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  • 1
    Electronic Resource
    Electronic Resource
    Hydrological variability, organic matter supply and denitrification in the Garonne River ecosystem (2004)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 49 (2004), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Groundwater nitrate contamination has become a worldwide problem as increasing amounts of nitrogen fertilisers are used in agriculture. Alluvial groundwater is uniquely juxtaposed between soils and streams. Hydrological connections among these subsystems regulate nutrient cycling.2. We measured denitrification using an in situ acetylene-block assay in a nitrate-contaminated portion of the Garonne River catchment along a gradient of surface water–ground water mixing during high (snowmelt) and low flow.3. During high flow (mid-April to early June) the water table rose an average of 35 cm and river water penetrated the subsurface to a great extent in monitoring wells. Denitrification rates averaged 5.40 μgN2O L−1 min−1 during the high flow period, nearly double the average rate (2.91 μgN2O L−1 min−1) measured during base flow. This was driven by a strong increase in denitrification in groundwater under native riparian vegetation. Nitrate concentrations were significantly lower during high flow compared with base flow. Riparian patches had higher dissolved organic carbon concentrations that were more aromatic compared with the gravel bar patch closest to the river.4. Multiple linear regression showed that the rate of denitrification was best predicted by the concentration of low molecular weight organic acids. These molecules are probably derived from decomposition of soil organic matter and are an important energy source for anaerobic respiratory processes like denitrification. The second best predictor was per cent surface water, reflecting higher denitrification rates during spring when hydrological connection between surface water and ground water was greatest.5. Our results indicate that, while denitrification rates in Garonne River alluvium were spatially and temporally variable, denitrification was a significant NO3 sink during transport from the NO3-contaminated floodplain to the river. DOC availability and river–floodplain connectivity were important factors influencing observed spatial and temporal patterns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2426.2003.01175.x
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  • 2
    Electronic Resource
    Electronic Resource
    Variation in wood density determines spatial patterns inAmazonian forest biomass (2004)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 10 (2004), S. 0 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.2004.00751.x
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  • 3
    Electronic Resource
    Electronic Resource
    Variation in potential for isoprene emissions among Neotropical forest sites (2004)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 10 (2004), S. 0 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1529-8817.2003.00760.x
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  • 4
    Electronic Resource
    Electronic Resource
    The above-ground coarse wood productivity of 104 Neotropical forest plots (2004)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 10 (2004), S. 0 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1529-8817.2003.00778.x
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  • 5
    Electronic Resource
    Electronic Resource
    Differential lifetime success and performance of native and non-native Atlantic salmon examined under communal natural conditions (2004)
    Oxford, UK; Malden, USA : Blackwell Science Ltd
    Journal of fish biology 65 (2004), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The lifetime success and performance characteristics of communally reared offspring of wild native Burrishoole (native), ranched native (ranched) and non-native (non-native) Atlantic salmon Salmo salar from the adjacent Owenmore River were compared. Non-native 0+ year parr showed a substantial downstream migration, which was not shown by native and ranched parr. This appears to have been an active migration rather than competitive displacement and may reflect an adaptation to environmental or physiographic conditions within the Owenmore River catchment where the main nursery habitat is downstream of the spawning area. There were no differences between native and ranched in smolt output or adult return. Both of these measures, however, were significantly lower for the non-native group. A greater proportion of the non-native Atlantic salmon was taken in the coastal drift nets compared to the return to the Burrishoole system, probably as a result of the greater size of the non-native fish. The overall lifetime success of the non-native group, from fertilized egg to returning adult, was some 35% of native and ranched. The ranched group showed a significantly greater male parr maturity, a greater proportion of 1+ year smolts, and differences in sex ratio and timing of freshwater entry of returning adults compared to native, which may have fitness implications under specific conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0022-1112.2004.00557.x
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  • 6
    Electronic Resource
    Electronic Resource
    Body condition and reproductive capacity of three-spined stickleback infected with the cestode Schistocephalus solidus (2004)
    Oxford, UK; Malden, USA : Blackwell Science Ltd
    Journal of fish biology 64 (2004), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The relationship between reproductive ability and the residual index of body condition in three-spined stickleback Gasterosteus aculeatus from a population infected with the cestode macroparasite Schistocephalus solidus in Walby Lake, Alaska, was examined. In general, reproductive activities resulted in significantly lower levels of body condition in three-spined stickleback during the latter part of the breeding season, and relatively high levels of S. solidus infection intensified the energetic drain. Although female body condition did not differ significantly due just to the presence of S. solidus, increased parasite index did have a significant negative effect on female body condition. Males showed significantly lower levels of body condition in response to S. solidus infection alone and in association with a greater parasite index. Males had greater mean parasite indices than females. Females had significantly lower body condition than males, which may be due to discrepancies in energy expenditure between the sexes during reproduction. Females with greater body condition were significantly more likely to produce a clutch of eggs than those with lower condition, suggesting a threshold effect of body condition on reproductive capacity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0022-1112.2004.00411.x
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  • 7
    Electronic Resource
    Electronic Resource
    An in vivo inducible gene of Pseudomonas aeruginosa encodes an anti-ExsA to suppress the type III secretion system (2004)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 54 (2004), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have previously reported on the isolation of in vivo inducible genes of Pseudomonas aeruginosa using IVET system. One of such genes isolated from burn mouse infection model encodes a short open reading frame with unknown function. In this study, we demonstrate that this gene product specifically suppresses the expression of type III secretion genes in P. aeruginosa, thus named PtrA (Pseudomonas type III repressor A). A direct interaction between the PtrA and type III transcriptional activator ExsA was demonstrated, suggesting that its repressor function is probably realized through inhibition of the ExsA protein function. Indeed, an elevated expression of the exsA compensates the repressor effect of the PtrA. Interestingly, expression of the ptrA is highly and specifically induced by copper cation. A copper- responsive two-component regulatory system, copR-copS, has also been identified and shown to be essential for the copper resistance in P. aeruginosa as well as the activation of ptrA in response to the copper signal. Elevated expression of the ptrA during the infection of mouse burn wound suggests that P. aeruginosa has evolved tight regulatory systems to shut down energy-expensive type III secretion apparatus in response to specific environmental signals, such as copper stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.2004.04282.x
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  • 8
    Electronic Resource
    Electronic Resource
    Structure, function and evolution of microbial adenylyl and guanylyl cyclases (2004)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 52 (2004), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Cells respond to signals of both environmental and biological origin. Responses are often receptor mediated and result in the synthesis of so-called second messengers that then provide a link between extracellular signals and downstream events, including changes in gene expression. Cyclic nucleotides (cAMP and cGMP) are among the most widely studied of this class of molecule. Research on their function and mode of action has been a paradigm for signal transduction systems and has shaped our understanding of this important area of biology. Cyclic nucleotides have diverse regulatory roles in both unicellular and multicellular organisms, highlighting the utility and success of this system of molecular communication. This review will examine the structural diversity of microbial adenylyl and guanylyl cyclases, the enzymes that synthesize cAMP and cGMP respectively. We will address the relationship of structure to biological function and speculate on the complex origin of these crucial regulatory molecules. A review is timely because the explosion of data from the various genome projects is providing new and exciting insights into protein function and evolution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.2004.04067.x
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