bluuebunny/crossref_metadata_2025_split huggingface dataset:
The transparent testa4 Mutation Prevents Flavonoid Synthesis and Alters Auxin Transport and the Response of Arabidopsis Roots to Gravity and Light[W]
Authors: Buer Charles S. , Muday Gloria K. 
Published: May 2004

Abstract
We examined whether flavonoids act as endogenous auxin transport regulators during gravity vector and light intensity changes in Arabidopsis thaliana roots. Flavonoid deficient transparent testa4 [tt4(2YY6)] seedlings had elevated root basipetal auxin transport compared with the wild type, consistent with the absence of a negative auxin transport regulator. The tt4(2YY6) roots had delayed gravitropism that was chemically complemented with a flavonoid intermediate. Flavonoid accumulation was found in wild-type columella cells, the site of gravity perception, and in epidermal and cortical cells, the site of differential growth, but flavonoid accumulation was absent in tt4(2YY6) roots. Flavonoid accumulation was higher in gravity-stimulated root tips as compared with vertical controls, with maximum differences coinciding with the timing of gravitropic bending, and was located in epidermal cells. Exogenous indole-3-acetic acid (IAA) also elevated flavonoid accumulation, suggesting that flavonoid changes in response to gravity might be partly as a result of changing IAA distribution. Acropetal IAA transport was also elevated in roots of tt4(2YY6). Flavonoid synthesis was repressed in the dark, as were differences in root acropetal transport in tt4(2YY6). These results are consistent with light- and gravity-induced flavonoid stimulation that alters auxin transport in roots and dependent physiological processes, including gravitropic bending and root development.
The effect of within‐genet and between‐genet competition on sexual reproduction and vegetative spread in Potentilla anserina ssp. egedii
Authors: RAUTIAINEN PIRJO , KOIVULA KARI , HYVÄRINEN MARKO 
Published: May 2004

Summary

Patterns of biomass allocation to sexual and vegetative reproduction were examined in a perennial stoloniferous clonal plant, Potentilla anserina (L.) Rydb. ssp. egedii (Wormsk.) Hiitonen, in relation to intraspecific competition between monoclonal and multiclonal ramets.
We predicted that a lack of competition would generate allocation to rapid, short‐distance spread (vegetative propagation), while the presence of competition would increase allocation to long‐distance dispersal (sexual reproduction), and that the allocation shift would be more pronounced where the competing ramets were related.
P. anserina ramets were grown in a glasshouse in small pots, either alone (no competition) or with a size‐matched ramet that originated from the same clone (within‐genet competition) or a different one (between‐genet competition).
Competition suppressed both growth and reproduction, but there was no treatment response in relative investment at the level of a whole genet, although both mother ramets and their daughters showed clear effects when analysed separately.
When experiencing competition, the mother ramet allocated relatively more to flowers, whereas allocation to vegetative growth was more intense when competition was absent. Allocation patterns were independent of the relatedness of competitors.
The results imply that P. anserina can modify the allocation of resources to different life‐history traits according to competitive stress. Such flexibility is likely to reflect a shift in the optimal allocation strategy during the life cycle of a plant with a guerilla growth form with rapid exploitation of free space in a new patch by vegetative spread favoured. When spread becomes limited by competition, long‐distance dispersal in space (seeds) or time (persistence) becomes beneficial.
Climatic and landscape controls of the boreal forest fire regime: Holocene records from Alaska
Authors: LYNCH JASON A. , HOLLIS JEREMY L. , HU FENG SHENG 
Published: May 2004

