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  • 1
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract De Bruin (1994) noted that, in stable conditions, there exist two solutions of the governing equations of the temperature fluctuation method. By examination of the governing equations, a quantitative description of the nature and behaviour of these solutions is given. The influence of extra sources of temperature variance is discussed, and is shown to lead to an occasional failure of the analysis procedure. The existence of both solutions in the real stably stratified boundary layer is discussed, and evidence is supplied from data collected in a nocturnal boundary layer in Niger, West Africa.
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Ecological orthodoxy suggests that old-growth forests should be close to dynamic equilibrium, but this view has been challenged by recent findings that neotropical forests are accumulating carbon and biomass, possibly in response to the increasing atmospheric concentrations of carbon dioxide. ...
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 416 (2002), S. 594-594 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Rainforests contain not only trees but also lots of water, largely in the form of river systems. The Amazon is by far the largest such system in the world, contributing 20% of all water flowing from rivers to the ocean. But how this and other great rivers participate in the global carbon cycle is a ...
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  • 4
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: 〈list xml:id="l1" style="custom"〉1 Eddy covariance measurements of CO2 flux, based on four and six week campaigns in Rondôdnia, Brazil, have been used in conjunction with a model to scale up data to a whole year, and thus estimate the carbon balance of the tropical forest ecosystem, and the changes in carbon balance expected from small interannual variations in climatological conditions.2 One possible source of error in this estimation arises from the difficulty in measuring fluxes under stably stratified meteorological conditions, such as occur frequently at night. Flux may be ‘lost’ because of low velocity advection, caused by nocturnal radiative cooling at sites on raised ground. Such effects may be detected by plotting the net ecosystem flux of CO2, Feco is a function of wind speed. If flux is ‘lost’ then Feco is expected to decline with wind speed. In the present data set, this did not occur, and Feco was similar to the nocturnal flux estimated independently from chamber measurements.3 The model suggests that in 1992/3, the Gross Primary Productivity (GPP) was 203.3 mol C m−2 y−1 and ecosystem respiration was 194.8 mol C m−2 y−1, giving an ecosystem carbon balance of 8.5 mol C m−2 y−1, equivalent to a sink of 1.0 ton C ha−1 y−1. However, the sign and magnitude of this figure is very sensitive to temperature, because of the strong influence of temperature on respiration.4 The model also suggests that the effect of temperature on the net carbon balance is strongly dependent on the partial pressure of CO2.
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  • 5
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Isoprene is the most abundant volatile hydrocarbon emitted by many tree species and has a major impact on tropospheric chemistry, leading to formation of pollutants and enhancing the lifetime of methane, a powerful greenhouse gas. Reliable estimates of global isoprene emission from different ecosystems demand a clear understanding of the processes of both production and consumption. Although the biochemistry of isoprene production has been studied extensively and environmental controls over its emission are relatively well known, the study of isoprene consumption in soil has been largely neglected.Here, we present results on the production and consumption of isoprene studied by measuring the following different components: (1) leaf and soil and (2) at the whole ecosystem level in two distinct enclosed ultraviolet light-depleted mesocosms at the Biosphere 2 facility: a cottonwood plantation with trees grown at ambient and elevated atmospheric CO2 concentrations and a tropical rainforest, under well watered and drought conditions. Consumption of isoprene by soil was observed in both systems. The isoprene sink capacity of litter-free soil of the agriforest stands showed no significant response to different CO2 treatments, while isoprene production was strongly depressed by elevated atmospheric CO2 concentrations. In both mesocosms, drought suppressed the sink capacity, but the full sink capacity of dry soil was recovered within a few hours upon rewetting. We conclude that soil uptake of atmospheric isoprene is likely to be modest but significant and needs to be taken into account for a comprehensive estimate of the global isoprene budget. More studies investigating the capacity of soils to uptake isoprene in natural conditions are clearly needed.
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  • 6
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: This study investigated the spatial and temporal variation in soil carbon dioxide (CO2) efflux and its relationship with soil temperature, soil moisture and rainfall in a forest near Manaus, Amazonas, Brazil. The mean rate of efflux was 6.45±0.25 SE μmol CO2 m−2s−1 at 25.6±0.22 SE°C (5 cm depth) ranging from 4.35 to 9.76 μmol CO2 m−2s−1; diel changes in efflux were correlated with soil temperature (r2=0.60). However, the efflux response to the diel cycle in temperature was not always a clear exponential function. During period of low soil water content, temperature in deeper layers had a better relationship with CO2 efflux than with the temperature nearer the soil surface. Soil water content may limit CO2 production during the drying-down period that appeared to be an important factor controlling the efflux rate (r2=0.39). On the other hand, during the rewetting period microbial activity may be the main controlling factor, which may quickly induce very high rates of efflux. The CO2 flux chamber was adapted to mimic the effects of rainfall on soil CO2 efflux and the results showed that efflux rates reduced 30% immediately after a rainfall event. Measurements of the CO2 concentration gradient in the soil profile showed a buildup in the concentration of CO2 after rain on the top soil. This higher CO2 concentration developed shortly after rainfall when the soil pores in the upper layers were filled with water, which created a barrier for gas exchange between the soil and the atmosphere.
