People, soil and manioc interactions in the upper Amazon region

Abstract Clara Patricia Peña Venegas (2015). People, soil and manioc interactions in the upper Amazon region. PhD thesis, Wageningen University, The Netherlands, with summaries in English and Dutch, 210 pp. The presence of anthropogenic soils, or Amazonian Dark Earths (ADE), fuels the debate about how pristine the Amazon ecosystem actually is, and about the degree to which humans affected Amazonian diversity in the past. Most upland soils of the Amazon region are very acid, highly weathered, and have a limited nutrient holding capacity; together, these characteristics limit permanent or intensive agriculture. Várzeas or floodplains that are periodically enriched with Andean sediments carried and deposited by rivers that cross the Amazon Basin, are moderately fertile but experience periodic floods that limit agriculture to crops able to produce in a short time. ADE patches in uplands usually are more fertile than non-anthropogenic uplands, providing a better environment for agriculture. Most studies about how people manage a broad portfolio of natural and anthropogenic soils come from non-indigenous farmers of Brazil. There is limited information about how indigenous people use a broad soil portfolio, and how this affects the diversity of their staple crop, manioc. With the aim to contribute to the understanding of the role of ADE in indigenous food production, as compared with other soils, and in order to provide information about how indigenous people use and create diversity in Amazonia, research was carried out among five different ethnic groups living in two locations of the Colombian Amazon. Several social and natural science methods were used during the study. These included ethnography, participant observation, structured and un-structured interviews, sampling of soil and manioc landraces, standardized protocols for the quantification of soil physical and chemical variables, and molecular techniques to assess genetic diversity of manioc and arbuscular mycorrhizal fungi. Results indicate that ADE patches from the Middle Caquetá region of Colombia are not contrastingly more fertile than surrounding, non-anthropogenic upland soils, except for higher levels of available phosphorus in ADE. Indigenous farmers from the Middle Caquetá region do not use ADE more frequently or more intensively than non-ADE uplands. The swidden agriculture practiced on ADE and on non-ADE uplands is similar. Although ADE patches were not specifically important for swiddens and therefore relatively unimportant for the production of manioc. They were important as sites for indigenous settlements and for maintaining agroforestry systems with native and exotic species that do not grow in soils with low available phosphorus. Várzeas were also used for agriculture, whether farmers had access to ADE or not. Differences occurred between locations in the type of floodplains selected and the way they were cultivated. Those differences were not related to differences in soil conditions but were associated with the cultural traditions of the different ethnic groups who cultivate low floodplains, as well as labor availability when organizing collective work (mingas) to harvest floodplains. Manioc diversity among indigenous communities was not predominantly related with differences in soil types. Complete manioc stocks were cultivated equally on ADE, non-ADE uplands or várzeas. One issue that could be related with this non-specificity in manioc-soil combinations was the similar arbuscular mycorrhizal fungi diversity of soils and the high number of arbuscular mycorrhizal symbionts associated to manioc roots; these were shown to be independent from the physicochemical composition of the soil or the manioc landrace. Differences in the diversity of manioc stocks among ethnic groups were predominantly related to cultural values attached to different manioc landraces. This study of indigenous agriculture in environments with natural and anthropogenic soils indicates that people have had an important role in transforming the Amazonian ecosystem through agriculture, with consequences on forest composition and forest dynamics. Pre-Columbian people contributed to this by creating an additional soil- the Amazonian Dark Earths. Although ADE are not presently considered to play a major role in indigenous food production, indigenous people believe that ADE have had an important role in the management of the first maniocs cultivated by their ancestors. The domestication of manioc and the creation and maintenance of hundreds of different landraces by indigenous people contributed, and still contributes, to the region’s plant diversity.</p

