Central Amazon Research Articles

PHYTOPLANKTON BIOMASS INCREASES IN A SILT-IMPACTED AREA IN AN AMAZONIAN FLOOD-PLAIN LAKE OVER 15 YEARS

Tailings from bauxite mining in Porto Trombetas (Pará state, Central Amazonia, Brazil) was discharged (1979–1989) into Batata Lake affecting about 30% of its area. The lake belongs to a clear-water flood-plain system along the Trombetas River, a tributary of the Amazon River. Siltation is the main perceived factor impacting aquatic and flooded communities. Besides natural regeneration, a program to restore a section of igapó forest in the impacted area (IA) has been conducted since 1991. Decreased light is the main factor reducing total phytoplankton biomass (PhyBM) in IA. We hypothesized that PhyBM in IA increases over time because of the improvement of the underwater light conditions due to the natural regeneration and restoration. We sampled quarterly PhyBM and limnological variables (depth, transparency, temperature, pH, conductivity, dissolved oxygen, turbidity, suspended solids, total Kjeldahl nitrogen, and total phosphorus), over 15 years (2005–2019) at eight sampling sites in the two areas (N = 349). We also obtained daily climatic and hydrologic data. PhyBM was higher in NIA than in IA. The temporal trend in the annual mean of PhyBM increased significantly over time only in the IA, approximating the NIA values, confirming our general hypothesis. The increase of PhyBM in the IA was negatively related to the residual light attenuation caused by non-phytoplankton turbidity and to total phosphorus, and positively to air temperature and site depth (p < 0.05; Marginal r2 = 0.18; Conditional r2 = 0.29). Instead, in NIA, PhyBM was explained only by the increase in air temperature (p < 0.05; Marginal r2 = 0.15; Conditional r2 = 0.34). We concluded that the PhyBM in the IA positively responds to the synergy between increasing light availability, air temperature, and site depth, and decreasing total phosphorus concentrations, regardless of hydrologic phase.

Representation of the phosphorus cycle in the Joint UK Land Environment Simulator (vn5.5_JULES-CNP)

Abstract. Most land surface models (LSMs), i.e. the land components of Earth system models (ESMs), include representation of nitrogen (N) limitation on ecosystem productivity. However, only a few of these models have incorporated phosphorus (P) cycling. In tropical ecosystems, this is likely to be important as N tends to be abundant, whereas the availability of rock-derived elements, such as P, can be very low. Thus, without a representation of P cycling, tropical forest response in areas such as Amazonia to rising atmospheric CO2 conditions remain highly uncertain. In this study, we introduced P dynamics and its interactions with the N and carbon (C) cycles into the Joint UK Land Environment Simulator (JULES). The new model (JULES-CNP) includes the representation of P stocks in vegetation and soil pools, as well as key processes controlling fluxes between these pools. We develop and evaluate JULES-CNP using in situ data collected at a low-fertility site in the central Amazon, with a soil P content representative of 60 % of soils across the Amazon basin, to parameterize, calibrate, and evaluate JULES-CNP. Novel soil and plant P pool observations are used for parameterization and calibration, and the model is evaluated against C fluxes and stocks and those soil P pools not used for parameterization or calibration. We then evaluate the model at additional P-limited test sites across the Amazon and in Panama and Hawaii, showing a significant improvement over the C- and CN-only versions of the model. The model is then applied under elevated CO2 (600 ppm) at our study site in the central Amazon to quantify the impact of P limitation on CO2 fertilization. We compare our results against the current state-of-the-art CNP models using the same methodology that was used in the AmazonFACE model intercomparison study. The model is able to reproduce the observed plant and soil P pools and fluxes used for evaluation under ambient CO2. We estimate P to limit net primary productivity (NPP) by 24 % under current CO2 and by 46 % under elevated CO2. Under elevated CO2, biomass in simulations accounting for CNP increase by 10 % relative to contemporary CO2 conditions, although it is 5 % lower compared to CN- and C-only simulations. Our results highlight the potential for high P limitation and therefore lower CO2 fertilization capacity in the Amazon rainforest with low-fertility soils.

