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Amazonian headwater streams trail a heterogeneous landscape, with marked natural variation of geomorphological conditions and hydrological periods. Southern Brazilian Amazon is subjected to high degradation pressure, mainly from deforestation. Hence, we characterize pristine headwaters structure (hydromorphology and water physical-chemical variables) and variation among hydrological periods (dry, beginning of the rainy period and end of the rainy period), to define reference conditions for conservation-oriented classification, monitoring and rehabilitation of the southern Brazilian Amazon streams. Stretches of 10 pristine streams from the Teles Pires River, a major tributary of the Tapajós River, were analysed for hydromorphology, water physical-chemical variables and controlled for habitat integrity (forested proportion on buffer zones and habitat integrity index). We found variation among hydrological periods and spatial heterogeneity on pristine stream structure. Most variables showed great variation ranges at the same hydrological period and high variation coefficient values, reflecting the natural environmental heterogeneity among streams protected by a riparian forest. Variation among hydrological periods and spatial heterogeneity between streams in this region, combined with current high levels of deforestation, indicates the need for the conservation of a high proportion of streams and their respective riparian forests. Here, we have presented reference range values for monitoring and rehabilitation programs integrated in the Amazonian aquatic conservation efforts. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The effect of root inundation on the leaf emissions of ethanol, acetaldehyde and acetic acid in relation to assimilation and transpiration was investigated with 2-3 years old tree seedlings of four Amazonian floodplain species by applying dynamic cuvette systems under greenhouse conditions. Emissions were monitored over a period of several days of inundation using a combination of Proton Transfer Reaction Mass Spectrometry (PTR-MS) and conventional techniques (HPLC, ion chromatography). Under non-flooded conditions, none of the species exhibited measurable emissions of any of the compounds, but rather low deposition of acetaldehyde and acetic acid was observed instead. Tree species specific variations in deposition velocities were largely due to variations in stomatal conductance. Flooding of the roots resulted in leaf emissions of ethanol and acetaldehyde by all species, while emissions of acetic acid were only observed from the species exhibiting the highest ethanol and acetaldehyde emission rates. All three compounds showed a similar diurnal emission profile, each displaying an emission burst in the morning, followed by a decline in the evening. This concurrent behavior supports the conclusion, that all three compounds emitted by the leaves are derived from ethanol produced in the roots by alcoholic fermentation, transported to the leaves with the transpiration stream and finally partly converted to acetaldehyde and acetic acid by enzymatic processes. Co-emissions and peaking in the early morning suggest that root ethanol, after transportation with the transpiration stream to the leaves and enzymatic oxidation to acetaldehyde and acetate, is the metabolic precursor for all compounds emitted, though we can not totally exclude other production pathways. Emission rates substantially varied among tree species, with maxima differing by up to two orders of magnitude (25-1700 nmol m-2 min-1 for ethanol and 5-500 nmol m-2 min-1 for acetaldehyde). Acetic acid emissions reached 12 nmol m-2 min-1. The observed differences in emission rates between the tree species are discussed with respect to their root adaptive strategies to tolerate long term flooding, providing an indirect line of evidence that the root ethanol production is a major factor determining the foliar emissions. Species which develop morphological root structures allowing for enhanced root aeration produced less ethanol and showed much lower emissions compared to species which lack gas transporting systems, and respond to flooding with substantially enhanced fermentation rates and a non-trivial loss of carbon to the atmosphere. The pronounced differences in the relative emissions of ethanol to acetaldehyde and acetic acid between the tree species indicate that not only the ethanol production in the roots but also the metabolic conversion in the leaf is an important factor determining the release of these compounds to the atmosphere. [ABSTRACT FROM AUTHOR]

