bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plant growth chambers for the simultaneous control of soil and air temperatures, and of atmospheric carbon dioxide concentration
Authors: GORDON DENNIS C. , VAN VUUREN MARGRET M.I. , MARSHALL BRUCE , ROBINSON DAVID 
Published: April 2006

AbstractMany facilities for growing plants at elevated atmospheric concentrations of CO2 ([CO2]) neglect the control of temperature, especially of the soil. Soil and root temperatures in conventional, free‐standing pots often exceed those which would occur in the field at a given air temperature. A plant growth facility is described in which atmospheric CO2 can be maintained at different concentrations while soil and air temperatures mimic spatial and temporal patterns seen in the field. It consists of glasshouse‐located chambers in which [CO2] is monitored by an infra‐red gas analyser and maintained by injection of CO2 from a cylinder. Air is cooled by a heat exchange unit. Plants grow in soil in 1.2 m long containers that are surrounded by cooling coils and thermal insulation. Both [CO2] and temperature are controlled by customized software. Air temperature is programmed to follow a sine function of diurnal time. Soil temperature at a depth of 0.55 m is programmed to be constant. Temperature at 0.1 m depth varies as a damped, lagged function of air temperature; that at 1.0 m as a similar function of the 0.55 m temperature. [CO2] is maintained within 20 μmol mol−1 of target concentrations during daylight. A feature of the system is that plant material is labelled with a 13C enrichment different from that of carbon in soil organic matter. The operation of the system is illustrated with data collected in an experiment with spring wheat (Triticum aestivum L., cv Tonic) grown at ambient [CO2] and at [CO2] 350 μmol mol−1 greater than ambient.
The importance of climate and soils for estimates of net primary production: a sensitivity analysis with the terrestrial ecosystem model
Authors: PAN YUDE , MCGUIRE A. DAVID , KICKLIGHTER DAVID W. , MELILLO JERRY M. 
Published: April 2006

AbstractWe used the Terrestrial Ecosystem Model (TEM) to investigate how alternative input data sets of climate (temperature/precipitation), solar radiation, and soil texture affect estimates of net primary productivity (NPP) for the conterminous United States. At the continental resolution, the climates of Cramer and Leemans (C&L) and of the Vegetation/ Ecosystem Modelling and Analysis Project (VEMAP) represent cooler and drier conditions for the United States in comparison to the Legates and Willmott (L&W) climate, and cause 5.2% and 2.3% lower estimates of NPP. Solar radiation derived from C&L and given in VEMAP is 32% and 60% higher than the solar radiation data derived from Hahn cloudiness. These differences cause ∼ 8% and 10% lower NPP because of radiation‐induced water stress. In comparison to the FAO/CSRC soil texture, which represents most biomes with loam soils, the soil textures are finer (more silt and clay) in the Zobler and VEMAP data sets. The use of VEMAP soil textures instead of FAO/CSRC soil textures causes ∼ 3% higher NPP because enhanced volumetric soil moisture causes higher rates of nitrogen cycling, but use of the Zobler soil textures has little effect. In general, NPP estimates of TEM are more sensitive to alternative data sets at the biome and grid cell resolutions than at the continental resolution. At all spatial resolutions, the sensitivity of NPP estimates represents the impact of uncertainty among the alternative data sets we used in this study. The reduction of uncertainty in input data sets is required to improve the spatial resolution of NPP estimates by process‐based ecosystem models, and is especially important for improving assessments of the regional impacts of global change.
Effects of enhanced ultraviolet radiation and carbon dioxide concentration on the moss Hylocomium splendens
Authors: SONESSON MATS , CALLAGHAN TERRY V. , CARLSSON BENGT Å. 
Published: April 2006

AbstractIn a laboratory experiment interaction effects of UV‐B and CO2 on photosynthesis and growth of the moss Hylocomium splendens were studied. The plants were exposed to two CO2 levels (350 ppm and 600 ppm) and three UV‐B levels (no UV‐B, ambient UV‐B and that corresponding to 20% ozone depletion) for 5 months. The effects were recorded by measuring the photosynthetic response and growth of the plants.There was a statistically significant change in photosynthetic efficiency and maximum photosynthetic rates due to time and to enhanced CO2 concentration, whereas there was no effect due to UV‐B. There was a decreased growth due to both UV‐B and CO2 and an interaction effect on growth (in length). The UV‐B dose corresponding to the ambient level had a larger reducing effect on growth than the highest UV‐B dose. This was a counter‐intuitive result and the following tentative interpretation was made: differences in the measured UV‐A/UV‐B/PAR ratios between the treatments could explain the result provided there was a non‐linear response to UV over the range of irradiance levels used.
A new gas injection method to enhance spatial utilization within a Free‐Air CO2 Enrichment (FACE) system
Authors: WALKLATE P. J. , XU Z. G. , McLEOD A. R. 
Published: April 2006