Extended-Range Luminescence Dating of Central and Eastern Amazonia Sandy Terrains

The Amazonia biome hosts upland closed and open vegetation ecosystems, in which the current biogeographical patterns relate to the evolution of the physical landscape. Therefore, understanding the origin and timing of the substrates supporting different ecosystems is indispensable for better comprehension of Amazonian biogeography. Here we used quartz optically stimulated luminescence (OSL) and thermally transferred optically stimulated luminescence (TT-OSL) for dating sandy substrates of closed and open vegetation environments in Central and Eastern Amazonia, from both outcrop and drill core samples (Autazes core: PBAT-15-43). These sandy substrates present ages ranging from 1 ka up to almost 2 Ma, that were primarily interpreted as depositional ages of fluvial terraces. Moreover, ages are discussed in terms of potential geomorphic processes leading to the formation of substrates, such as soil mixing and apparent age of quartz from the parent bedrock. The coupling between OSL and TT-OSL techniques allow us to date sedimentary deposits covering the whole Quaternary, which implies a new time window for the Amazonia history.

Functional diversity and trait filtering of insectivorous bats on forest islands created by an Amazonian mega dam

Abstract Mega dams in lowland tropical forests often create large archipelagos, leading to biodiversity decay and disruption of ecosystem functioning in remnant habitat islands. We investigated the functional diversity and functional trait filtering of aerial insectivorous bats in both insular forest patches created by a vast ~30‐year‐old hydropower reservoir and the adjacent mainland continuous forest in Central Amazonia. Bats were surveyed using passive bat recorders across 34 forest sites. Based on a set of morphological traits derived for each species recorded, we estimated both the bat functional richness, functional evenness and functional dispersion at each surveyed site. We further assessed the effects of local vegetation, patch and landscape features on patterns of functional diversity. The interaction between functional traits, environmental characteristics, and species distribution was investigated using a combination of RLQ and fourth‐corner analyses. We found that mainland sites retained higher functional richness and lower functional evenness compared to forest islands, indicating a more complete functional assemblage in the mainland. Additionally, species composition was affected by local vegetation structure and forest area, with small isolated islands exhibiting pervasive loss of functional traits. RLQ and fourth‐corner analyses showed that larger understorey foraging species with greater dispersal capacity, constant frequency–frequency modulated calls, and higher frequency of maximum energy were associated with more isolated small islands. Conversely, forest subcanopy species, exhibiting quasi‐constant frequency calls and presenting low dispersal capacity were associated with continuous forests and islands with greater forest area, and were therefore more sensitive to habitat insularization. Our study calls attention to the pervasive impacts induced by large dams on the functional diversity of tropical insectivorous bats. We recommend that future assessments of the effects of habitat fragmentation on mammals should include traits linked to ecosystem services. In designing and licensing new dams, we suggest the creation of extensive protected areas surrounding mainland forests to minimize the detrimental impacts of small isolated islands and safeguard the full complement of key ecological functions provided by insectivorous bats. Read the free Plain Language Summary for this article on the Journal blog.

Climatic and biotic factors influencing regional declines and recovery of tropical forest biomass from the 2015/16 El Niño

The 2015/16 El Niño brought severe drought and record-breaking temperatures in the tropics. Here, using satellite-based L-band microwave vegetation optical depth, we mapped changes of above-ground biomass (AGB) during the drought and in subsequent years up to 2019. Over more than 60% of drought-affected intact forests, AGB reduced during the drought, except in the wettest part of the central Amazon, where it declined 1 y later. By the end of 2019, only 40% of AGB reduced intact forests had fully recovered to the predrought level. Using random-forest models, we found that the magnitude of AGB losses during the drought was mainly associated with regionally distinct patterns of soil water deficits and soil clay content. For the AGB recovery, we found strong influences of AGB losses during the drought and of [Formula: see text]. [Formula: see text] is a parameter related to canopy structure and is defined as the ratio of two relative height (RH) metrics of Geoscience Laser Altimeter System (GLAS) waveform data-RH25 (25% energy return height) and RH100 (100% energy return height; i.e., top canopy height). A high [Formula: see text] may reflect forests with a tall understory, thick and closed canopy, and/or without degradation. Such forests with a high [Formula: see text] ([Formula: see text] ≥ 0.3) appear to have a stronger capacity to recover than low-[Formula: see text] ones. Our results highlight the importance of forest structure when predicting the consequences of future drought stress in the tropics.