Summary

The response of ecosystems to past and future climatic change is difficult to understand due to the uncertainties in the direction and magnitude of changes and the relative importance of interactions between climate and local factors. In boreal ecosystems such interactions may dictate the response to climatic change, but the interaction of climate, vegetation composition and the fire regime remains poorly understood.
Sediment cores from lakes in south‐central Alaska were analysed for lithology, macrofossils, pollen and charcoal to investigate the relationships between moisture availability, species composition and mean fire return intervals (MFI).
Macrofossil and lithological evidence suggests that variations in effective moisture occurred over the past 7000 years and that the regional climate has been wetter during the past c. 3800 years than before.
Boreal forests existed in the region throughout the past 7000 years. Picea glauca and Picea mariana were the prevalent forest species around Chokasna Lake, whereas P. glauca and hardwood species (e.g. Betula) co‐dominated the landscape around Moose Lake. Picea mariana replaced P. glauca as the dominant Picea species around Chokasna Lake at c. 2000 bp.
MFI was > 500 years before 3800 bp, except from 5800 to 5000 bp at Moose Lake and 5400 to 4550 bp at Chokasna Lake, when values were c. 200 years. MFI decreased to c. 200 years during the late‐Holocene at both sites and to c. 150 years after 2000 bp at Chokasna Lake.
At both sites, fires occurred more frequently under wetter climatic conditions. Our results therefore support other recent studies demonstrating that warmer/drier climatic conditions do not necessarily induce greater fire importance. A combination of increased ignition by lightning strikes and seasonal‐moisture variability probably resulted in more frequent fires under wetter conditions.
The millennial dynamics of a boreal forest stand from buried trees
Authors: ARSENEAULT DOMINIQUE , SIROIS LUC 
Published: May 2004

SummaryWe reconstructed the dynamics of a black spruce (Picea mariana) and jack pine (Pinus banksiana) forest stand in northern Québec using a continuous, 5200‐year‐long sequence of stem remains buried in adjacent peatland. Simulations of recruitment of such remains provided guidelines for inferring past ecosystem structure and composition at the stand scale.Compared with the late Holocene (4650–0 cal. yearBP(CYBP)), the mid Holocene (5200–4650 CYBP) period was characterized by faster tree growth, larger stems and higher stem density, indicating higher forest productivity in association with a milder climate.The presence of stem remains of both species from 17 out of 20 contiguous 250‐year time intervals suggests that the spruce‐pine stand exhibited high compositional stability, with both species regenerating after fire from canopy‐stored seed banks.Relative species abundance closely followed the duration of past fire intervals deduced from the number of tree rings in buried conifers. Time periods of long (4650–3950, 3400–1850 and 250–0 CYBP) and short fire intervals (4950–4650, 3950–3400 and 1850–250 CYBP) were associated, respectively, with decreasing and increasing pine abundance, probably reflecting faster juvenile growth, lower shade tolerance, earlier sexual maturity and shorter longevity in jack pine compared with black spruce.We conclude that both climate change and climate‐induced fire disturbance have been driving long‐term ecosystem dynamics. Our field evidence supports the idea that interactions between disturbances and the life‐history traits of species modulate the impact of climate change at the scale of forest stands. At the same time, disturbances may result in long‐term stability of disturbance‐adapted ecosystems.
Regionalization of methane emissions in the Amazon Basin with microwave remote sensing
Authors: Melack John M. , Hess Laura L. , Gastil Mary , Forsberg Bruce R. , Hamilton Stephen K. , Lima Ivan B.T. , Novo Evlyn M.L.M. 
Published: May 2004

