bluuebunny/crossref_metadata_2025_split huggingface dataset:
Velocity analysis after migration
Authors: Silva Ron , Wang Yanghua 
Published: March 2003

The double‐square‐root (DSR) equation used in pre‐stack migration is formulated in terms of velocity‐dependent and velocity‐independent terms. The velocity‐dependent term is shown to be the hyperbolic normal moveout (NMO) correction, whereas the velocity‐independent term is related to the recording geometry only. This separation of the velocity‐dependent term offers a means of applying vertical corrections to an initial migration velocity field. Using this concept, procedures are described both for velocity determination and for achieving improved structural imaging.This decoupling is accurate both for constant‐velocity media and for media whose velocity varies as a function of depth. In media whose velocity varies as a function of both space and depth, a procedure is described for building velocity models through common‐image gather (CIG) stacking following prestack depth migration (PSDM) and time conversion (TC). This so‐called PSDM‐TC stack procedure provides a means of (a) incorporating both vertical and lateral velocity updates into an initial velocity model, (b) obtaining improved structural imaging by using a non‐optimal velocity model for the prestack depth migration, and (c) updating velocity by flattening CIGs and maximizing stack energy. The procedure can be applied to both P‐P wave and P‐SV wave migration.
Experimental soil warming effects on CO2 and CH4 flux from a low elevation spruce–fir forest soil in Maine, USA
Authors: RUSTAD LINDSEY E. , FERNANDEZ IVAN. J. 
Published: March 2003

AbstractThe effect of soil warming on CO2 and CH4 flux from a spruce–fir forest soil was evaluated at the Howland Integrated Forest Study site in Maine, USA from 1993 to 1995. Elevated soil temperatures (∼5 °C) were maintained during the snow‐free season (May – November) in replicated 15 × 15‐m plots using electric cables buried 1–2 cm below the soil surface; replicated unheated plots served as the control. CO2 evolution from the soil surface and soil air CO2 concentrations both showed clear seasonal trends and significant (P < 0.0001) positive exponential relationships with soil temperature. Soil warming caused a 25–40% increase in CO2 flux from the heated plots compared to the controls. No significant differences were observed between heated and control plot soil air CO2 concentrations which we attribute to rapid equilibration with the atmosphere in the O horizon and minimal treatment effects in the B horizon. Methane fluxes were highly variable and showed no consistent trends with treatment.
The influence of increasing growth temperature and CO2 concentration on the ratio of respiration to photosynthesis in soybean seedlings
Authors: ZISKA LEWIS H. , BUNCE JAMES A. 
Published: March 2003

AbstractUsing controlled environmental growth chambers, whole plants of soybean, cv. ‘Clark’, were examined during early development (7–20 days after sowing) at both ambient (≈ 350 μL L–1) and elevated (≈ 700 μL L–1) carbon dioxide and a range of air temperatures (20, 25, 30, and 35 °C) to determine if future climatic change (temperature or CO2 concentration) could alter the ratio of carbon lost by dark respiration to that gained via photosynthesis. Although whole‐plant respiration increased with short‐term increases in the measurement temperature, respiration acclimated to increasing growth temperature. Respiration, on a dry weight basis, was either unchanged or lower for the elevated CO2 grown plants, relative to ambient CO2 concentration, over the range of growth temperatures. Levels of both starch and sucrose increased with elevated CO2 concentration, but no interaction between CO2 and growth temperature was observed. Relative growth rate increased with elevated CO2 concentration up to a growth temperature of 35 °C. The ratio of respiration to photosynthesis rate over a 24‐h period during early development was not altered over the growth temperatures (20–35 °C) and was consistently less at the elevated relative to the ambient CO2 concentration. The current experiment does not support the proposition that global increases in carbon dioxide and temperature will increase the ratio of respiration to photosynthesis; rather, the data suggest that some plant species may continue to act as a sink for carbon even if carbon dioxide and temperature increase simultaneously.
Carbon accumulation, distribution and water use of Danthonia richardsonii swards in response to CO2 and nitrogen supply over four years of growth
Authors: LUTZE JASON L. , GIFFORD ROGER M. 
Published: March 2003