ANÁLISE DA SÉRIE TEMPORAL SENTINEL 1 DE INUNDAÇÕES NA AMAZÔNIA CENTRAL

This study aimed to analyze the dynamics of the flooded areas of the Sentinel 1-SAR time series in a section of the Central Amazon between September 26, 2016, and February 8, 2020. The total of images was 59 for each polarization. In addition, the study calculated the average ordinary flood line (ALOF) from the heights of the fluviometric rulers between the years 1967 to 2020 and compared it with the values present in the radar time series. The pre-processing of the Sentinel-1 time series in the VV and VH polarizations used the following methodological sequence: Apply Orbit File, Radiometric Calibration (σ0), Range-Doppler Terrain Correction, Speckle Filter, and conversion to decibels (dB). The previous analysis of the adaptive filters showed different results for the two polarizations, obtaining the best result for the VV polarization using the Frost filter with 3x3 and the VH polarization with the Lee filter 3x3. The extraction of water bodies and wetlands used a threshold value, making masks for the entire period. The most considerable extent of the floodable area occurred on June 17, 2019, with 6,611.86 km2, representing 16.42% of the SAR scene in the VH polarization and 6,443.19 km2, representing 16.10% of the SAR scene in the VV polarization. The relationship between the VH and VV wetlands to the ruler's height was satisfactory, with coefficients of determination (R2) of 0.79 in the VH polarization and of 0.64 in the VV polarization and a p-value less than 0.05. Keywords: Remote sensing; Radar; Mapping of Water Bodies.

Species density diverges after forest fragmentation in lianescent Machaerium Pers. (Fabaceae) in Central Amazonia

Liana density is positively associated with forest fragmentation. The process of colonization by lianas is often reported without considering species composition, and consequent changes in liana species composition is relatively unexplored. To understand the compositional change associated with disturbance, we inventoried lianas in permanent plots of the Biological Dynamics of Forest Fragments Project (BDFFP), north of Manaus, Central Amazonia, Brazil. This analysis was focused exclusively on species of the diverse genus Machaerium Pers. (Fabaceae). All lianas with DBH ≥ 2 cm were marked, measured, collected, and identified to the species level in 34 1-ha plots, distributed in continuous and fragmented forests. Density data were analyzed at three hierarchical taxonomic levels: the whole liana community, the genus Machaerium, and each species within Machaerium. At both the generic and species levels, we calculated absolute and relative density. Density (absolute and relative) was evaluated using two indicators of forest disturbance: (1) continuous versus fragmented forest, and (2) plot proximity to forest edge. We employed Generalized Linear Mixed Model with Template Model Builder for analyses. As expected, whole community liana density was positively related to forest disturbance. However, absolute density of the genus Machaerium was not affected by edge or by forest fragmentation, and consequently relative density of the genus Machaerium was reduced. Among the eight species of Machaerium, we found distinct patterns of response to disturbance. Absolute densities of M. hoehneanum and M. aureiflorum were positively affected by forest disturbance, similar to the pattern of the whole liana community, while absolute densities for M. macrophyllum and M. ferox were negatively affected. Absolute densities of the other four species (M. madeirense, M. leiophyllum, M. multifoliolatum, and M. quinata) were not affected by fragmentation indicators. The relative density of six of the eight Machaerium species was negatively affected by forest fragmentation. The variation of responses in closely related species of lianas suggests that liana species are neither uniformly nor always positively affected by forest fragmentation.

Climate changes and the formation of fluvial terraces in central Amazonia inferred from landscape evolution modeling

Abstract. Climate changes have been considered an essential factor controlling the shaping of the recent alluvial landscapes in central Amazonia, with implications for explaining the biogeographic patterns in the region. This landscape is characterized by wide floodplains and various terrace levels at different elevations. A set of older terraces with ages between 50 and >200 ka occupy the higher portions of central Amazonia, whereas multiple terraces next to floodplains occur at lower elevations and display ages of a few thousand years. These lower terraces, referred to as middle–lower terraces, reveal what can be perceived as a stochastic pattern both in space and time. Despite the widespread occurrence of these geomorphic features, no process-oriented analysis has been conducted to explain their formation. Here, we develop a landscape evolution model referred to as SPASE (Sedimentary Processes and Alluvial Systems Evolution) to explicitly account for fluvial erosion and deposition in combination with lateral channel migration to explore the controls on terrace development. The model results show that the higher terraces were deposited under the condition of a higher base level for the basins upstream of the confluence between the Solimões and Negro rivers. The subsequent decrease in the base level initiated a phase of gradual incision, thereby resulting in the current fluvial configuration. The model also predicts that high-frequency climate changes resulted in the construction of middle–lower terraces at various elevations which, however, are all situated at lower elevation than the higher terrace levels. Our model shows that dry-to-wet shifts in climate, in relation to the modern situation, yield a landscape architecture where middle–lower terrace levels are better preserved than wet-to-dry changes in climate, again if the current situation is considered as reference. Finally, our results show that fast and widespread landscape changes possibly occurred in response to high-frequency climate changes in central Amazonia, at least since the Late Pleistocene, with great implications for the distribution and connectivity of different biotic environments in the region. Because of this short timescale of response to external perturbations, we suggest that the streams in central Amazonia possibly also respond in rapid and sensitive ways to human perturbations.