AbstractWetlands of the Amazon River basin are globally significant sources of atmospheric methane. Satellite remote sensing (passive and active microwave) of the temporally varying extent of inundation and vegetation was combined with field measurements to calculate regional rates of methane emission for Amazonian wetlands. Monthly inundation areas for the fringing floodplains of the mainstem Solimões/Amazon River were derived from analysis of the 37 GHz polarization difference observed by the Scanning Multichannel Microwave Radiometer from 1979 to 1987. L‐band synthetic aperture radar data (Japanese Earth Resources Satellite‐1) were used to determine inundation and wetland vegetation for the Amazon basin (<500 m elevation) at high (May–June 1996) and low water (October 1995). An extensive set of measurements of methane emission is available from the literature for the fringing floodplains of the central Amazon, segregated into open water, flooded forest and floating macrophyte habitats. Uncertainties in the regional emission rates were determined by Monte Carlo error analyses that combined error estimates for the measurements of emission and for calculations of inundation and habitat areas. The mainstem Solimões/Amazon floodplain (54–70°W) emitted methane at a mean annual rate of 1.3 Tg C yr−1, with a standard deviation (SD) of the mean of 0.3 Tg C yr−1; 67% of this range in uncertainty is owed to the range in rates of methane emission and 33% is owed to uncertainty in the areal estimates of inundation and vegetative cover. Methane emission from a 1.77 million square kilometers area in the central basin had a mean of 6.8 Tg C yr−1 with a SD of 1.3 Tg C yr−1. If extrapolated to the whole basin below the 500 m contour, approximately 22 Tg C yr−1 is emitted; this mean flux has a greenhouse warming potential of about 0.5 Pg C as CO2. Improvement of these regional estimates will require many more field measurements of methane emission, further examination of remotely sensed data for types of wetlands not represented in the central basin, and process‐based models of methane production and emission.
Radon fluxes in tropical forest ecosystems of Brazilian Amazonia: night‐time CO2 net ecosystem exchange derived from radon and eddy covariance methods
Authors: Martens Christopher S. , Shay Thomas J. , Mendlovitz Howard P. , Matross Daniel M. , Saleska Scott R. , Wofsy Steven C. , Stephen Woodward W. , Menton Mary C. , De Moura José M. S. , Crill Patrick M. , De Moraes Osvaldo L. L. , Lima Risonaldo L. 
Published: May 2004

AbstractRadon‐222 (Rn‐222) is used as a transport tracer of forest canopy–atmosphere CO2 exchange in an old‐growth, tropical rain forest site near km 67 of the Tapajós National Forest, Pará, Brazil. Initial results, from month‐long periods at the end of the wet season (June–July) and the end of the dry season (November–December) in 2001, demonstrate the potential of new Rn measurement instruments and methods to quantify mass transport processes between forest canopies and the atmosphere. Gas exchange rates yield mean canopy air residence times ranging from minutes during turbulent daytime hours to greater than 12 h during calm nights. Rn is an effective tracer for net ecosystem exchange of CO2 (CO2 NEE) during calm, night‐time hours when eddy covariance‐based NEE measurements are less certain because of low atmospheric turbulence. Rn‐derived night‐time CO2 NEE (9.00±0.99 μmol m−2 s−1 in the wet season, 6.39±0.59 in the dry season) was significantly higher than raw uncorrected, eddy covariance‐derived CO2 NEE (5.96±0.51 wet season, 5.57±0.53 dry season), but agrees with corrected eddy covariance results (8.65±1.07 wet season, 6.56±0.73 dry season) derived by filtering out lower NEE values obtained during calm periods using independent meteorological criteria. The Rn CO2 results suggest that uncorrected eddy covariance values underestimate night‐time CO2 loss at this site. If generalizable to other sites, these observations indicate that previous reports of strong net CO2 uptake in Amazonian terra firme forest may be overestimated.
In silico screening of a saturated mutation library of tomato
Authors: Menda Naama , Semel Yaniv , Peled Dror , Eshed Yuval , Zamir Dani 
Published: May 2004

SummaryA comprehensive mutant population is a basic resource for exploring gene function. We developed an isogenic tomato ‘mutation library’ in the genetic background of the inbred variety M82. A total of 13 000 M2 families, derived from EMS (ethyl methane sulfonate) and fast‐neutron mutagenesis, were visually phenotyped in the field and categorized into a morphological catalog that includes 15 primary and 48 secondary categories. Currently, 3417 mutations have been cataloged; among them are most of the previously described phenotypes from the monogenic mutant collection of The Tomato Genetics Resource Center, and over a thousand new mutants, with multiple alleles per locus. The phenotypic database indicates that most mutations fall into more than a single category (pleiotropic), with some organs such as leaves more prone to alterations than others. All data and images can be searched and accessed in the Solanaceae Genome Network (SGN) on a site called ‘The Genes That Make Tomatoes’ (http://zamir.sgn.cornell.edu/mutants/).
Economic Determinants of Multiple Accounting Method Choices in a Swiss Context
Authors: Missonier‐Piera Franck 
Published: May 2004