AbstractMicrocosms of Danthonia richardsonii (Cashmore) accumulated more carbon when grown under CO2 enrichment (719 μL L–1 cf. 359 μL L–1) over a four‐year period, even when nitrogen availability severely restricted productivity (enhancement ratios for total microcosm C accumulation of 1.21, 1.14 and 1.29 for mineral N supplies of 2.2, 6.7 and 19.8 g N m–2 y–1, respectively). The effect of CO2 enrichment on total system carbon content did not diminish with time. Increased carbon accumulation occurred despite the development over time of a lower leaf area index and less carbon in the green leaf fraction at high CO2. The extra carbon accumulated at high CO2 in the soil, senesced leaf and leaf litter fractions at all N levels, and in root at high‐N, while at low‐and mid‐N less carbon accumulated in the root fraction at high CO2. The rate of leaf turnover was increased under CO2 enrichment, as indicated by increases in the carbon mass ratio of senesced to green leaf lamina. Microcosm evapotranspiration rates were lower at high CO2 when water was in abundant supply, resulting in higher average soil water contents. The higher soil water contents at high CO2 have important implications for microcosm function, and may have contributed significantly to the increased carbon accumulation at high CO2. These results indicate that CO2 enrichment can increase carbon accumulation by a simple soil–plant system, and that any increase in whole system carbon accumulation may not be evident from snapshot measurements of live plant carbon.
Using an ecosystem model linked to GCM‐derived local weather scenarios to analyse effects of climate change and elevated CO2 on dry matter production and partitioning, and water use in temperate managed grasslands
Authors: Riedo Marcel , Gyalistras Dimitrios , Fischlin Andreas , Fuhrer JürG. 
Published: March 2003

AbstractLocal effects of climate change (CC) and elevated CO2 (2 × CO2, 660 μmol mol–1) on managed temperate grasslands were assessed by forcing a dynamic ecosystem model with weather scenarios. The aims of the study were to compare the relative importance of individual and combined effects of CC, 2 × CO2, and photosynthetic acclimation, and to assess the importance of local site conditions. The model was driven by hourly means for temperature (T), precipitation (P), global radiation (G), vapour pressure (VP), and wind speed (U). Local climate scenarios were derived by statistical downscaling techniques from a 2 × CO2 simulation with the General Circulation Model of the Canadian Climate Centre (CCC‐GCMII). Simulations over 14 growing seasons to account for year‐to‐year variability of climate were carried out for a low, relatively dry site, and a high, more humid site.At both sites, shoot dry matter responded positively to 2 × CO2 with the site at low elevation being more sensitive than the higher site. The effect of assumed changes in climate was negative at the lower, but positive at the higher site. Shoot dry matter was more sensitive to the effects of 2 × CO2 than to CC. Both effects combined increased shoot dry matter by up to 20%. This was attributed to direct effects of 2 × CO2 and increased T, and indirect stimulation via increased soil N availability. Biomass partitioning to roots increased with 2 × CO2 but decreased with CC, while an intermediate response resulted from the combination. Leaf area index (LAI) increased under 2 × CO2, but not enough to compensate fully for a decrease in leaf conductance. Under the 2 × CO2 scenario evapotranspiration (ET) decreased, but increased under CC. Photosynthetic acclimation reduced the effect of 2 × CO2 on shoot growth, but had little effect on ET. The seasonal water use efficiency (WUE) was improved under 2 × CO2, and reduced under CC. With the combination of both factors, the change was small but still positive, especially at the high elevation site with more favourable soil water conditions. This reflects the stronger positive yield response in combination with a smaller increase in ET under cooler, more humid conditions.The results for the combination of factors suggest that except for shoot growth, effects of 2 × CO2 and CC tend to offset each other. While CC determines the sign of the ET response, the sign of the biomass response is determined by 2 × CO2. The results highlight the importance of a site‐specific analysis of ecosystem responses by using a flexible approach based on a combination of state‐of‐the‐art downscaling, spatially resolved data sets, and a mechanistic model to obtain quantitative and reproducible assessments of climate change impacts at the ecosystem level.
A thirty percent increase in UV‐B has no impact on photosynthesis in well‐watered and droughted pea plants in the field
Authors: Allen D. J. , Nogués S. , Morison J. I. L. , Greenslade P. D. , Mcleod A. R. , Baker N. R. 
Published: March 2003