Evolution of an Amazonian Fish Is Driven by Allopatric Divergence Rather Than Ecological Divergence

Lowland central Amazonia is characterized by heterogeneous riverscapes dominated by two chemically divergent water types: black (ion-poor, rich in dissolved organic carbonate and acidic) and white (rich in nutrient and turbid) waters. Recent phylogeographic and genomic studies have associated the ecotone formed by these environments to an ecologically driven genetic divergence between fish present in both water types. With the objective of better understanding the evolutionary forces behind the central Amazonian teleostean diversification, we sampled 240 Mesonauta festivus from 12 sites on a wide area of the Amazonian basin. These sites included three confluences of black and white water environments to seek for repeated evidences of ecological divergence at the junction of these ecotones. Results obtained through our genetic assessment based on 41,268 single nucleotide polymorphism (SNPs) contrast with previous findings and support a low influence of diverging water physicochemical characteristics on the genetic structuration of M. festivus populations. Conversely, we detected patterns of isolation by downstream water current and evidence of past events of vicariance potentially linked to the Amazon River formation. Using a combination of population genetics, phylogeographic analysis and environmental association models, we decomposed the spatial and environmental genetic variances to assess which evolutionary forces shaped inter-population differences in M. festivus’ genome. Our sampling design, comprising three confluences of black and white water rivers, supports the main role of evolution by allopatry. While an ecologically driven evolution admittedly played a role in Amazonian fish diversification, we argue that neutral evolutionary processes explain most of the divergence between M. festivus populations.

Soil moisture thresholds explain a shift from light-limited to water-limited sap velocity in the Central Amazon during the 2015–16 El Niño drought

Transpiration is often considered to be light- but not water-limited in humid tropical rainforests due to abundant soil water, even during the dry seasons. The record-breaking 2015–16 El Niño drought provided a unique opportunity to examine whether transpiration is constrained by water under severe lack of rainfall. We measured sap velocity, soil water content, and meteorological variables in an old-growth upland forest in the Central Amazon throughout the 2015–16 drought. We found a rapid decline in sap velocity (−38 ± 21%, mean ± SD.) and in its temporal variability (−88%) during the drought compared to the wet season. Such changes were accompanied by a marked decline in soil moisture and an increase in temperature and vapor pressure deficit. Sap velocity was largely limited by net radiation during the wet and normal dry seasons; however, it shifted to be primarily limited by soil moisture during the drought. The threshold in which sap velocity became dominated by soil moisture was at 0.33 m3 m−3 (around −150 kPa in soil matric potential), below which sap velocity dropped steeply. Our study provides evidence for a soil water threshold on transpiration in a moist tropical forest, suggesting a shift from light limitation to water limitation under future climate characterized by increased temperature and an increased frequency, intensity, duration and extent of extreme drought events.

Phylogeny, infrageneric classification and historical biogeography of Mesochila Rivalier, 1969 (Coleoptera: Cicindelidae), with the performance of different phylogenetic inferences using morphological data compared

In this study, we aim to understand the boundaries and the species evolutionary relationships in Mesochila, which includes 20 species arranged into three subgenera. We also conducted a biogeographic analysis that allowed us to identify the major events that shaped the currently disjunct distribution of the group. Our analyses were performed employing four major phylogenetic algorithms: equal and implied weight parsimony, maximum likelihood and Bayesian inference. Phylogenetic analyses, including 25 taxa (all 20 species in the genus plus five outgroups) and 37 characters, indicated that Mesochila is a monophyletic group composed of four strongly supported lineages, although no consensus was attained regarding relationships between lineages. Bayesian inference resulted in the less resolved topology, whereas implied weight parsimony yielded the most different tree when using a low k value (1). We present a new infrageneric classification for the group with the description of Mesochila (Neomesochila)subgen. nov. to accommodate M. (N.) brevipennis, M. (N.) drechseli, M. (N.) moraveci, and M. (N.) prepusula. Furthermore, we transfer M. (M.) distincta from M. (Eumesochila) back to M. (Mesochila). The biogeographical analysis suggested a South American origin for the group, in Chacoan/Paraná dominions (Atlantic rainforest/Cerrado biomes), with subsequent dispersions to Central America and Amazonia.