AbstractVisual observations of smoke dispersion in a wind tunnel and a computational fluid dynamics (CFD) model were used to evaluate methods of improving the performance of Free‐Air COT Enrichment (FACE) Systems for field studies of the effects of elevated CO2 on vegetation. A special baffle, named an Enhanced Local Mixing (ELM) system, was observed to increase the turbulence and consequent dilution of fumigant gas in the atmosphere. Modelling results suggest that the ELM design reduces the spatial variation of fumigant gas concentration in small experimental plots. The potential reduction in CO2 use and costs warrants further evaluation under Held conditions.
Marine pollution and coral reefs
Authors: DUBINSKY ZVY , STAMBLER NOGA 
Published: April 2006

Coral reefs are exposed to many anthropogenic stresses increasing in impact and range, both on local and regional scales. The main ones discussed here are nutrient enrichment, sewage disposal, sedimentation, oil‐related pollution, metals and thermal pollution. The stress comprising the main topic of this article, eutrophication, is examined from the point of view of its physiological and ecological mechanisms of action, on a number of levels. Nutrient enrichment can introduce an imbalance in the exchange of nutrients between the zooxanthellae and the host coral, it reduces light penetration to the reef due to nutrient‐ stimulated phytoplankton growth, and, most harmful of all, may bring about proliferation of seaweeds. The latter rapidly outgrow, smother and eventually replace, the slow‐growing coral reef, adapted to cope with the low nutrient concentrations typical in tropical seas.Eutrophication seldom takes place by itself. Sewage disposal invariably results in nutrient enrichment, but it also enriches the water with organic matter which stimulates proliferation of oxygen‐consuming microbes. These may kill corals and other reef organisms, either directly by anoxia, or by related hydrogen sulfide production. Increased sediment deposition is in many cases associated with other human activities leading to eutrophication, such as deforestation and topsoil erosion.Realistically achievable goals to ensure conservation, and in some instances, rehabilitation of coral reefs are listed.
Global change and coral reefs: impacts on reefs, economies and human cultures
Authors: WILKINSON CLIVE R. 
Published: April 2006

AbstractCoral reefs have reconstituted themselves after previous large sea‐level variations, and climate changes. For the past 6000 years of unusually stable sea‐level, reefs have grown without serious interruptions. During recent decades, however, new stresses threaten localized devastation of many reefs. A new period of global climate change is occurring, stimulated by anthropogenic increases in greenhouse gases. Coral reefs will cope well with predicted sea‐level rises of 4.5 cm per decade, but reef islands will not. Higher sea levels will provide corals with greater room for growth across reef flats, but there are no foreseeable mechanisms for reef island growth to keep pace with sea‐level rise, therefore many low islands may ultimately become uninhabitable.Climate change will introduce localized variations in weather patterns, but changes to individual reefs cannot be predicted. Reefs on average should cope well with regional climate change, as they have coped with similar previous fluctuations. Air temperature increases of 0.2–0.3 °C/decade will induce slower increases in sea‐surface temperatures, which may cause localized, or regional increases in coral bleaching. Changes in rainfall will impact on reefs near land masses. Likewise, increased storms and variations in El Nino Southern Oscillation (ENSO) may stress some reefs, but not others.The greatest impact of climate change will be a synergistic enhancement of direct anthropogenic stresses (excessive sediment and pollution from the land; over‐fishing, especially via destructive methods; mining of coral rock and sand; and engineering modifications), which currently cause most damage to coral reefs. Many of the world's reefs have been degraded and more will be damaged as anthropogenic impacts increase under the ‘demophoric’ increases in population (demos) and economic (phoric) activity. This biotic and habitat loss will result in severe economic and social losses. Reefs, however, have considerable recovery powers and losses can be minimized by effective management of direct human impacts and reducing indirect threats of global climate change.
Reef coral diversity and global change
Authors: CHADWICK‐FURMAN NANETTE E. 
Published: April 2006