AbstractThis article investigates economic determinants that may affect multiple accounting method choices made by Swiss listed companies. It intends to make a contribution to the accounting choice literature for at least four reasons. This is, to our knowledge, the first study to investigate the economic determinants of Swiss accounting method choices. Second, Swiss firms provide an interesting sample for testing accounting method choices because they can choose from a much wider range of accounting methods than their American counterparts. Third, this study examines the balance sheet effect as well as the income statement effect. Lastly, multiple accounting methods are used instead of individual choices. The empirical results exhibit that income‐accelerating accounting method choices is positively associated with the recourse to bank and private loans, the extent of assets specificity and the ownership dilution of the firm and negatively with labour force. Additionally, firms that select leverage‐ratios decreasing accounting methods, make higher recourse to debt and especially bank loans to finance their activities and exhibit a higher proportion of specific assets than other corporations. Overall, this result suggests that in a Swiss context, managers may select accounting methods to decrease both debt and political costs as well as to increase their own compensation to some extent.
Protozoa and plant growth: the microbial loop in soil revisited
Authors: Bonkowski Michael 
Published: May 2004

SummaryAll nutrients that plants absorb have to pass a region of intense interactions between roots, microorganisms and animals, termed the rhizosphere. Plants allocate a great portion of their photosynthetically fixed carbon to root‐infecting symbionts, such asmycorrhizal fungi; another part is released as exudates fuelling mainly free‐living rhizobacteria. Rhizobacteria are strongly top‐down regulated by microfaunal grazers, particularly protozoa. Consequently, beneficial effects of protozoa on plant growth have been assigned to nutrients released from consumed bacterial biomass, that is, the ‘microbial loop’. In recent years however, the recognition of bacterial communication networks, the common exchange of microbial signals with roots and the fact that these signals are used to enhance the efflux of carbon from roots have revolutionized our view of rhizosphere processes. Most importantly, effects of rhizobacteria on root architecture seem to be driven in large by protozoan grazers. Protozoan effects on plant root systems stand in sharp contrast to effects of mycorrhizal fungi. Because the regulation of root architecture is a key determinant of nutrient‐ and water‐use efficiency in plants, protozoa provide a model system that may considerably advance our understanding of the mechanisms underlying plant growth and community composition.
Understanding global teleconnections of climate to regional model estimates of Amazon ecosystem carbon fluxes
Authors: Potter Christopher , Klooster Steven , Steinbach Michael , Tan Pang‐Ning , Kumar Vipin , Shekhar Shashi , Carvalho Claudio Reis de 
Published: May 2004

AbstractWe have investigated global teleconnections of climate to regional satellite‐driven observations for prediction of Amazon ecosystem production, in the form of monthly estimates of net carbon exchange over the period 1982–1998 from the NASA–CASA (Carnegie–Ames–Stanford) biosphere model. This model is driven by observed surface climate and monthly estimates of vegetation leaf area index (LAI) and fraction of absorbed PAR (fraction of photosynthetically active radiation, FPAR) generated from the NOAA satellite advanced very high‐resolution radiometer (AVHRR) and similar sensors. Land surface AVHRR data processing using modified moderate‐resolution imaging spectroradiometer radiative transfer algorithms includes improved calibration for intra‐ and intersensor variations, partial atmospheric correction for gaseous absorption and scattering, and correction for stratospheric aerosol effects associated with volcanic eruptions. Results from our analysis suggest that anomalies of net primary production and net ecosystem production predicted from the NASA–CASA model over large areas of the Amazon region east of 60°W longitude are strongly correlated with the Southern Oscillation index. Extensive areas of the south‐central Amazon show strong linkages of the FPAR and the NASA–CASA anomaly record to the Arctic Oscillation index, which help confirm a strong relation to southern Atlantic climate anomalies, with associated impacts on Amazon rainfall patterns. Processes are investigated for these teleconnections of global climate to Amazon ecosystem carbon fluxes and regional land surface climate.
Soil databases and the problem of establishing regional biogeochemical trends
Authors: Holmes Karen W. , Roberts Dar A. , Sweeney Stuart , Numata Izaya , Matricardi Eraldo , Biggs Trent W. , Batista Getulio , Chadwick Oliver A. 
Published: May 2004

