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Several hypotheses try to explain the factors that limit the distribution of tree species in wetlands. Among them, the stress-gradient hypothesis states that interspecific ecological interactions (facilitation and competition) vary inversely across abiotic stress gradients, with facilitation being more common under conditions of high abiotic stress than under more benign conditions. We investigated the effects of ecological interactions on the biomass of two native tree species, Crateva tapia (highly flood-tolerant) and Hura crepitans (low flood tolerant) exposed to different experimental flooding conditions in a greenhouse. Individual and paired plants were submitted for 120 days to four treatments: (1) non-flooding and non-ecological interaction; (2) flooding and non-ecological interaction; (3) non-flooding and ecological interaction; (4): flooded and ecological interaction. Flooding reduced biomass allocation in H. crepitans. C. tapia biomass was reduced by interspecific interaction with H. crepitans. Flood and interspecific ecological interactions together facilitated the accumulation of biomass in H. crepitans. Our results support the stress-gradient hypothesis, showing that in a flooded environment, the species with low tolerance to flooding (H. crepitans) is favored by the presence of other species. Additional tests with other species can confirm whether this is a pattern that helps explain the establishment of tree species in wetlands. [ABSTRACT FROM AUTHOR]

Seed transport by hydrochory is a key mechanism of long‐distance dispersal constrained by attributes of the seed and hydrodynamics of the river, influenced by seasonal precipitation and hydrological pulses. However, the extent to which a hydrodynamic model can predict seed dispersal influenced by a tributary is unknown.The study was conducted along a 10‐km stretch of the Falsino River in Amapá, Brazil. Hydrodynamic parameters from the 2021 rainy season were used to calibrate a three‐dimensional numerical model (SisBaHia) and simulate hydrochory of Macrolobium bifolium, a widely distributed species in the Amazon floodplains. This model was coupled with a Lagrangian dispersal model to estimate the average transport distance of the fruit plume. The simulated results were compared statistically with those of dispersal quantified in the field.The field experiment coincided with the maximum hydrological pulse, providing with a maximum potential distance of longitudinal dispersal fruit of c. 10 km in 2 hr. The orders of magnitude of the mean plume transport (observed and numerically simulated centre of mass) were compatible with each other over six longitudinal tracking sections (4.0% ≤ estimated × observed error ≤ 16.5%). Different channel stretches had distinct hydraulic characteristics that influenced spatial dispersal dynamics and are likely to be factors influencing the distribution of M. bifolium in these environments.The present research is a contribution to understanding fluvial hydrodynamics and hydrochory by M. bifolium, whose seed dispersal syndrome is an adaptive characteristic that might explain its abundance and richness in these Amazonian riparian zones. We used M. bifolium as a model species to understand the role of seasonal flood pulse and fluvial hydrodynamics related to hydrochory favouring. [ABSTRACT FROM AUTHOR]

Threats to aquatic mammals may occur in isolation or in combination, leading to cumulative effects on populations and their ecosystems. Thus, conservation actions must consider the complexity of factors involved in patterns of habitat use, including feeding ecology, such as ontogenetic, spatial and temporal dietary shifts.The Amazonian manatee (Trichechus inunguis) occurs in a variety of environments, such as várzeas and igapós (flooded areas) and estuaries. Different environments can lead to variation in the diet of manatees according to the availability and abundance of plant species.Stable isotope analysis (δ13C and δ15N) of manatee teeth was performed to assess spatio‐temporal, ontogenetic and sex‐related patterns in resource use. Mixing models were applied to identify the most consumed plant groups.In várzeas, there were significant interactions between sex and ontogenetic class and ontogenetic class and time series for δ13C values. For manatees sampled from 1994 to 2004, males and adults showed the highest δ15N values, and aquatic C3, followed by C4 plants, were the groups that most contributed to the species' diet.Comparisons among the environments showed the highest δ13C values for manatees from várzeas and the lowest values for manatees from igapós. Várzeas had the highest abundance of C4 plants (high δ13C values), whereas they are scarce in igapós, leading manatees to consume mainly C3 species.The isotopic values of manatees mirrored those of the most available food sources in each environment, supporting the generalist and opportunist behaviour described for the species. Therefore, threats to the diversity, distribution and abundance of aquatic macrophytes, such as contamination, cattle raising and changes in the hydrological cycle (as a consequence of dams and climate change), will affect the diet of the manatee and should be taken into account when designing conservation strategies for the species. [ABSTRACT FROM AUTHOR]