Astrocaryum jauari is the most frequent palmin the floodplains (igapó) of the Rio Negro, in Brazilian Amazonia. It grows to 20 m of height and is rarely found isolated. More commonly, 4-6 individuals of different sizes stand together which originate from the same rhizome. Fruit abscission occurs at highest water levels and dispersal occurs by fish. The palm has commercial value: until 1998, for 20 years 'palmito' was the basis of the industrial production in Central Amazonia. In the present study, seasonal dynamics and biomass of fruit production in A. jauari are described in relation to water level and annual flood duration. Systematic studies were performed at the Ecological Station of the Anavilhanas Archipelago, with an inventory area covering 5.000 m². Fruit production was monitored at weekly intervals and biomass was determined. Data on the dispersing fishes was obtained by collection in the field and by interviews of local people. A. jauari occurs from the higher levels to the lowest in the flooding gradient, being waterlogged up to 270-340 days/year. 125 individuals of A. jauari occorred in the sampled 5.000 m², which is equivalent to a density of 250 ind/ha in the Anavilhanas. Only adult trees which were directly exposed to light produced fruits. 16 species of fish feed on the fruits of A. jauari. Ten of these act as possible dispersers, 3 as predators. The high contents of vitamine A may be attractive for the fishes. Since the fruits do not have structures enhancing floatation, hydrochoric dispersal does not occur and the seeds succumb to the hypoxic conditions under water. In habitats with short periods of flooding, the fruits may be accumulated near the adult plant (barochory). Other trees occurring in the habitats colonized by A. jauari have hydrochoric and ichthyochoric dispersal syndromes and show high flooding tolerance. In the main area of extractivism of the past, in the Município Barcelos, the density of the species varied between the islands, and had densities between 250 and 2.000 ind/ha. Here, one worker could fell up to 90 palms at high water (May, June) and up to 25 in the low water period (december, january). For each tree, 0.5 to 1 bin of processed bin of "palmito" is produced. Assuming a mean number of ten workers in the area, 900 to 250 palms are exploited per day, corresponding to 1-0.5 ha destroyed forest. If we consid the densities of the palm and its productivity as calculated for the Anavilhanas islands (whcih was 165 kg), extractivism without replacement of new palm trees implies a fast extinction and exclusion of this ressource for the ichthyofauna of the archipelago with all consequences for the local people. [ABSTRACT FROM AUTHOR]

Fluxes of CO2 and H2O vapour from dense stands of the C4 emergent macrophyte grass Echinochloa polystachya were measured by eddy covariance in both the low water (LW) and high water (HW, flooded) phases of the annual Amazon river cycle at Manaus, Brazil. Typical clear-sky midday CO2 uptake rates by the vegetation stand (including detritus, sediment or water surface) were 30 and 35 µmol CO2 (ground) m–2 s–1 in the LW and HW periods, respectively. A rectangular hyperbola model fitted the responses of "instantaneous" (20- or 30-min average) net CO2 exchange rates to incident photosynthetic photon flux densities (PFD) well. Stand evaporation rates were linearly related to PFD. The major difference in CO2 uptake rates between the two periods was the larger respiration flux during LW due to the CO2 efflux from sediment, roots and litter. Integrated 20- or 30-min fluxes were used to derive relationships between daily CO2 and H2O vapour fluxes and incident radiation. The daily CO2 fluxes were almost linearly related to incident radiation, but there was evidence of saturation at the highest daily radiation totals. Annual productivity estimated from the daily model in 1996–1997 agreed closely with that previously estimated for 1985–1986 from a leaf-scale photosynthetic model, but were some 15% less than those derived at that time from biomass harvests. Both CO2 uptake and water use efficiency were comparable with those found in fertilised maize fields in warm temperate conditions. [ABSTRACT FROM AUTHOR]

Echinochloa polystachya forms extensive monotypic stands on the lower levels of the Amazon floodplains. During its annual growth cycle c.100 t (dry mass) ha{sup}-1{end} of biomass is formed as the floodplain is being submerged (December--September) and a phase of death and decomposition occurs when the water has retreated (October- -November). This study examines the mineral nutrient dynamics of this plant and its potential significance to the nutrient status of the flood plain. Echinochloa polystachya was sampled monthly from a study site in the central Amazon. N, P and K contents for different plant organs were determined and net uptake calculated from concurrent measurements of dry matter production and turnover. Leaf N, P and K contents were c. 20, 1.7 and 19 g kg{sup}-1{end}, values typical of nutrient-repletestands of C{sub}4{end} plants. Stem concentrations were c. 12% of those of the leaves. Net N and P uptake followed the rise in the river level, whilst K appeared independent of water level. The vegetation accumulated 377, 51 and 1136 kg ha{sup}-2{end} of N, P and K, respectively, during the growth phase. Over a possible 5000 km{sup}2{end} of these stands in the Varzea, this represents a massive sequestration of nutrients in the flood phase and a high release during the following low-water period. It is suggested that the E. polystachya stands could have a role in maintaining the nutrient status of the Amazon floodplain. [ABSTRACT FROM AUTHOR]