AbstractIt has been suggested that field experiments which increase UV‐B irradiation by a fixed amount irrespective of ambient light conditions (‘square‐wave’), may overestimate the response of photosynthesis to UV‐B irradiation. In this study, pea (Pisum sativum L.) plants were grown in the field and subjected to a modulated 30% increase in ambient UK summer UV‐B radiation (weighted with an erythemal action spectrum) and a mild drought treatment. UV‐A and ambient UV control treatments were also studied. There were no significant effects of the UV‐B treatment on the in situ CO2 assimilation rate throughout the day or on the light‐saturated steady‐state photosynthesis. This was confirmed by an absence of UV‐B effects on the major components contributing to CO2 assimilation; photosystem II electron transport, ribulose 1,5‐bisphosphate regeneration, ribulose 1,5‐bisphosphate carboxylase/oxygenase carboxylation, and stomatal conductance. In addition to the absence of an effect on photosynthetic activities, UV‐B had no significant impact on plant biomass, leaf area or partitioning. UV‐B exposure increased leaf flavonoid content. The UV‐A treatment had no observable effect on photosynthesis or productivity. Mild drought resulted in reduced biomass, a change in partitioning away from shoots to roots whilst maintaining leaf area, but had no observable effect on photosynthetic competence. No UV‐B and drought treatment interactions were observed on photosynthesis or plant biomass. In conclusion, a 30% increase in UV‐B had no effects on photosynthetic performance or productivity in well‐watered or droughted pea plants in the field.
Impulse response functions of terrestrial carbon cycle models: method and application
Authors: Thompson Matthew V. , Randerson James T. 
Published: March 2003

AbstractTo provide a common currency for model comparison, validation and manipulation, we suggest and describe the use of impulse response functions, a concept well‐developed in other fields, but only partially developed for use in terrestrial carbon cycle modelling. In this paper, we describe the derivation of impulse response functions, and then examine (i) the dynamics of a simple five‐box biosphere carbon model; (ii) the dynamics of the CASA biosphere model, a spatially explicit NPP and soil carbon biogeochemistry model; and (iii) various diagnostics of the two models, including the latitudinal distribution of mean age, mean residence time and turnover time. We also (i) deconvolve the past history of terrestrial NPP from an estimate of past carbon sequestration using a derived impulse response function to test the performance of impulse response functions during periods of historical climate change; (ii) convolve impulse response functions from both the simple five‐box model and the CASA model against a historical record of atmospheric δ13C to estimate the size of the terrestrial 13C isotopic disequilibrium; and (iii) convolve the same impulse response functions against a historical record of atmospheric 14C to estimate the 14C content and isotopic disequilibrium of the terrestrial biosphere at the 1° × 1° scale. Given their utility in model comparison, and the fact that they facilitate a number of numerical calculations that are difficult to perform with the complex carbon turnover models from which they are derived, we strongly urge the inclusion of impulse response functions as a diagnostic of the perturbation response of terrestrial carbon cycle models.
Emissions of carbon from forestry and land‐use change in tropical Asia
Authors: Houghton R. A. , Hackler J. L. 
Published: March 2003