Negative seroprevalence for Toxoplasma gondii in free-living primates from Central Amazonia.

This study presents 35 negative serologies for antibodies anti-T.gondii in free-living primates from Central Amazonia. Our results suggest that these populations have not had contact with the parasite and, therefore, do not have antibodies. This was the first study surveying T.gondii in Cacajao, Callicebus, Pithecia, and Saguinus monkeys.

A comparison of the spatial heterogeneities of surface fluxes simulated by INLAND model with observations at a valley and a nearby plateau stations in Central Amazon Forest

An improved version of the Integrated Land Surface Model (INLAND), incorporating the physical, ecological and hydrological parameters and processes pertaining to two subclasses of tropical forest in the central Amazon basin, a poorly drained flat plateau and a well-drained adjacent broad valley, is used to simulate the hydrological, energy and CO2 fluxes. The model is forced with observed meteorological data. The experimental output data from the model runs are compared with observational data at the two locations. The seasonal variabilities of water table depth at the valley site and the soil moisture at the plateau site are satisfactorily simulated. The two locations exhibit large differences in energy, carbon and water fluxes, both in the simulations and in the observations. Results validate the INLAND model and indicate the need for incorporating sub-grid scale variability in the relief, soil type and vegetation type attributes to improve the representation of the Amazonian ecosystems in land-surface models.

Satellite Analyses Unravel the Multi-Decadal Impact of Dam Management on Tropical Floodplain Vegetation

An assessment of river regulation impact on floodplain vegetation is crucial to developing a modern watershed management approach in the Neotropics aimed at mitigating alterations of the floodplain environment. Floodplain forest monitoring requires high–resolution mapping, as vegetation dynamics are in the narrow area at the interface between terrestrial and aquatic systems. The existing satellite images that afford land observations have limitations due to coarse resolution or gaps in data caused by the extreme cloudiness of tropical regions. This study provides a new framework for high-resolution mapping and monitoring of a large-scale tropical forest in the aquatic-terrestrial zone of an Amazon basin. The main aim is to assess the vegetation status and the environmental degradation in a highly altered fluvial setting. To achieve the goal, a remote sensing processing chain, which couples hydrologic and vegetation data, was developed. A map of high-resolution traditional vegetation indices and their non-linear generalization was derived from the high-resolution gap-free reflectance data obtained by combining Landsat and MODIS data, through the HISTARFM algorithm. Subsequently, hydrological modification within these areas was assessed by using a global water surface dataset. In addition, the impact of river regulation on riverine forest carbon cycling was assessed through the analysis of interannual variability of the gross primary production of floodplain vegetation. The framework was applied to analyze the last 2 decades of changes in the floodplain forest of Uatumã river (central Amazon basin), downstream of the Balbina hydropower dam built in 1987. The analysis showed the presence of vegetation degradation in areas of increased hydrologic stress and upland forest encroachment in areas no longer inundated. The dam continues to have effects on vegetation even 30 years after its construction. The ongoing profound reshuffling of the floodplain forest, and the impact on the carbon storage capacity of the floodplain forest suggest that the situation is far from a new environmental equilibrium. The proposed high–resolution approach allows for a detailed mapping of riparian vegetation alterations, helping to develop a more careful management of the watershed through a better understanding of the human footprint on floodplain forests.

Cenozoic weathering of fluvial terraces and emergence of biogeographic boundaries in Central Amazonia