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  • 7
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The net primary production of tropical forests and its partitioning between long-lived carbon pools (wood) and shorter-lived pools (leaves, fine roots) are of considerable importance in the global carbon cycle. However, these terms have only been studied at a handful of field sites, and with no consistent calculation methodology. Here we calculate above-ground coarse wood carbon productivity for 104 forest plots in lowland New World humid tropical forests, using a consistent calculation methodology that incorporates corrections for spatial variations in tree-size distributions and wood density, and for census interval length. Mean wood density is found to be lower in more productive forests. We estimate that above-ground coarse wood productivity varies by more than a factor of three (between 1.5 and 5.5 Mg C ha−1 a−1) across the Neotropical plots, with a mean value of 3.1 Mg C ha−1 a−1. There appear to be no obvious relationships between wood productivity and rainfall, dry season length or sunshine, but there is some hint of increased productivity at lower temperatures. There is, however, also strong evidence for a positive relationship between wood productivity and soil fertility. Fertile soils tend to become more common towards the Andes and at slightly higher than average elevations, so the apparent temperature/productivity relationship is probably not a direct one. Coarse wood productivity accounts for only a fraction of overall tropical forest net primary productivity, but the available data indicate that it is approximately proportional to total above-ground productivity. We speculate that the large variation in wood productivity is unlikely to directly imply an equivalent variation in gross primary production. Instead a shifting balance in carbon allocation between respiration, wood carbon and fine root production seems the more likely explanation.
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  • 8
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Uncertainty in biomass estimates is one of the greatest limitations to models of carbon flux in tropical forests. Previous comparisons of field-based estimates of the aboveground biomass (AGB) of trees greater than 10 cm diameter within Amazonia have been limited by the paucity of data for western Amazon forests, and the use of site-specific methods to estimate biomass from inventory data. In addition, the role of regional variation in stand-level wood specific gravity has not previously been considered. Using data from 56 mature forest plots across Amazonia, we consider the relative roles of species composition (wood specific gravity) and forest structure (basal area) in determining variation in AGB.Mean stand-level wood specific gravity, on a per stem basis, is 15.8% higher in forests in central and eastern, compared with northwestern Amazonia. This pattern is due to the higher diversity and abundance of taxa with high specific gravity values in central and eastern Amazonia, and the greater diversity and abundance of taxa with low specific gravity values in western Amazonia. For two estimates of AGB derived using different allometric equations, basal area explains 51.7% and 63.4%, and stand-level specific gravity 45.4% and 29.7%, of the total variation in AGB. The variation in specific gravity is important because it determines the regional scale, spatial pattern of AGB. When weighting by specific gravity is included, central and eastern Amazon forests have significantly higher AGB than stands in northwest or southwest Amazonia. The regional-scale pattern of species composition therefore defines a broad gradient of AGB across Amazonia.
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  • 9
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: As part of the Large Scale Biosphere–Atmosphere Experiment in Amazônia (LBA), we have developed a bottom-up approach for estimating canopy-scale fluxes of isoprene. Estimating isoprene fluxes for a given forest ecosystem requires knowledge of foliar biomass, segregated by species, and the isoprene emission characteristics of the individual tree species comprising the forest. In this study, approximately 38% of 125 tree species examined at six sites in the Brazilian Amazon emitted isoprene. Given logistical difficulties and extremely high species diversity, it was possible to screen only a small percentage of tree species, and we propose a protocol for estimating the emission capacity of unmeasured taxa using a taxonomic approach, in which we assign to an unmeasured genus a value based on the percentage of genera within its plant family which have been shown to emit isoprene.Combining this information with data obtained from 14 tree censuses at four Neotropical forest sites, we have estimated the percentage of isoprene-emitting biomass at each site. The relative contribution of each genus of tree is estimated as the basal area of all trees of that genus divided by the total basal area of the plot. Using this technique, the percentage of isoprene-emitting biomass varied from 20% to 42% (mean=31%; SD=8%).Responses of isoprene emission to varying light and temperature, measured on a sun-adapted leaf of mango (Mangifera indica L.), suggest that existing algorithms developed for temperate species are adequate for tropical species as well. Incorporating these algorithms, estimates of isoprene-emitting biomass, isoprene emission capacity, and site foliar biomass into a canopy flux model, canopy-scale fluxes of isoprene were predicted and compared with the above-canopy fluxes measured at two sites. Our bottom-up approach overestimates fluxes by about 50%, but variations in measured fluxes between the two sites are largely explained by observed variation in the amount of isoprene-emitting biomass.
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