Attalea excelsa (urucurizeiro) is a dominant palm of the estuarine floodplains, with great potential for nontimber management. This study evaluated the population dynamics of urucurizeiro and the factors that contribute to colonising of this species in a flooded environment. Individuals with base height circumference ≥ 30 cm in 2011 and 2014 were measured in 55.95 ha of floodplain forest in southern Amapá, Brazil. The parameters of population dynamics (mortality, recruitment and growth) in high and low floodplain environments were determined. Ripley's K function was used to analyse the spatial distribution. Population density in 2011 was 3.99 individual ha-1, and in 2014 the density increased to 4.09 individual ha-1. Mortality rate was zero and the recruitment rate was 1.05% year-1. Basal area in 2011 was 0.49 m² ha-1 and in 2014, it reached 0.72 m² ha-1. Diameter growth rate was 5.32 cm year-1. The population presented an aggregate distribution pattern. Structural differences in diameter (F = 9.15, p = 0.003) and basal area (F = 10.7, p = 0.001) were evident between high and low floodplain forests. The increase in diameter was higher in low floodplain (3.98 cm year-1) compared with high floodplain (1.35 cm year-1). The patterns shown by A. excelsa are reflections of its high adaptation to the daily flooded environment. [ABSTRACT FROM AUTHOR]

Pentaclethra macroloba is a hyperdominant species with multiple uses in the Amazon. This species tolerates varying flood amplitudes, however the effect of flood topographic gradient on its ecophysiology remains unclear. We want to know if individuals from the high (10 trees) and low (20 trees) várzea show distinct phenological patterns as a function of the flood gradient, as well as their colonization strategies and their seed predators. From February 2018 to December 2019, we monitored the phenology of P. macroloba. There was no difference in phenological patterns between the two environments, but flooding caused different phenological responses. The increase in temperature favored the production of flower buds and increased precipitation reduced the proportion of flowering trees in both environments. The increase in rainfall and river flood level favored the ripe fruit only in the low várzea where individuals were most exposed to flooding. When the flood level increased, there was a greater proportion of trees losing leaves in both environments. The species produces high variability in seed size (length: H = 49.2, p > 0.001; width: H = 62.5, p > 0.001; weight: H = 70.4, p > 0.001). The seed predation rate was 5%, mainly caused by Carmenta surinamensis moth larva. The flood gradient established different phenological responses in the species, directing trees to have a better reproductive performance. The low predation rate and the variability in seed size are factors that contribute to the formation of large population densities in the Amazon River estuary.

Fluxes of CO 2 and H 2 O vapour from dense stands of the C4 emergent macrophyte grass Echinochloa polystachya were measured by eddy covariance in both the low water (LW) and high water (HW, flooded) phases of the annual Amazon river cycle at Manaus, Brazil. Typical clear-sky midday CO 2 uptake rates by the vegetation stand (including detritus, sediment or water surface) were 30 and 35 µmol CO 2  (ground) m -2  s -1 in the LW and HW periods, respectively. A rectangular hyperbola model fitted the responses of "instantaneous" (20- or 30-min average) net CO 2 exchange rates to incident photosynthetic photon flux densities (PFD) well. Stand evaporation rates were linearly related to PFD. The major difference in CO 2 uptake rates between the two periods was the larger respiration flux during LW due to the CO 2 efflux from sediment, roots and litter. Integrated 20- or 30-min fluxes were used to derive relationships between daily CO 2 and H 2 O vapour fluxes and incident radiation. The daily CO 2 fluxes were almost linearly related to incident radiation, but there was evidence of saturation at the highest daily radiation totals. Annual productivity estimated from the daily model in 1996-1997 agreed closely with that previously estimated for 1985-1986 from a leaf-scale photosynthetic model, but were some 15% less than those derived at that time from biomass harvests. Both CO 2 uptake and water use efficiency were comparable with those found in fertilised maize fields in warm temperate conditions.