AbstractRegional and global environmental modeling depend on soil data for input layers or parameterization. However, randomly located observations, such as provided by agricultural databases, are not always representative of trends identified in field studies conducted under carefully controlled conditions. Many researchers lament the paucity of soil profile data in Amazônia, and suggest that given more data, regional studies would more closely approximate field research results. We assess the ability of a well‐populated regional database collected in the southwestern Brazilian Amazon to reproduce expected biogeochemical trends associated with forest clearing and pasture establishment, and explore the ramifications of relying on independently collected soil data for regional modeling. The Soteron database includes analyses of approximately 3000 soil cores collected for zoning purposes in the state of Rondônia. Pasture ages were determined from a time series of Landsat TM images classified using spectral mixture analysis.Although regional averages showed some of the temporal trends expected based on field study results (e.g. increase in pH following forest clearing), the trends were not statistically significant. Stratification by precipitation and other variables showed pasture age to be important but difficult to separate from other potential controls on soil conditions, mainly because of the reduced number of observations in each stratum. Using multiple regression, which permitted the inclusion of all potential explanatory factors and interactions, pasture age was shown to be a statistically significant predictor of soil conditions. However, the expected temporal sequence of changes documented by field chronosequence studies could not be reproduced. Properties dominated by large‐scale environmental gradients – pH, sum of base cations, aluminum saturation, and exchangeable calcium – were moderately well modeled, while those more strongly linked to dynamic spatially heterogeneous processes such as biological cycling and land management, particularly organic carbon and nitrogen, could not be modeled.Management‐induced soil changes occur at too fine a scale to be captured by most maps, and the relative changes are small compared with spatial heterogeneity caused by controls on soil development over large regions. Therefore, regardless of whether chronosequence‐derived models of biogeochemical response to land‐cover change are correct, the results of these models will not lead to spatially explicit maps that can be validated by regional reconnaissance, nor will they facilitate realistic predictions of the regional biogeochemical consequences of land‐cover change. The change from local to regional scale entails a change in the relative importance of processes controlling soil property behavior.
Variation of carbon and nitrogen cycling processes along a topographic gradient in a central Amazonian forest
Authors: Luizão Regina C. C. , Luizão Flávio J. , Paiva Romilda Q. , Monteiro Terezinha F. , Sousa Lucinéia S. , Kruijt Bart 
Published: May 2004

AbstractIt is well recognized in the literature that topography can influence soil nutrient stocks and dynamics in temperate regions, but for tropical forests, this source of variation has sometimes been ignored. The nature of such variations may depend upon the soil type, which in turn, is closely linked to local or regional topography. This study characterizes the soil and describes the status of carbon and nitrogen in vegetation, litterfall, litter‐layer and soil upper layers along the main positions of a topographic gradient (plateau, slope and valley), 60 km north of Manaus, on Cuieiras Reserve watershed. Nitrogen concentrations in living leaves, fresh litterfall, litter‐layer and soil upper layers were lower in the valley than in both slope and plateau plots. Carbon concentrations in plant material were not significantly different among the three topographic positions, resulting in higher C : N ratios in valley plots. Local topography (plateau, slope and valley) clearly was an influential factor in the nutrient distribution along the study locations. Lower rates of N cycling processes in the valley are probably related to its sandy soil texture and seasonal flooding.