AbstractRegional anthropogenic processes such as pollution, dredging, and overfishing on coral reefs currently threaten the biodiversity of stony corals and other reef‐associated organisms. Global climate change may interact with anthropogenic processes to create additional impacts on coral diversity in the near future. In order to predict these changes, it is necessary to understand the magnitude and causes of variation in scleractinian coral diversity throughout their 240 million year history. The fossil record documents long periods of speciation in corals, interrupted repeatedly by events of mass extinction. Some of these events relate clearly to changes in global climate. Diversity in reef corals has increased since their last period of extinction at the end of the Cretaceous (65 My bp), and is still rising. During the last 8 million years, the fragmentation of the once pantropical Tethys Sea separated corals into two major biogeographical provinces. Periods of glaciation also have caused major changes in sea level and temperature. Accumulated evidence supports the theory that relative habitat area and changing patterns of oceanic circulation are mainly responsible for the two observed centres of recent coral diversity at the western tropical margins of the Atlantic and Pacific oceans. At predicted rates of climate change in the near future, coral reefs are likely to survive as an ecosystem. Increases in sea level may actually benefit corals and lead to regional increases in diversity if new habitat area on back reefs is opened to increased water circulation and thus coral dispersal. Rising temperature may cause higher rates of coral mortality and even local extinction in isolated, small populations such as those on oceanic islands. The effects of increases in ultraviolet radiation (UV) are largely unknown, but likely to be negative. UV may damage planktonic coral propagules in oceanic surface waters and thus decrease rates of gene flow between coral populations. This may result in increased local extinctions, again with the strongest impact on widely separated reefs with small coral populations. The largest threats to coral diversity are regional anthropogenic impacts, which may interact with global climate change to exacerbate rates of local species extinctions. Centres of high reef coral diversity coincide with human population centres in south‐east Asia and the Caribbean, and thus the greatest potential for species loss lies in these geographical areas.
Coral skeletons: storage and recovery of environmental information
Authors: BARNES D.J. , LOUGH J.M. 
Published: April 2006

AbstractUnderstanding the nature and causes of past global change is a key to understanding what may happen in the future. The discovery, nearly 25 years ago, of annual density bands in skeletons of long‐lived, massive corals promised high‐resolution proxy climate records for tropical oceans. The tropics are regions of major importance to the global climate system and they are poorly represented by high‐resolution proxy climate records such as tree rings, ice cores and historical documents.In this review we examine the principles and procedures underlying routine recovery and interpretation of information from proxy environmental recorders. We summarize an extensive literature which indicates that coral skeletons are excellent archives for considerable and diverse environmental information. We show that this potential has not been fully realized, largely because corals seemed to yield inconsistent, sometimes conflicting, information. We discuss ways in which much of this confusion is resolved by new understanding of coral skeletal growth mechanisms. We also examine several records which indicate that corals can meet requirements for reconstruction of useful, reliable environmental information.
Strategies for measuring and modelling carbon dioxide and water vapour fluxes over terrestrial ecosystems
Authors: BALDOCCHI DENNIS , VALENTINI RICCARDO , RUNNING STEVE , OECHEL WALT , DAHLMAN ROGER 
Published: April 2006

AbstractContinuous and direct measurements of ecosystem carbon dioxide and water vapour fluxes can improve our ability to close regional and global carbon and hydrological budgets. On this behalf, an international and multidisciplinary group of scientists (micrometeorologists, ecophysiologists and biogeochemists) assembled at La Thuile, Italy to convene a workshop on ‘Strategies for Monitoring and Modelling CO2 and Water Vapour Fluxes over Terrestrial Ecosystems’. Over the course of the week talks and discussions focused on: (i) the results from recent field studies on the annual cycle of carbon dioxide and water vapour fluxes over terrestrial ecosystems; (ii) the problems and pitfalls associated with making long‐term flux measurements; (iii) alternative methods for assessing ecosystem carbon dioxide and water vapour fluxes; (iv) how direct and continuous carbon dioxide and water vapour flux measurements could be used by the ecological and biogeochemical modelling communities; and (v) if, how and where to proceed with establishing a network of long‐term flux measurement sites. This report discusses the purpose of the meeting and summarizes the conclusions drawn from the discussions by the attending scientists.There was a consensus that recent advances in instrumentation and software make possible long‐term measurements of carbon dioxide and water vapour fluxes over terrestrial ecosystems. At this writing, eight research teams have conducted long‐term carbon dioxide and water vapour flux experiments and more long‐term studies are anticipated. The participants advocated an experimental design that would make long‐term flux measurement valuable to a wider community of modelers, biogeochemists and ecologists. A network of carbon dioxide and water vapour flux measurement stations should include ancillary measurements of meteorological, ecological and biological variables. To assess spatial representativeness of the long term and tower‐based flux measurements, periodic aircraft‐based flux experiments and satellite‐based assessments of land cover were recommended. Occasional cuvette‐based measurements of leaf‐level carbon dioxide and water vapour fluxes were endorsed to provide information on the biological control of surface fluxes. They can also provide data to parameterize ecophysiological models. Flask sampling of stable carbon isotopes was advocated to extend the flux measurements to the global scale.
The use of eddy covariance to infer the net carbon dioxide uptake of Brazilian rain forest
Authors: GRACE JOHN , MALHI YADVINDER , LLOYD JON , McINTYRE JOHN , MIRANDA ANTONIO C. , MEIR PATRICK , MIRANDA HELOISA S. 
Published: April 2006

Abstract

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.
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.
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.
The model also suggests that the effect of temperature on the net carbon balance is strongly dependent on the partial pressure of CO2.
The propagation of errors in long‐term measurements of land‐atmosphere fluxes of carbon and water
Authors: MONCRIEFF J.B. , MALHI Y. , LEUNING R. 
Published: April 2006