People, soil and manioc interactions in the upper Amazon region

Abstract Clara Patricia Peña Venegas (2015). People, soil and manioc interactions in the upper Amazon region. PhD thesis, Wageningen University, The Netherlands, with summaries in English and Dutch, 210 pp. The presence of anthropogenic soils, or Amazonian Dark Earths (ADE), fuels the debate about how pristine the Amazon ecosystem actually is, and about the degree to which humans affected Amazonian diversity in the past. Most upland soils of the Amazon region are very acid, highly weathered, and have a limited nutrient holding capacity; together, these characteristics limit permanent or intensive agriculture. Várzeas or floodplains that are periodically enriched with Andean sediments carried and deposited by rivers that cross the Amazon Basin, are moderately fertile but experience periodic floods that limit agriculture to crops able to produce in a short time. ADE patches in uplands usually are more fertile than non-anthropogenic uplands, providing a better environment for agriculture. Most studies about how people manage a broad portfolio of natural and anthropogenic soils come from non-indigenous farmers of Brazil. There is limited information about how indigenous people use a broad soil portfolio, and how this affects the diversity of their staple crop, manioc. With the aim to contribute to the understanding of the role of ADE in indigenous food production, as compared with other soils, and in order to provide information about how indigenous people use and create diversity in Amazonia, research was carried out among five different ethnic groups living in two locations of the Colombian Amazon. Several social and natural science methods were used during the study. These included ethnography, participant observation, structured and un-structured interviews, sampling of soil and manioc landraces, standardized protocols for the quantification of soil physical and chemical variables, and molecular techniques to assess genetic diversity of manioc and arbuscular mycorrhizal fungi. Results indicate that ADE patches from the Middle Caquetá region of Colombia are not contrastingly more fertile than surrounding, non-anthropogenic upland soils, except for higher levels of available phosphorus in ADE. Indigenous farmers from the Middle Caquetá region do not use ADE more frequently or more intensively than non-ADE uplands. The swidden agriculture practiced on ADE and on non-ADE uplands is similar. Although ADE patches were not specifically important for swiddens and therefore relatively unimportant for the production of manioc. They were important as sites for indigenous settlements and for maintaining agroforestry systems with native and exotic species that do not grow in soils with low available phosphorus. Várzeas were also used for agriculture, whether farmers had access to ADE or not. Differences occurred between locations in the type of floodplains selected and the way they were cultivated. Those differences were not related to differences in soil conditions but were associated with the cultural traditions of the different ethnic groups who cultivate low floodplains, as well as labor availability when organizing collective work (mingas) to harvest floodplains. Manioc diversity among indigenous communities was not predominantly related with differences in soil types. Complete manioc stocks were cultivated equally on ADE, non-ADE uplands or várzeas. One issue that could be related with this non-specificity in manioc-soil combinations was the similar arbuscular mycorrhizal fungi diversity of soils and the high number of arbuscular mycorrhizal symbionts associated to manioc roots; these were shown to be independent from the physicochemical composition of the soil or the manioc landrace. Differences in the diversity of manioc stocks among ethnic groups were predominantly related to cultural values attached to different manioc landraces. This study of indigenous agriculture in environments with natural and anthropogenic soils indicates that people have had an important role in transforming the Amazonian ecosystem through agriculture, with consequences on forest composition and forest dynamics. Pre-Columbian people contributed to this by creating an additional soil- the Amazonian Dark Earths. Although ADE are not presently considered to play a major role in indigenous food production, indigenous people believe that ADE have had an important role in the management of the first maniocs cultivated by their ancestors. The domestication of manioc and the creation and maintenance of hundreds of different landraces by indigenous people contributed, and still contributes, to the region’s plant diversity

Classification and Use of Natural and Anthropogenic Soils by Indigenous Communities of the Upper Amazon Region of Colombia

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.</p

Differences in manioc diversity among five ethnic groups of the Colombian Amazon

Manioc is an important root crop in the tropics and the most important staple food in the Amazon. Manioc is diverse but its diversity has not yet been clearly associated with environmental or social factors. Our study evaluates how variation in edaphic environments and in social factors influences manioc diversity among five ethnic groups of the Amazon region of Colombia. Inventories of landraces, genetic analysis of manioc diversity, visits to farmers’ swiddens and interviews with farmers were carried out during two years of field work. Morphotypic and genotypic diversity of manioc were large. The different ethnic groups of our study cultivate different sweet and bitter manioc landraces which they select and maintain in accordance with their ancestral rules and norms. Differences in available environments among indigenous communities (such as the presence of different soils) did not markedly affect manioc morphotypic or genotypic diversity, while social factors considerably influenced observed manioc diversity. Manioc diversity was explained by two parallel processes of manioc diversification: volunteer seedling selection and manioc seed exchange. We argue that, for a full understanding of manioc diversity, indigenous knowledge, as well as morphological and genetic variation should be taken into account

Temperature and pH define the realised niche space of arbuscular mycorrhizal fungi

The arbuscular mycorrhizal (AM) fungi are a globally distributed group of soil organisms that play critical roles in ecosystem function. However, the ecological niches of individual AM fungal taxa are poorly understood. We collected > 300 soil samples from natural ecosystems worldwide and modelled the realised niches of AM fungal virtual taxa (VT; approximately species‐level phylogroups). We found that environmental and spatial variables jointly explained VT distribution worldwide, with temperature and pH being the most important abiotic drivers, and spatial effects generally occurring at local to regional scales. While dispersal limitation could explain some variation in VT distribution, VT relative abundance was almost exclusively driven by environmental variables. Several environmental and spatial effects on VT distribution and relative abundance were correlated with phylogeny, indicating that closely related VT exhibit similar niche optima and widths. Major clades within the Glomeraceae exhibited distinct niche optima, Acaulosporaceae generally had niche optima in low pH and low temperature conditions, and Gigasporaceae generally had niche optima in high precipitation conditions. Identification of the realised niche space occupied by individual and phylogenetic groups of soil microbial taxa provides a basis for building detailed hypotheses about how soil communities respond to gradients and manipulation in ecosystems worldwide