We assessed the feeding habits of the Amazonian manatee inhabiting blackwater (Negro River) and clearwater (Tapajós River) igapós (floodplains) using δ13C and δ15N of dentin and bone collagen from different ontogenetic classes (nursing calves, juveniles, and adults). Within an individual, the dentine δ13C and δ15N values did not vary with tooth position. Bones were more depleted in 13C and 15N compared to teeth, and the δ13C and δ15N in bone differed among classes. Food sources had δ13C values typical of algae, plants of C3 or C4 photosynthetic pathways. Mixing models showed that lactating females (inferred by isotopic values from nursing calves) had higher proportional consumption of C4 plants, while, for other adults, C3 plants were more frequent in the diet of manatees from both rivers. Juveniles had a mixed diet of C3 pants and C4 plants. We hypothesize the C4 plants signal of calves results from female movements to the floodplains of nearby whitewater rivers (várzeas), where C4 plants are abundant. Individuals from Tapajós may be more resident, as C3 plants and C4 plants are available during the flood pulse. Results demonstrate that manatee diets vary with ontogenetic classes and water typology. Preservation of habitats (igapó/várzea) is therefore required for the survival of Amazonian manatees. [ABSTRACT FROM AUTHOR]

The annual and regular flood pulse is the main hydrologic feature found in the large floodplains along Amazonian rivers triggering nutrient cycles, growth rhythms and life cycles of the biota as well as primary and secondary productivity. The construction of hydroelectric dams in the Amazon basin substantially alters the hydrologic regime resulting in severe social, ecological and environmental impacts. While the majority of studies evaluate these impacts in the area of the reservoir and the surroundings of the dam, we focus on disturbances in floodplain forests downstream of the hydroelectric power plant, in this case the Balbina dam, constructed in the 1980s damming the Uatumã River (Central Amazonia). The lowest topographies in the floodplain forests downstream of the dam are dominated by dead trees of Macrolobium acaciifolium (Benth.) Benth. (Fabaceae), a flood-tolerant species forming annual tree rings in consequence of the flood pulse. In this study we evidence alterations in the magnitude and frequency of the hydrologic conditions of the Uatumã River downstream of the hydroelectric power plant comparing the pre-dam (1973–1982) and post-dam (1991–2012) period analyzing a set of biologically relevant hydrologic indicators. To investigate the relationship between the hydrologic changes caused by the dam and the year of death of individuals of M. acaciifolium we use cross-dating techniques (dendrochronology) and radiocarbon dating ( 14 C) as two independent methods. Cross sections of 17 dead individuals were analyzed and individual tree-ring series cross-dated with a well-replicated living trees’ chronology of the same species and region (1804–2012). The outermost tree ring was isolated to perform radiocarbon dating. The dendrochronological and 14 C proxies matched in 88% of the cases, while in the 12% mismatched maximum deviation at least one year. Trees died during periods of consecutive years of inundation, up to two decades after the implementation of the hydroelectric dam. Considering the planning of construction of several dozen dams in the Amazon region there is a critical need to include the downstream impacts in all discussions of hydroelectric implementation. [ABSTRACT FROM AUTHOR]

Background and Aims: In the Amazonian floodplains plants withstand annual periods of flooding which can last 7 months. Under these conditions seedlings remain submerged in the dark for long periods since light penetration in the water is limited. Himatanthus sucuuba is a tree species found in the ‘várzea’ (VZ) floodplains and adjacent non-flooded ‘terra-firme’ (TF) forests. Biochemical traits which enhance flood tolerance and colonization success of H. sucuuba in periodically flooded environments were investigated. [ABSTRACT FROM PUBLISHER]

Comparing plants of the same species thriving in flooded and non-flooded ecosystems helps to clarify the interplay between natural selection, phenotypic plasticity and stress adaptation. We focussed on responses of seeds and seedlings of Genipa americana and Guazuma ulmifolia to substrate waterlogging or total submergence. Both species are commonly found in floodplain forests of Central Amazonia and in seasonally dry savannas of Central Brazil (Cerrado). Although seeds of Amazonian and Cerrado G. americana were similar in size, the germination percentage of Cerrado seeds was decreased by submergence (3 cm water) and increased in Amazonian seeds. The seeds of Amazonian G. ulmifolia were heavier than Cerrado seeds, but germination of both types was unaffected by submergence. Three-month-old Amazonian and Cerrado seedlings of both species survived 30 days of waterlogging or submersion despite suffering significant inhibition in biomass especially if submerged. Shoot elongation was also arrested. Submersion triggered chlorosis and leaf abscission in Amazonian and Cerrado G. ulmifolia while waterlogging did so only in Cerrado seedlings. During 30 days of re-exposure to non-flooded conditions, G. ulmifolia plants that lost their leaves produced a replacement flush. However, they attained only half the plant dry mass of non-flooded plants. Both submerged and waterlogged G. americana retained their leaves. Consequently, plant dry mass after 30 days recovery was less depressed by these stresses than in G. ulmifolia. Small amounts of cortical aerenchyma were found in roots 2 cm from the tip of well-drained plants. The amount was increased by flooding. Waterlogging but not submergence promoted hypertrophy of lenticels at the stem base of both species and adventitious rooting in G. ulmifolia. Despite some loss of performance in dryland plants, flood tolerance traits were present in wetland and dryland populations of both species. They are part of an overall stress-response potential that permits flexible acclimation to locally flooded conditions. [ABSTRACT FROM AUTHOR]