indicate that soils TR, TF and ADE has the greatest capacity and affinity for metal adsorption. Correlation between the curve adsorption parameters and the soil attributes indicates that the pH, CEC, OM and MnO variables had the best influence on metal retention. The Langmuir and Freundlich isotherms satisfactorily described Cu and Cd soil adsorption, where TR, TF and ADE has a lower vulnerability to metal input to the environment. Besides the pH, CEC and OM the MnO had a significant effect on Cu and Cd adsorption in Amazon soils.(AU)

Estudos de adsorção de metais pesados no solo desempenham um papel chave em prever a susceptibilidade à contaminação do ambiente por elementos tóxicos. O objetivo foi avaliar a adsorção de cádmio (Cd) e cobre (Cu) na superfície e subsuperfície de seis solos Amazônicos: Latossolo Amarelo (XH1 e XH2), Latossolo Vermelho (TH), Nitossolo Vermelho (TR), Gleissolo Háplico (TF) e Latossolo Amarelo Terra Preta de Índio (ADE) da Amazônia Oriental. Os solos foram selecionados para caracterização química, física, mineralógica e determinação da capacidade máxima de adsorção pelas isotermas de Langmuir e Freundlich. Todos os solos foram caracterizados como cauliníticos, e entre eles, XH1 e XH2 apresentaram menor fertilidade. As isotermas de Langmuir e Freundlich revelaram adsorção superior de Cu (curva H) em relação ao Cd (L curva). Os parâmetros de Langmuir e Freundlich indicam que os solos TR, TF e ADE tem a maior capacidade e afinidade para adsorção de metais. A correlação entre os parâmetros da curva de adsorção e os atributos do solo indica que o PH, capacidade de troca de cátion (CTC), matéria orgânica (MO) e óxido de manganês (MnO) tiveram influência sobre a retenção dos metais. As isotermas de Langmuir e Freundlich descreveram satisfatoriamente a adsorção de Cu e Cd no solo, onde TR, TF e ADE tem uma menor vulnerabilidade à entrada de metais para o meio ambiente. Além do pH, CTC e MO, o MnO teve um efeito significativo na adsorção de Cu e Cd em solos amazônicos.(AU)

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Outsiders often oversimplify Amazon soil use by assuming that abundantly available natural soils are poorly suited to agriculture and that sporadic anthropogenic soils are agriculturally productive. Local perceptions about the potentials and limitations of soils probably differ, but information on these perceptions is scarce. We therefore examined how four indigenous communities in the Middle Caquetá River region in the Colombian Amazon classify and use natural and anthropogenic soils. The study was framed in ethnopedology: local classifications, preferences, rankings, and soil uses were recorded through interviews and field observations. These communities recognized nine soils varying in suitability for agriculture. They identified anthropogenic soils as most suitable for agriculture, but only one group used them predominantly for their swiddens. As these communities did not perceive soil nutrient status as limiting, they did not base crop-site selection on soil fertility or on the interplay between soil quality and performance of manioc genetic resources.

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During the twentieth century, Amazonia was widely regarded as relatively pristine nature, little impacted by human history. This view remains popular despite mounting evidence of substantial human influence over millennial scales across the region. Here, we review the evidence of an anthropogenic Amazonia in response to claims of sparse populations across broad portions of the region. Amazonia was a major centre of crop domestication, with at least 83 native species containing populations domesticated to some degree. Plant domestication occurs in domesticated landscapes, including highly modified Amazonian dark earths (ADEs) associated with large settled populations and that may cover greater than 0.1% of the region. Populations and food production expanded rapidly within land management systems in the mid-Holocene, and complex societies expanded in resource-rich areas creating domesticated landscapes with profound impacts on local and regional ecology. ADE food production projections support estimates of at least eight million people in 1492. By this time, highly diverse regional systems had developed across Amazonia where subsistence resources were created with plant and landscape domestication, including earthworks. This review argues that the Amazonian anthrome was no less socio-culturally diverse or populous than other tropical forested areas of the world prior to European conquest.

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