AbstractFor surface fluxes of carbon dioxide, the net daily flux is the sum of daytime and nighttime fluxes of approximately the same magnitude and opposite direction. The net flux is therefore significantly smaller than the individual flux measurements and error assessment is critical in determining whether a surface is a net source or sink of carbon dioxide. For carbon dioxide flux measurements, it is an occasional misconception that the net flux is measured as the difference between the net upward and downward fluxes (i.e. a small difference between large terms). This is not the case. The net flux is the sum of individual (half‐hourly or hourly) flux measurements, each with an associated error term. The question of errors and uncertainties in long‐term flux measurements of carbon and water is addressed by first considering the potential for errors in flux measuring systems in general and thus errors which are relevant to a wide range of timescales of measurement. We also focus exclusively on flux measurements made by the micrometeorological method of eddy covariance. Errors can loosely be divided into random errors and systematic errors, although in reality any particular error may be a combination of both types. Systematic errors can be fully systematic errors (errors that apply on all of the daily cycle) or selectively systematic errors (errors that apply to only part of the daily cycle), which have very different effects. Random errors may also be full or selective, but these do not differ substantially in their properties. We describe an error analysis in which these three different types of error are applied to a long‐term dataset to discover how errors may propagate through long‐term data and which can be used to estimate the range of uncertainty in the reported sink strength of the particular ecosystem studied.
Transpiration of trees and forest stands: short and long‐term monitoring using sapflow methods
Authors: GRANIER A. , BIRON P. , BRÉDA N. , PONTAILLER J.‐Y. , SAUGIER B. 
Published: April 2006

AbstractWe show that sapflow is a useful tool for studies of water fluxes in forest ecosystems, because (i) it gives access to the spatial variability within a forest stand, (ii) it can be used even on steep slopes, and (iii) when combined with eddy correlation measurements over forests, it allows separation of individual tree transpiration from the total water loss of the stand. Moreover, sapflow techniques are quite easy to implement.Four sapflow techniques currently coexist, all based on heat diffusion in the xylem. We found a good agreement between three of these techniques. Most results presented here were obtained using the radial flow meter (Granier 1985).Tree sapflow is computed as sap flux density times sapwood area. To scale up from trees to a stand, measurements have to be made on a representative sample of trees. Thus, a number of trees in each circumference class is selected according to the fraction of sapwood they represent in the total sapwood area of the stand. The variability of sap flux density among trees is usually low (CV. 10–15%) in close stands of temperate coniferous or deciduous forests, but is much higher (35–50%) in a tropical rain forest. It also increases after thinning or during a dry spell.A set of 5–10 sapflow sensors usually provides an accurate estimate of stand transpiration. Transpiration measured on two dense spruce stands in the Vosges mountains (France) and one Scot's pine plantation in the Rhine valley (Germany) showed that maximum rate was related to stand LAI and to local climate. Preliminary results comparing the sapflow of a stand of Pinus banksiana to the transpiration of large branches, as part of the BOREAS programme in Saskachewan, Canada showed a similar trend.For modelling purposes, tree canopy conductance (gc) was calculated from Penman‐Monteith equation. In most experiments, calculated canopy conductance was dependent on global radiation (positive effect) and on vapour pressure deficit (negative effect) in the absence of other limiting factors. A comparison of the vapour pressure deficit response curves of gc for several tree species and sites showed only small differences among spruce, oak and pine forests when including understorey. Tropical rainforests exhibited a similar behaviour.
The use of CO2 flux measurements in models of the global terrestrial carbon budget
Authors: RUIMY ANNE , KERGOAT LAURENT , FIELD CHRISTOPHER B. , SAUGIER BERNARD 
Published: April 2006

AbstractCO2 flux measurements give access to two critical terms of the carbon budget of terrestrial ecosystems, the gross primary productivity (GPP) and the net ecosystem productivity (NEP). CO2 fluxes measured by micrometeorological methods have spatial and temporal characteristics that make them potentially useful in modelling the global terrestrial carbon budget. The first use is in parameterizing ecosystem physiological processes. We present an example, based on parameterizing the mean light response of GPP. This parameterization can be used in diagnostic, satellite‐based GPP models. A global application leads to realistic estimates of global GPP. The second use is in testing the seasonality of fluxes predicted by global models. Our example of this use tests two global GPP models. One is a diagnostic, satellite‐based model, and one is a prognostic, process‐based model. Despite the limitations of the models, both agree reasonably well with the measurements. The agreements and disagreements are useful in addressing the problems of available input datasets and representation of processes, in global models. Long‐term CO2 flux measurements give access to key variables of terrestrial vegetation models and therefore offer exciting perspectives.