AbstractThe net emissions of carbon from forestry and changes in land use in south and southeast Asia were calculated here with a book‐keeping model that used rates of land‐use change and associated per hectare changes in vegetation and soil to calculate changes in the amount of carbon held in terrestrial ecosystems and wood products. The total release of carbon to the atmosphere over the period 1850–1995 was 43.5 PgC. The clearing of forests for permanent croplands released 33.5 PgC, about 75% of the total. The reduction of biomass in the remaining forests, as a result of shifting cultivation, logging, fuelwood extraction, and associated regrowth, was responsible for a net loss of 11.5 PgC, and the establishment of plantations withdrew from the atmosphere 1.5 PgC, most of it since 1980. Based on comparisons with other estimates, the uncertainty of this long‐term flux is estimated to be within ±30%. Reducing this uncertainty will be difficult because of the difficulty of documenting the biomass of forests in existence >40 years ago. For the 15‐y period 1981–1995, annual emissions averaged 1.07 PgC y–1, about 50% higher than reported for the 1980s in an earlier study. The uncertainty of recent emissions is probably within ± 50% but could be reduced significantly with systematic use of satellite data on changes in forest area. In tropical Asia, the emissions of carbon from land‐use change in the 1980s accounted for approximately 75% of the region’s total carbon emissions. Since 1990 rates of deforestation and their associated emissions have declined, while emissions of carbon from combustion of fossil fuels have increased. The net effect has been a reduction in emissions of CO2 from this region since 1990.
Effects of elevated ultraviolet radiation on Quercus robur and its insect and ectomycorrhizal associates
Authors: Newsham K. K. , Greenslade P. D. , Mcleod A. R. 
Published: March 2003

SummarySaplings of pedunculate oak (Quercus robur L.) were exposed at an outdoor facility to modulated levels of elevated UV‐B radiation (280–315 nm) under treatment arrays of cellulose diacetate‐filtered fluorescent lamps which also produced UV‐A radiation (315–400 nm). Saplings were also exposed to UV‐A radiation alone under control arrays of polyester‐filtered lamps and to ambient levels of solar radiation under arrays of unenergized lamps. The UV‐B treatment corresponded to a 30% elevation above the ambient level of erythemally weighted UV‐B radiation. Sapling growth and the occurrence of associated organisms were examined over two years. In both years, leaves of saplings exposed to UV‐B treatment were thicker and smaller in area relative to leaves exposed to ambient and control levels of radiation. UV‐B treatment also retarded bud burst at one sampling in the first year of the study. Some responses were recorded which were common to both treatment and control arrays, implying that UV‐A radiation, or some other factor associated with energized lamps, was responsible for the observed effects. Saplings under treatment and control arrays were taller in the first year of the study, suffered greater herbivory from chewing insects, and had lower root dry weights and greater insertion heights of secondary branches than saplings exposed to ambient levels of radiation. Exposure of saplings to elevated UV‐A radiation alone under control arrays increased estimated leaf volumes in the second year of the study and reduced the number of secondary branches and the total number of branches per sapling after two years, relative to both treatment and ambient arrays. There were no effects of elevated ultraviolet radiation on shoot or total plant weight, root/shoot ratios, stem diameter, the numbers or insertion heights of primary or tertiary branches, total leaf number, timing of leaf fall or frequency of ectomycorrhizas. Our study suggests that any increases in UV‐B radiation as a result of stratospheric ozone depletion will influence the growth of Q. robur primarily through effects on leaf morphology.
Responses of stomatal conductance to light, humidity and temperature in winter wheat and barley grown at three concentrations of carbon dioxide in the field
Authors: Bunce James A. 
Published: March 2003

SummaryResponses of leaf stomatal conductance to light, humidity and temperature were characterized for winter wheat and barely grown at ambient (about 350 μmol mol−1 in the daytime), ambient + 175 and ambient + 350 μmol mol−1 concentrations of carbon dioxide in open‐topped chambers in field plots over a three year period. Stomatal responses to environment were determined by direct manipulation of single environmental factors, and those results were compared with responses derived from natural day to day variation in mid‐day stomatal conductance. The purpose of these experiments was to determine the magnitude of reduction in stomatal conductance at elevated [CO2], and to assess whether the relative response of conductance to elevated [CO2] was constant across light, humidity and temperature conditions. The results indicated that light, humidity and temperature all significantly affected the relative decrease in stomatal conductance at elevated [CO2]. The relative decrease in conductance with elevated [CO2] was greater at low light, low water vapour pressure difference, and high temperature in both species. For measurements made at saturating light near mid‐day, the ratio of mid‐day stomatal conductances at doubled [CO2] to that at ambient [CO2] ranged from 0.42 to 0.86, with a mean of 0.66 in barley, and from 0.33 to 0.80, with a mean of 0.56 in wheat. Day‐to‐day variation in the relative effect of elevated [CO2] on conductance was correlated with the relative stimulation of [CO2] assimilation rate and with temperature. Some limitations of multiple linear regression, multiplicative, and ‘Ball–Berry' models as summaries of the data are discussed. In barley, a better fit to the models occurred in individual years than for the combined data, and in wheat a better fit to the models occurred when data from near the end of the season were removed.
Net soil carbon input under ambient and elevated CO2 concentrations: isotopic evidence after 4 years
Authors: Van Kessel Chris , Horwath William R. , Hartwig Ueli , Harris David , LÜscher Andreas 
Published: March 2003