The study of paleofluvial dynamics is crucial to understand the role of rivers as biogeographic boundaries in Amazonia during the Cenozoic. In central Amazonia, Mesozoic and Cenozoic fluvial deposits - Alter do Chão, Iranduba and Novo Remanso Formations - host supergene iron oxides and record changes in the distribution of flooded and non-flooded (upland) environments. Geochronological data on these deposits are still scarce to constrain past landscape changes. Therefore, in this study we investigate iron oxides precipitated within weathering profiles developed on ancient fluvial terraces to access the interplay between flooded and non-flooded environments in central Amazonia. We aimed to trace the history of abandonment of alluvial plains and the subsequent weathering of lowland sediment deposits during the Cenozoic. We identified at least two main periods of iron oxide precipitation: (1) one starting before ~42 Ma and ending at ~18 Ma; and (2) a well-defined humid and weathering prone phase between ~8 and 1 Ma. Dominant goethite precipitation marks a major climatic shift towards more humid conditions from ~3 Ma. The increase in water discharge of the Negro and Solimões rivers possibly promoted fluvial incision and conversion of floodplains into long-lasting upland terrains as indicated by the development of lateritic weathering profiles. This major phase of upland expansion corroborates upland birds phylogenetic data, which indicate the emergence of a major biogeographic barrier in central Amazonia during late Pliocene/Pleistocene. • Refining the age of the fluvial sedimentary units in central Amazonia • Multiple Cenozoic discrete weathering phases in central Amazonia • Linking weathering phases with fluvial landscape changes • Constraining the emergence of a major biogeographic boundary

Temporal and Spatial Stability on the Population Structure of Consumed and Illegally Traded Big-Headed Amazon River Turtle in the Negro River Basin, Central Amazon, Brazil

Freshwater turtles are a valuable food resource for riverine human communities and have been historically overharvested throughout all major tropical large river basins, with consequent gradual population decreases. Even species considered to be abundant are declining, and in many cases were brought to a condition of near extinction. The collection of adult females during breeding season on nesting beaches is considered a major factor in population decline and subsequent loss of food sources for humans. There is growing consensus that adult females constitute the category which turtle populations can least afford to lose. In the Negro River Basin, the podocnemidid big-headed Amazon River turtle,Peltocephalus dumerilianus, is heavily exploited for consumption and poached for illegal trade among riverine communities and cities. Between 1997 and 2002 and in 2019, we measured live turtles and carapaces of big-headed turtles in the city of Barcelos and its surroundings, and among the riverine families living in the Jaú National Park. We compared body sizes and sex ratios between areas, periods, and between consumed and traded individuals. We found no differences between areas, even those close to Barcelos and the ones belonging to remote areas where pressure levels are lower. The individuals consumed in Jaú National Park are larger than those poached for illegal trade in both areas. There was an increase in average size between 1997 and 2002. Sex ratio was slightly skewed toward males, which were larger, and did not differ between areas and periods. Results indicate stability on size of harvested populations, which may be supporting current extraction levels. Data suggest this could be related to the absence of adult female capture during nesting for this species. We recommend protection strategies for other Amazon Podocnemidid species that focus on the protection of nesting beaches and surrounding areas where adults occupy, specifically in areas under communal protection.

Turbulent transport and reactions of plant-emitted hydrocarbons in an Amazonian rain forest

The processes governing the temporal and spatial patterns of isoprene and monoterpenes emitted by a rainforest in the central Amazon region of Brazil is investigated using a combination of field experiments and numerical simulations. Specifically, Large Eddy Simulations (LES) were used to resolve emissions of isoprene and monoterpenes, turbulent transport, and air chemistry. The coupled chemistry-transport LES included the effects of isoprene and monoterpenes reactivity due to reactions with hydroxyl radical and ozone. The LES results are used to compute vertically resolved budgets of isoprene and monoterpenes in the rainforest canopy in response to emissions, turbulent transport, surface deposition, and air chemistry. Results indicated that emission and dispersion dominated the isoprene budget as the gases were transported out of the canopy space. In a region limited by nitrogen oxides (with prevailing nitric oxide levels of < 0.5 parts per billion), the in-canopy chemical destruction removed approximately 10% of locally emitted monoterpenes. Hydroxyl radical production rates from the ozonolysis of monoterpenes amounted to ≈2×106radicalscm−3s−1 and had similar magnitude to the light-dependent hydroxyl radical formation. One key conclusion was that the Amazonia rainforest abundantly emitted monoterpenes whose in-canopy ozonolysis yielded hydroxyl radicals in amounts similar to the magnitude of light-dependent formation. Reactions of monoterpenes and isoprene with hydroxyl radical and ozone were necessary for the maintenance of the Amazon rainforest canopy as a photochemically active environment suitable to generate oxidants and secondary organic aerosols.