SummaryElevation of atmospheric CO2 concentration is predicted to increase net primary production, which could lead to additional C sequestration in terrestrial ecosystems. Soil C input was determined under ambient and Free Atmospheric Carbon dioxide Enrichment (FACE) conditions for Lolium perenne L. and Trifolium repens L. grown for four years in a sandy‐loam soil. The 13C content of the soil organic matter C had been increased by 5‰ compared to the native soil by prior cropping to corn (Zea mays) for > 20 years. Both species received low or high amounts of N fertilizer in separate plots. The total accumulated above‐ground biomass produced by L. perenne during the 4‐year period was strongly dependent on the amount of N fertilizer applied but did not respond to increased CO2. In contrast, the total accumulated above‐ground biomass of T. repens doubled under elevated CO2 but remained independent of N fertilizer rate. The C:N ratio of above‐ground biomass for both species increased under elevated CO2 whereas only the C:N ratio of L. perenne roots increased under elevated CO2. Root biomass of L. perenne doubled under elevated CO2 and again under high N fertilization. Total soil C was unaffected by CO2 treatment but dependent on species. After 4 years and for both crops, the fraction of new C (F‐value) under ambient conditions was higher (P= 0.076) than under FACE conditions: 0.43 vs. 0.38. Soil under L. perenne showed an increase in total soil organic matter whereas N fertilization or elevated CO2 had no effect on total soil organic matter content for both systems. The net amount of C sequestered in 4 years was unaffected by the CO2 concentration (overall average of 8.5 g C kg−1 soil). There was a significant species effect and more new C was sequestered under highly fertilized L. perenne. The amount of new C sequestered in the soil was primarily dependent on plant species and the response of root biomass to CO2 and N fertilization. Therefore, in this FACE study net soil C sequestration was largely depended on how the species responded to N rather than to elevated CO2.
Elevated atmospheric CO2 alters microbial population structure in a pasture ecosystem
Authors: Montealegre Constanza M. , Van Kessel Chris , Blumenthal Jürg M. , Hur Hor‐Gil , Hartwig Ueli A. , Sadowsky Michael J. 
Published: March 2003

SummaryAn increase in concentration of atmospheric CO2 is one major factor influencing global climate change. Among the consequences of such an increase is the stimulation of plant growth and productivity. Below‐ground microbial processes are also likely to be affected indirectly by rising atmospheric CO2 levels, through increased root growth and rhizodeposition rates. Because changes in microbial community composition might have an impact on symbiotic interactions with plants, the response of root nodule symbionts to elevated atmospheric CO2 was investigated. In this study we determined the genetic structure of 120 Rhizobium leguminosarum bv. trifolii isolates from white clover plants exposed to ambient (350 μmol mol−1) or elevated (600 μmol mol−1) atmospheric CO2 concentrations in the Swiss FACE (Free‐Air‐Carbon‐Dioxide‐Enrichment) facility. Polymerase Chain Reaction (PCR) fingerprinting of genomic DNA showed that the isolates from plants grown under elevated CO2 were genetically different from those isolates obtained from plants grown under ambient conditions. Moreover, there was a 17% increase in nodule occupancy under conditions of elevated atmospheric CO2 when strains of R. leguminosarum bv. trifolii isolated from plots exposed to CO2 enrichment were evaluated for their ability to compete for nodulation with those strains isolated from ambient conditions. These results indicate that a shift in the community composition of R. leguminosarum bv. trifolii occurred as a result of an increased atmospheric CO2 concentration, and that elevated atmospheric CO2 affects the competitive ability of root nodule symbionts, most likely leading to a selection of these particular strains to nodulate white clover.