Biochar After Thirteen Years of Agricultural Crops on the Physical Attributes and Organic Carbon of a Yellow Oxisol in Central Amazon

Biochar has been identified as a conditioner for the physical, chemical and biological properties of the soil. In this perspective, it is reckoned that when added in the long term, this material may condition improvements in the physical properties of agricultural soils. As a result, the objective of this work was to quantify changes in the physical attributes of the soil after thirteen years of the addition of biochar in a Yellow Dystrophic Oxisol in Central Amazon, in the agricultural ecosystem in Brazil. In a thirteen-year experiment (2006-2019) with rotation of agricultural crops, the physical properties of a clayey Yellow Oxisol with the addition of increasing doses of biochar, were studied. The experiment was conducted in randomized blocks, with four replications and four treatments, making up sixteen experimental units with a size of 10 m &amp;times; 10 m (100 m2). The analysis of the results did not indicate a positive effect on most of the physical attributes studied, however, there was significance only for two sets of data. Compared to soil without biochar, there was a decrease in the density of soil particles, and an increase in soil resistance to penetration into the surface layer, in soil with biochar. No difference was found in the subsurface layer for all evaluated attributes.

Hydro-Edaphic Gradient and Phylogenetic History Explain the Landscape Distribution of a Highly Diverse Clade of Lianas in the Brazilian Amazon

Plant distribution patterns may indicate habitat specialization either by closely related species with conserved traits or by phylogenetically distant species with converging traits. Lianas represent a large proportion of the overall tropical species diversity and abundance. Despite their importance, little is known about the relationship between habitat specialization and the phylogenetic structure of lianas, especially at the landscape scale where forest disturbances and hydro-edaphic gradients are crucial. To explore this knowledge gap, we used one of the most diverse lineages of Neotropical lianas to test whether (i) landscape environmental gradients explain liana species diversity and composition, (ii) habitat specialization is phylogenetically conserved along ecological gradients, and (iii) closely related liana species have more similar distribution patterns. We hypothesized that hydro-edaphic and forest disturbance gradients determine the compartmentalization of a subset of closely related species in different portions of the ecological gradients. To test our hypothesis, we examined the distribution of the tribe Bignonieae on 34 1-ha permanent plots systematically distributed over a 42 km2 forested landscape area in Central Amazon. We used proxies for the hydro-edaphic, forest disturbance, and soil nutrient gradients. Liana diversity increased along the hydro-edaphic gradient (i.e., toward dry plateaus), but slightly decreased along the forest disturbance gradient. Further, we found evidence of habitat specialization along the hydro-edaphic gradient on plateaus with deeper water tables, where liana assemblages are subsets of closely related species, exhibiting phylogenetic clustering. The opposite pattern was found on valleys, where liana assemblages were phylogenetically overdispersed. Our results support the role of phylogenetic niche conservatism on plateaus and a stronger environmental filter within the hydrologically dynamic valleys, associated with a functional convergence of more distantly related species. The selection of more distantly related species on hydrologically dynamic areas is a general pattern among trees, palms and now lianas. We conclude that ecological filters and phylogenetic history have played fundamental roles in structuring liana assemblages unevenly at the landscape scale. Fine-scale hydrology determines several aspects of plant community organization, whose mechanisms need to be experimentally investigated in the Amazon basin.

Wildmeat consumption and child health in Amazonia

Consuming wildmeat may protect against iron-deficiency anemia, a serious public health problem globally. Contributing to debates on the linkages between wildmeat and the health of forest-proximate people, we investigate whether wildmeat consumption is associated with hemoglobin concentration in rural and urban children (< 5 years old) in central Brazilian Amazonia. Because dietary practices mediate the potential nutritional benefits of wildmeat, we also examined whether its introduction into children’s diets is influenced by rural/urban location or household socio-economic characteristics. Sampling 610 children, we found that wildmeat consumption is associated with higher hemoglobin concentration among the rural children most vulnerable to poverty, but not in the least vulnerable rural, or urban children. Rural caregivers share wildmeat with children earlier-in-life than urban caregivers, potentially because of cultural differences, lower access to domesticated meat, and higher wildmeat consumption by rural households (four times the urban average). If wildmeat becomes unavailable through stricter regulations or over-harvesting, we predict a ~ 10% increased prevalence of anemia among extremely poor rural children. This modest protective effect indicates that ensuring wildmeat access is, alone, insufficient to control anemia. Sustainable wildlife management could enhance the nutritional benefits of wildlife for vulnerable Amazonians, but reducing multidimensional poverty and improving access to quality healthcare are paramount.